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Transuranic Elements are those numbered 92 and over.

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Mendelevium was the ninth transuranic element to be synthesized - 9 T E

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Mendelevium was the ninth transuranic element to be synthesized - 9 T E

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Mendelevium is a synthetic element with the symbol Md ( formerly Mv) and atomic number 101. A metallic radioactive transuranic element in the actinide series, it is the first element by atomic number that currently cannot be produced in macroscopic quantities through neutron bombardment of lighter elements. It is the third-to-last actinide and the ninth transuranic element. It can only be produced in particle accelerators by bombarding lighter elements with charged particles. A total of sixteen mendelevium isotopes are known, the most stable being ²⁵⁸Md with a half-life of 51 days; nevertheless, the shorter-lived ²⁵⁶Md (half-life 1.17 hours) is most commonly used in chemistry because it can be produced on a larger scale.

Mendelevium was discovered by bombarding einsteinium with alpha particles in 1955, the same method still used to produce it today. It was named after Dmitri Mendeleev, father of the periodic table of the chemical elements. Using available microgram quantities of the isotope einsteinium-253, over a million mendelevium atoms may be produced each hour. The chemistry of mendelevium is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. All of the isotopes of mendelevium have relatively short half-lives, there are currently no uses for it outside basic scientific research, and only small amounts are produced.

Mendelevium was the ninth transuranic element to be synthesized. It was first synthesized by Albert Ghiorso, Glenn T. Seaborg, Gregory Robert Choppin, Bernard G. Harvey, and team leader Stanley G. Thompson in early 1955 at the University of California, Berkeley. The team produced ²⁵⁶Md ( half-life of 77 minutes) when they bombarded an ²⁵³ Es target consisting of only a billion (10 ⁹) einsteinium atoms with alpha particles ( helium nuclei) in the Berkeley Radiation Laboratory's 60-inch cyclotron, thus increasing the target's atomic number by two. ²⁵⁶Md thus became the first isotope of any element to be synthesized one atom at a time. In total, seventeen mendelevium atoms were produced. This discovery was part of a program, begun in 1952, that irradiated plutonium with neutrons to transmute it into heavier actinides. This method was necessary as the previous method used to synthesize transuranic elements, neutron capture, could not work because of a lack of known beta decaying isotopes of fermium that would produce isotopes of the next element, mendelevium, and also due to the very short half-life to spontaneous fission of ²⁵⁸ Fm that thus constituted a hard limit to the success of the neutron capture process.

To predict if the production of mendelevium would be possible, the team made use of a rough calculation. The number of atoms that would be produced would be approximately equal to the product of the number of atoms of target material, the target's cross section, the ion beam intensity, and the time of bombardment; this last factor was related to the half-life of the product when bombarding for a time on the order of its half-life. This gave one atom per experiment. Thus under optimum conditions, the preparation of only one atom of element 101 per experiment could be expected. This calculation demonstrated that it was feasible to go ahead with the experiment. The target material, einsteinium-253, could be produced readily from irradiating plutonium: one year of irradiation would give a billion atoms, and its three-week half-life meant that the element 101 experiments could be conducted in one week after the produced einsteinium was separated and purified to make the target. However, it was necessary to upgrade the cyclotron to obtain the needed intensity of 10 ¹⁴ alpha particles per second; Seaborg applied for the necessary funds.

While Seaborg applied for funding, Harvey worked on the einsteinium target, while Thomson and Choppin focused on methods for chemical isolation. Choppin suggested using α-hydroxyisobutyric acid to separate the mendelevium atoms from those of the lighter actinides. The actual synthesis was done by a recoil technique, introduced by Albert Ghiorso. In this technique, the einsteinium was placed on the opposite side of the target from the beam, so that the recoiling mendelevium atoms would get enough momentum to leave the target and be caught on a catcher foil made of gold. This recoil target was made by an electroplating technique, developed by Alfred Chetham-Strode. This technique gave a very high yield, which was absolutely necessary when working with such a rare and valuable product as the einsteinium target material. The recoil target consisted of 10 ⁹ atoms of ²⁵³Es which were deposited electrolytically on a thin gold foil. It was bombarded by 41 MeV alpha particles in the Berkeley cyclotron with a very high beam density of 6×10 ¹³ particles per second over an area of 0.05 cm ². The target was cooled by water or liquid helium, and the foil could be replaced.

Initial experiments were carried out in September 1954. No alpha decay was seen from mendelevium atoms; thus, Ghiorso suggested that the mendelevium had all decayed by electron capture to fermium and that the experiment should be repeated to search instead for spontaneous fission events. The repetition of the experiment happened in February 1955.

On the day of discovery, 19 February, alpha irradiation of the einsteinium target occurred in three three-hour sessions. The cyclotron was in the University of California campus, while the Radiation Laboratory was on the next hill. To deal with this situation, a complex procedure was used: Ghiorso took the catcher foils (there were three targets and three foils) from the cyclotron to Harvey, who would use aqua regia to dissolve it and pass it through an anion-exchange resin column to separate out the transuranium elements from the gold and other products. The resultant drops entered a test tube, which Choppin and Ghiorso took in a car to get to the Radiation Laboratory as soon as possible. There Thompson and Choppin used a cation-exchange resin column and the α-hydroxyisobutyric acid. The solution drops were collected on platinum disks and dried under heat lamps. The three disks were expected to contain respectively the fermium, no new elements, and the mendelevium. Finally, they were placed in their own counters, which were connected to recorders such that spontaneous fission events would be recorded as huge deflections in a graph showing the number and time of the decays. There thus was no direct detection, but by observation of spontaneous fission events arising from its electron-capture daughter ²⁵⁶ Fm. The first one was identified with a "hooray" followed by a "double hooray" and a "triple hooray". The fourth one eventually officially proved the chemical identification of the 101st element, mendelevium. In total, five decays were reported up till 4 a.m. Seaborg was notified and the team left to sleep. Additional analysis and further experimentation showed the produced mendelevium isotope to have mass 256 and to decay by electron capture to fermium-256 with a half-life of 1.5 h.

We thought it fitting that there be an element named for the Russian chemist Dmitri Mendeleev, who had developed the periodic table. In nearly all our experiments discovering transuranium elements, we'd depended on his method of predicting chemical properties based on the element's position in the table. But in the middle of the Cold War, naming an element for a Russian was a somewhat bold gesture that did not sit well with some American critics.

Being the first of the second hundred of the chemical elements, it was decided that the element would be named "mendelevium" after the Russian chemist Dmitri Mendeleev, father of the periodic table. Because this discovery came during the Cold War, Seaborg had to request permission of the government of the United States to propose that the element be named for a Russian, but it was granted. The name "mendelevium" was accepted by the International Union of Pure and Applied Chemistry (IUPAC) in 1955 with symbol "Mv", which was changed to "Md" in the next IUPAC General Assembly (Paris, 1957).

In the periodic table, mendelevium is located to the right of the actinide fermium, to the left of the actinide nobelium, and below the lanthanide thulium. Mendelevium metal has not yet been prepared in bulk quantities, and bulk preparation is currently impossible. Nevertheless, a number of predictions and some preliminary experimental results have been done regarding its properties.

The lanthanides and actinides, in the metallic state, can exist as either divalent (such as europium and ytterbium) or trivalent (most other lanthanides) metals. The former have fnd ¹s ² configurations, whereas the latter have fn+1s ² configurations. In 1975, Johansson and Rosengren examined the measured and predicted values for the cohesive energies ( enthalpies of crystallization) of the metallic lanthanides and actinides, both as divalent and trivalent metals. The conclusion was that the increased binding energy of the [Rn]5f ¹²6d ¹7s ² configuration over the [Rn]5f ¹³7s ² configuration for mendelevium was not enough to compensate for the energy needed to promote one 5f electron to 6d, as is true also for the very late actinides: thus einsteinium, fermium, mendelevium, and nobelium were expected to be divalent metals. The increasing predominance of the divalent state well before the actinide series concludes is attributed to the relativistic stabilization of the 5f electrons, which increases with increasing atomic number. Thermochromatographic studies with trace quantities of mendelevium by Zvara and Hübener from 1976 to 1982 confirmed this prediction. In 1990, Haire and Gibson estimated mendelevium metal to have an enthalpy of sublimation between 134 and 142 kJ/mol. Divalent mendelevium metal should have a metallic radius of around . Like the other divalent late actinides (except the once again trivalent lawrencium), metallic mendelevium should assume a face-centered cubic crystal structure. Mendelevium's melting point has been estimated at 827 °C, the same value as that predicted for the neighboring element nobelium. Its density is predicted to be around .

The chemistry of mendelevium is mostly known only in solution, in which it can take on the +3 or +2 oxidation states. The +1 state has also been reported, but has not yet been confirmed.

Before mendelevium's discovery, Seaborg and Katz predicted that it should be predominantly trivalent in aqueous solution and hence should behave similarly to other tripositive lanthanides and actinides. After the synthesis of mendelevium in 1955, these predictions were confirmed, first in the observation at its discovery that it eluted just after fermium in the trivalent actinide elution sequence from a cation-exchange column of resin, and later the 1967 observation that mendelevium could form insoluble hydroxides and fluorides that coprecipitated with trivalent lanthanide salts. Cation-exchange and solvent extraction studies led to the conclusion that mendelevium was a trivalent actinide with an ionic radius somewhat smaller than that of the previous actinide, fermium. Mendelevium can form coordination complexes with 1,2-cyclohexanedinitrilotetraacetic acid (DCTA).

In reducing conditions, mendelevium(III) can be easily reduced to mendelevium(II), which is stable in aqueous solution. The standard reduction potential of the E°(Md ³⁺→Md ²⁺) couple was variously estimated in 1967 as −0.10 V or −0.20 V: later 2013 experiments established the value as −0.16±0.05 V. In comparison, E°(Md ³⁺→Md ⁰) should be around −1.74 V, and E°(Md ²⁺→Md ⁰) should be around −2.5 V. Mendelevium(II)'s elution behavior has been compared with that of strontium(II) and europium(II).

In 1973, mendelevium(I) was reported to have been produced by Russian scientists, who obtained it by reducing higher oxidation states of mendelevium with samarium(II). It was found to be stable in neutral water- ethanol solution and be homologous to caesium(I). However, later experiments found no evidence for mendelevium(I) and found that mendelevium behaved like divalent elements when reduced, not like the monovalent alkali metals. Nevertheless, the Russian team conducted further studies on the thermodynamics of cocrystallizing mendelevium with alkali metal chlorides, and concluded that mendelevium(I) had formed and could form mixed crystals with divalent elements, thus cocrystallizing with them. The status of the +1 oxidation state is still tentative.

Although E°(Md ⁴⁺→Md ³⁺) was predicted in 1975 to be +5.4 V, suggesting that mendelevium(III) could be oxidized to mendelevium(IV), 1967 experiments with the strong oxidizing agent sodium bismuthate were unable to oxidize mendelevium(III) to mendelevium(IV).

A mendelevium atom has 101 electrons, of which at least three (and perhaps four) can act as valence electrons. They are expected to be arranged in the configuration [Rn]5f ¹³7s ² (ground state term symbol ²F 7/2), although experimental verification of this electron configuration had not yet been made as of 2006. In forming compounds, three valence electrons may be lost, leaving behind a [Rn]5f ¹² core: this conforms to the trend set by the other actinides with their [Rn] 5fn electron configurations in the tripositive state. The first ionization potential of mendelevium was measured to be at most (6.58 ± 0.07) eV in 1974, based on the assumption that the 7s electrons would ionize before the 5f ones; this value has since not yet been refined further due to mendelevium's scarcity and high radioactivity. The ionic radius of hexacoordinate Md ³⁺ had been preliminarily estimated in 1978 to be around 91.2 pm; 1988 calculations based on the logarithmic trend between distribution coefficients and ionic radius produced a value of 89.6 pm, as well as an enthalpy of hydration of −3654±12 kJ/mol. Md ²⁺ should have an ionic radius of 115 pm and hydration enthalpy −1413 kJ/mol; Md⁺ should have ionic radius 117 pm.

Sixteen isotopes of mendelevium are known, with mass numbers from 245 to 260; all are radioactive. Additionally, five nuclear isomers are known: 245mMd, 247mMd, 249mMd, 254mMd, and 258mMd. Of these, the longest-lived isotope is ²⁵⁸Md with a half-life of 51.5 days, and the longest-lived isomer is 258mMd with a half-life of 58.0 minutes. Nevertheless, the shorter-lived ²⁵⁶Md (half-life 1.17 hours) is more often used in chemical experimentation because it can be produced in larger quantities from alpha particle irradiation of einsteinium. After ²⁵⁸Md, the next most stable mendelevium isotopes are ²⁶⁰Md with a half-life of 31.8 days, ²⁵⁷Md with a half-life of 5.52 hours, ²⁵⁹Md with a half-life of 1.60 hours, and ²⁵⁶ Md with a half-life of 1.17 hours. All of the remaining mendelevium isotopes have half-lives that are less than an hour, and the majority of these have half-lives that are less than 5 minutes.

The half-lives of mendelevium isotopes mostly increase smoothly from ²⁴⁵Md onwards, reaching a maximum at ²⁵⁸Md. Experiments and predictions suggest that the half-lives will then decrease, apart from ²⁶⁰Md with a half-life of 31.8 days, as spontaneous fission becomes the dominant decay mode due to the mutual repulsion of the protons posing a limit to the island of relative stability of long-lived nuclei in the actinide series.

Mendelevium-256, the chemically most important isotope of mendelevium, decays through electron capture 90% of the time and alpha decay 10% of the time. It is most easily detected through the spontaneous fission of its electron capture daughter fermium-256, but in the presence of other nuclides that undergo spontaneous fission, alpha decays at the characteristic energies for mendelevium-256 (7.205 and 7.139 MeV) can provide more useful identification.

The lightest mendelevium isotopes ( ²⁴⁵Md to ²⁴⁷Md) are mostly produced through bombardment of bismuth targets with heavy argon ions, while slightly heavier ones ( ²⁴⁸Md to ²⁵³Md) are produced by bombarding plutonium and americium targets with lighter ions of carbon and nitrogen. The most important and most stable isotopes are in the range from ²⁵⁴Md to ²⁵⁸Md and are produced through bombardment of einsteinium isotopes with alpha particles: einsteinium-253, -254, and -255 can all be used. ²⁵⁹Md is produced as a daughter of ²⁵⁹ No, and ²⁶⁰Md can be produced in a transfer reaction between einsteinium-254 and oxygen-18. Typically, the most commonly used isotope ²⁵⁶Md is produced by bombarding either einsteinium-253 or -254 with alpha particles: einsteinium-254 is preferred when available because it has a longer half-life and therefore can be used as a target for longer. Using available microgram quantities of einsteinium, femtogram quantities of mendelevium-256 may be produced.

The recoil momentum of the produced mendelevium-256 atoms is used to bring them physically far away from the einsteinium target from which they are produced, bringing them onto a thin foil of metal (usually beryllium, aluminium, platinum, or gold) just behind the target in a vacuum. This eliminates the need for immediate chemical separation, which is both costly and prevents reusing of the expensive einsteinium target. The mendelevium atoms are then trapped in a gas atmosphere (frequently helium), and a gas jet from a small opening in the reaction chamber carries the mendelevium along. Using a long capillary tube, and including potassium chloride aerosols in the helium gas, the mendelevium atoms can be transported over tens of meters to be chemically analyzed and have their quantity determined. The mendelevium can then be separated from the foil material and other fission products by applying acid to the foil and then coprecipitating the mendelevium with lanthanum fluoride, then using a cation-exchange resin column with a 10% ethanol solution saturated with hydrochloric acid, acting as an eluant. However, if the foil is made of gold and thin enough, it is enough to simply dissolve the gold in aqua regia before separating the trivalent actinides from the gold using anion-exchange chromatography, the eluant being 6 M hydrochloric acid.

Mendelevium can finally be separated from the other trivalent actinides using selective elution from a cation-exchange resin column, the eluant being ammonia α-HIB. Using the gas-jet method often renders the first two steps unnecessary. The above procedure is the most commonly used one for the separation of transeinsteinium elements.

Another possible way to separate the trivalent actinides is via solvent extraction chromatography using bis-(2-ethylhexyl) phosphoric acid (abbreviated as HDEHP) as the stationary organic phase and nitric acid as the mobile aqueous phase. The actinide elution sequence is reversed from that of the cation-exchange resin column, so that the heavier actinides elute later. The mendelevium separated by this method has the advantage of being free of organic complexing agent compared to the resin column; the disadvantage is that mendelevium then elutes very late in the elution sequence, after fermium.

Another method to isolate mendelevium exploits the distinct elution properties of Md ²⁺ from those of Es ³⁺ and Fm ³⁺. The initial steps are the same as above, and employs HDEHP for extraction chromatography, but coprecipitates the mendelevium with terbium fluoride instead of lanthanum fluoride. Then, 50 mg of chromium is added to the mendelevium to reduce it to the +2 state in 0.1 M hydrochloric acid with zinc or mercury. The solvent extraction then proceeds, and while the trivalent and tetravalent lanthanides and actinides remain on the column, mendelevium(II) does not and stays in the hydrochloric acid. It is then reoxidized to the +3 state using hydrogen peroxide and then isolated by selective elution with 2 M hydrochloric acid (to remove impurities, including chromium) and finally 6 M hydrochloric acid (to remove the mendelevium). It is also possible to use a column of cationite and zinc amalgam, using 1 M hydrochloric acid as an eluant, reducing Md(III) to Md(II) where it behaves like the alkaline earth metals. Thermochromatographic chemical isolation could be achieved using the volatile mendelevium hexafluoroacetylacetonate: the analogous fermium compound is also known and is also volatile.

Although few people come in contact with mendelevium, the International Commission on Radiological Protection has set annual exposure limits for the most stable isotope. For mendelevium-258, the ingestion limit was set at 9×10 ⁵ becquerels (1 Bq is equivalent to one decay per second), and the inhalation limit at 6000 Bq.

1. ^ Fournier, Jean-Marc (1976). "Bonding and the electronic structure of the actinide metals". Journal of Physics and Chemistry of Solids. 37 (2): 235-244. Bibcode:1976JPCS...37..235F. doi:10.1016/0022-3697(76)90167-0.

2. Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3-128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001

3. ^ Ghiorso, A.; Harvey, B.; Choppin, G.; Thompson, S.; Seaborg, Glenn T. (1955). New Element Mendelevium, Atomic Number 101. Physical Review. 98. pp. 1518-1519. Bibcode:1955PhRv...98.1518G. doi:10.1103/PhysRev.98.1518. ISBN 9789810214401.

4. Choppin, Gregory R. (2003). "Mendelevium". Chemical and Engineering News. 81 (36).

5. ^ 101. Mendelevium - Elementymology & Elements Multidict. Peter van der Krogt.

6. ^ Chemistry, International Union of Pure and Applied (1955). Comptes rendus de la confèrence IUPAC.

7. ^ Chemistry, International Union of Pure and Applied (1957). Comptes rendus de la confèrence IUPAC.

8. ^ Haire, Richard G. (2006). "Einsteinium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 1577-1620. doi:10.1007/1-4020-3598-5_12. ISBN 978-1-4020-3555-5.

9. Silva, pp. 1634-5

10. ^ Johansson, Börje; Rosengren, Anders (1975). "Generalized phase diagram for the rare-earth elements: Calculations and correlations of bulk properties". Physical Review B. 11 (8): 2836-2857. Bibcode:1975PhRvB..11.2836J. doi:10.1103/PhysRevB.11.2836.

11. ^ Hulet, E. K. (1980). "Chapter 12. Chemistry of the Heaviest Actinides: Fermium, Mendelevium, Nobelium, and Lawrencium". In Edelstein, Norman M. (ed.). Lanthanide and Actinide Chemistry and Spectroscopy. ACS Symposium Series. 131. pp. 239-263. doi:10.1021/bk-1980-0131.ch012. ISBN 9780841205680.

12. ^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. pp. 4.121-4.123. ISBN 978-1439855119.

13. ^ Toyoshima, Atsushi; Li, Zijie; Asai, Masato; Sato, Nozomi; Sato, Tetsuya K.; Kikuchi, Takahiro; Kaneya, Yusuke; Kitatsuji, Yoshihiro; Tsukada, Kazuaki; Nagame, Yuichiro; Schädel, Matthias; Ooe, Kazuhiro; Kasamatsu, Yoshitaka; Shinohara, Atsushi; Haba, Hiromitsu; Even, Julia (11 October 2013). "Measurement of the Md³⁺/Md²⁺ Reduction Potential Studied with Flow Electrolytic Chromatography". Inorganic Chemistry. 52 (21): 12311-3. doi:10.1021/ic401571h. PMID 24116851.

14. ^ Martin, W. C.; Hagan, Lucy; Reader, Joseph; Sugan, Jack (1974). "Ground Levels and Ionization Potentials for Lanthanide and Actinide Atoms and Ions" (PDF). J. Phys. Chem. Ref. Data. 3 (3): 771-9. Bibcode:1974JPCRD...3..771M. doi:10.1063/1.3253147. Archived from the original (PDF) on 2014-02-11.

15. David R. Lide (ed), ^ CRC Handbook of Chemistry and Physics, 84th Edition. CRC Press. Boca Raton, Florida, 2003; Section 10, Atomic, Molecular, and Optical Physics; Ionization Potentials of Atoms and Atomic Ions

16. Silva, pp. 1630-1

17. Nucleonica (2007-2014). "Universal Nuclide Chart". Nucleonica.

18. ^ Koch, Lothar (2000). "Transuranium Elements". Transuranium Elements, in Ullmann's Encyclopedia of Industrial Chemistry. Wiley. doi:10.1002/14356007.a27_167. ISBN 978-3527306732.

Hoffman, D.C., Ghiorso, A., Seaborg, G. T. The transuranium people: the inside story, (2000), 201-229

Morss, L. R., Edelstein, N. M., Fuger, J., The chemistry of the actinide and transactinide element, 3, (2006), 1630-1636

A Guide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1

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Mendelevium is a synthetic element with the symbol Md ( formerly Mv) and atomic number 101. A metallic radioactive transuranic element in the actinide series, it is the first element by atomic number that currently cannot be produced in macroscopic quantities through neutron bombardment of lighter elements.

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Mendeleev sculpture in Bratislava by Karol Lacko

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Mendeleev sculpture in Bratislava by Karol Lacko

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Monument to Russian chemist Dmitri Mendeleev designed by Slovak modernist sculptor Karol Lacko (1974) in front of the Faculty of Chemical and Food Technology (Fakulta chemické a potravinářské technologie) of the Slovak University of Technology (Slovenská technická univerzita) in Bratislava, Slovakia Stock Photo - Alamy

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Download this stock image: Monument to Russian chemist Dmitri Mendeleev designed by Slovak modernist sculptor Karol Lacko (1974) in front of the Faculty of Chemical and Food Technology (Fakulta chemické a potravinářské technologie) of the Slovak University of Technology (Slovenská technická univerzita) in Bratislava, Slovakia.

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Lawrence Livermore National Laboratory (LLNL)

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Lawrence Livermore National Laboratory (LLNL)

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Lawrence Livermore National Laboratory ( LLNL) is a federally funded research and development center in Livermore, California, United States. Originally established in 1952, the laboratory now is sponsored by the United States Department of Energy and administered by Lawrence Livermore National Security, LLC.

The lab was originally established as the University of California Radiation Laboratory, Livermore Branch in 1952 in response to the detonation of the Soviet Union's first atomic bomb during the Cold War. It later became autonomous in 1971 and was designated a national laboratory in 1981.

A federally funded research and development center, Lawrence Livermore Lab is primarily funded by the U.S. Department of Energy and it is managed privately and operated by Lawrence Livermore National Security, LLC (a partnership of the University of California, Bechtel, BWX Technologies, AECOM, and Battelle Memorial Institute in affiliation with the Texas A&M University System). In 2012, the laboratory had the synthetic chemical element livermorium (element 116) named after it.

The Livermore facility was co-founded by Edward Teller and Ernest Lawrence, then director of the Radiation Laboratory at Berkeley.

Aerial view of Lawrence Livermore National Laboratory

LLNL is a research and development institution for science and technology applied to national security. Its principal responsibility is ensuring the safety, security and reliability of the nation's nuclear weapons through the application of advanced science, engineering, and technology. The laboratory also applies its special expertise and multidisciplinary capabilities towards preventing the proliferation and use of weapons of mass destruction, bolstering homeland security, and solving other nationally important problems, including energy and environmental needs, scientific research and outreach, and economic competitiveness.

The laboratory is located on a 1 sq. mi.(2.6 km ²) site at the eastern edge of Livermore. It also operates a 7,000 acres (28 km ²) remote experimental test site known as Site 300, situated about 15 miles (24 km) southeast of the main lab site. LLNL has an annual budget of about $2.7 billion and a staff of nearly 9,000 employees.

LLNL was established in 1952, as the University of California Radiation Laboratory, Livermore Branch, an offshoot of the existing University of California Radiation Laboratory at Berkeley. The lab at Livermore was intended to spur innovation and provide competition to the nuclear weapon design laboratory at Los Alamos in New Mexico, home of the Manhattan Project that developed the first atomic weapons. The Livermore facility was co-founded by Edward Teller and Ernest Lawrence, director of the Radiation Laboratory at Berkeley.

The new laboratory was sited at a former naval air station of World War II. It was already home to several University of California Radiation Laboratory projects that were too large for its location in the Berkeley Hills above the UC campus, including one of the first experiments in the magnetic approach to confined thermonuclear reactions (i.e. fusion). About half an hour southeast of Berkeley, the Livermore site provided much greater security for classified projects than an urban university campus.

Lawrence tapped his former graduate student Herbert York, age 32, to run Livermore. Under York, the Lab had four main programs: Project Sherwood (the magnetic-fusion program), Project Whitney (the weapons-design program), diagnostic weapon experiments (both for the Los Alamos and Livermore laboratories), and a basic physics program. York and the new lab embraced the Lawrence "big science" approach, tackling challenging projects with physicists, chemists, engineers, and computational scientists working together in multidisciplinary teams. Lawrence died in August 1958 and shortly after, the university's board of regents named both laboratories for him, as the Lawrence Radiation Laboratory.

Historically, the Berkeley and Livermore laboratories have had very close relationships on research projects, business operations, and staff. The Livermore Lab was established initially as a branch of the Berkeley laboratory. The Livermore lab was not officially severed administratively from the Berkeley lab until 1971. To this day, in official planning documents and records, Lawrence Berkeley National Laboratory is designated as Site 100, Lawrence Livermore National Lab as Site 200, and LLNL's remote test location as Site 300.

The laboratory was renamed Lawrence Livermore Laboratory ( LLL) in 1971. On October 1, 2007 LLNS assumed management of LLNL from the University of California, which had exclusively managed and operated the Laboratory since its inception 55 years before. The laboratory was honored in 2012 by having the synthetic chemical element livermorium named after it.

The LLNS takeover of the laboratory has been controversial. In May 2013, an Alameda County jury awarded over $2.7 million to five former laboratory employees who were among 430 employees LLNS laid off during 2008. The jury found that LLNS breached a contractual obligation to terminate the employees only for "reasonable cause." The five plaintiffs also have pending age discrimination claims against LLNS, which will be heard by a different jury in a separate trial. There are 125 co-plaintiffs awaiting trial on similar claims against LLNS. The May 2008 layoff was the first layoff at the laboratory in nearly 40 years.

On March 14, 2011, the City of Livermore officially expanded the city's boundaries to annex LLNL and move it within the city limits. The unanimous vote by the Livermore city council expanded Livermore's southeastern boundaries to cover 15 land parcels covering 1,057 acres (4.28 km ²) that comprise the LLNL site. The site was formerly an unincorporated area of Alameda County. The LLNL campus continues to be owned by the federal government.

From its inception, Livermore focused on new weapon design concepts; as a result, its first three nuclear tests were unsuccessful. The lab persevered and its subsequent designs proved increasingly successful. In 1957, the Livermore Lab was selected to develop the warhead for the Navy's Polaris missile. This warhead required numerous innovations to fit a nuclear warhead into the relatively small confines of the missile nosecone.[citation needed ]

During the Cold War, many Livermore-designed warheads entered service. These were used in missiles ranging in size from the Lance surface-to-surface tactical missile to the megaton-class Spartan antiballistic missile. Over the years, LLNL designed the following warheads: W27 (Regulus cruise missile; 1955; joint with Los Alamos), W38 (Atlas/Titan ICBM; 1959), B41 (B52 bomb; 1957), W45 (Little John/Terrier missiles; 1956), W47 (Polaris SLBM; 1957), W48 (155-mm howitzer; 1957), W55 (submarine rocket; 1959), W56 (Minuteman ICBM; 1960), W58 (Polaris SLBM; 1960), W62 (Minuteman ICBM; 1964), W68 (Poseidon SLBM; 1966), W70 (Lance missile; 1969), W71 (Spartan missile; 1968), W79 (8-in. artillery gun; 1975), W82 (155-mm howitzer; 1978), B83 (modern strategic bomb; 1979), and W87 (LGM-118 Peacekeeper/MX ICBM; 1982). The W87 and the B83 are the only LLNL designs still in the U.S. nuclear stockpile.

With the collapse of the Soviet Union in 1991 and the end of the Cold War, the United States began a moratorium on nuclear testing and development of new nuclear weapon designs. To sustain existing warheads for the indefinite future, a science-based Stockpile Stewardship Program (SSP) was defined that emphasized the development and application of greatly improved technical capabilities to assess the safety, security, and reliability of existing nuclear warheads without the use of nuclear testing. Confidence in the performance of weapons, without nuclear testing, is maintained through an ongoing process of stockpile surveillance, assessment and certification, and refurbishment or weapon replacement.

With no new designs of nuclear weapons, the warheads in the U.S. stockpile must continue to function far past their original expected lifetimes. As components and materials age, problems can arise. Stockpile Life Extension Programs can extend system lifetimes, but they also can introduce performance uncertainties and require maintenance of outdated technologies and materials. Because there is concern that it will become increasingly difficult to maintain high confidence in the current warheads for the long term, the Department of Energy/National Nuclear Security Administration initiated the Reliable Replacement Warhead (RRW) Program. RRW designs could reduce uncertainties, ease maintenance demands, and enhance safety and security. In March 2007, the LLNL design was chosen for the Reliable Replacement Warhead. Since that time, Congress has not allocated funding for any further development of the RRW.

LLNL conducts research into the properties and behavior of plutonium to learn how plutonium performs as it ages and how it behaves under high pressure (e.g., with the impact of high explosives). Plutonium has seven temperature-dependent solid allotropes. Each possesses a different density and crystal structure. Alloys of plutonium are even more complex; multiple phases can be present in a sample at any given time. Experiments are being conducted at LLNL and elsewhere to measure the structural, electrical and chemical properties of plutonium and its alloys and to determine how these materials change over time. Such measurements will enable scientists to better model and predict plutonium's long-term behavior in the aging stockpile.

The Lab's plutonium research is conducted in a specially designed facility called the SuperBlock, with emphasis on safety and security. Work with highly enriched uranium is also conducted there. In March 2008, the National Nuclear Security Administration (NNSA) presented its preferred alternative for the transformation of the nation's nuclear weapons complex. Under this plan, LLNL would be a center of excellence for nuclear design and engineering, a center of excellence for high explosive research and development, and a science magnet in high-energy-density (i.e., laser) physics. In addition, most of its special nuclear material would be removed and consolidated at a more central, yet-to-be-named site.

On September 30, 2009, the NNSA announced that about two thirds of the special nuclear material (e.g., plutonium) at LLNL requiring the highest level of security protection had been removed from LLNL. The move was part of NNSA's efforts initiated in October 2006 to consolidate special nuclear material at five sites by 2012, with significantly reduced square footage at those sites by 2017. The federally mandated project intends to improve security and reduce security costs, and is part of NNSA's overall effort to transform the Cold War era "nuclear weapons" enterprise into a 21st-century "nuclear security" enterprise. The original date to remove all high-security nuclear material from LLNL, based on equipment capability and capacity, was 2014. NNSA and LLNL developed a timeline to remove this material as early as possible, accelerating the target completion date to 2012.

The Lab's work in global security aims to reduce and mitigate the dangers posed by the spread or use of weapons of mass destruction and by threats to energy and environmental security. Livermore has been working on global security and homeland security for decades, predating both the collapse of the Soviet Union in 1991 and the September 11, 2001, terrorist attacks. LLNL staff have been heavily involved in the cooperative nonproliferation programs with Russia to secure at-risk weapons materials and assist former weapons workers in developing peaceful applications and self-sustaining job opportunities for their expertise and technologies. In the mid-1990s, Lab scientists began efforts to devise improved biodetection capabilities, leading to miniaturized and autonomous instruments that can detect biothreat agents in a few minutes instead of the days to weeks previously required for DNA analysis.

Today, Livermore researchers address a spectrum of threats - radiological/nuclear, chemical, biological, explosives, and cyber. They combine physical and life sciences, engineering, computations, and analysis to develop technologies that solve real-world problems. Activities are grouped into five programs:

Nonproliferation. Preventing the spread of materials, technology, and expertise related to weapons of mass destruction (WMD) and detecting WMD proliferation activities worldwide.

Domestic security: Anticipating, innovating and delivering technological solutions to prevent and mitigate devastating high-leverage attacks on U.S. soil.

Defense: Developing and demonstrating new concepts and capabilities to help the Department of Defense prevent and deter harm to the nation, its citizens and its military forces.

Intelligence: Working at the intersection of science, technology, and analysis to provide insight into the threats to national security posed by foreign entities.

Energy and environmental security: Furnishing scientific understanding and technological expertise to devise energy and environmental solutions at global, regional and local scales.

LLNL supports capabilities in a broad range of scientific and technical disciplines, applying current capabilities to existing programs and developing new science and technologies to meet future national needs.

The LLNL chemistry, materials, and life science research focuses on chemical engineering, nuclear chemistry, materials science, and biology and bio-nanotechnology.

Physics thrust areas include condensed matter and high-pressure physics, optical science and high energy density physics, medical physics and biophysics, and nuclear, particle and accelerator physics.

In the area of energy and environmental science, Livermore's emphasis is on carbon and climate, energy, water and the environment, and the national nuclear waste repository.

The LLNL engineering activities include micro- and nanotechnology, lasers and optics, biotechnology, precision engineering, nondestructive characterization, modeling and simulation, systems and decision science, and sensors, imaging and communications.

The LLNL is very strong in computer science, with thrust areas in computing applications and research, integrated computing and communications systems, and cyber security.

Lawrence Livermore National Laboratory has worked out several energy technologies in the field of coal gasification, shale oil extraction, geothermal energy, advanced battery research, solar energy, and fusion energy. Main oil shale processing technologies worked out by the Lawrence Livermore National Laboratory are LLNL HRS (hot-recycled-solid), LLNL RISE ( extraction technology) and LLNL radiofrequency technologies.

Over its 60-year history, Lawrence Livermore has made many scientific and technological achievements, including:

Critical contributions to the U.S. nuclear deterrence effort through the design of nuclear weapons to meet military requirements and, since the mid-1980s, through the stockpile stewardship program, by which the safety and reliability of the enduring stockpile is ensured without underground nuclear testing.

Design, construction, and operation of a series of ever larger, more powerful, and more capable laser systems, culminating in the 192-beam National Ignition Facility (NIF), completed in 2009.

Advances in particle accelerator and fusion technology, including magnetic fusion, free-electron lasers, accelerator mass spectrometry, and inertial confinement fusion.

Breakthroughs in high-performance computing, including the development of novel concepts for massively parallel computing and the design and application of computers that can carry out hundreds of trillions of operations per second.

Development of technologies and systems for detecting nuclear, radiological, chemical, biological, and explosive threats to prevent and mitigate WMD proliferation and terrorism.

Development of extreme ultraviolet lithography (EUVL) for fabricating next-generation computer chips.

First-ever detection of massive compact halo objects (MACHOs), a suspected but previously undetected component of dark matter.

Advances in genomics, biotechnology, and biodetection, including major contributions to the complete sequencing of the human genome though the Joint Genome Institute and the development of rapid PCR (polymerase chain reaction) technology that lies at the heart of today's most advanced DNA detection instruments.

Development and operation of the National Atmospheric Release Advisory Center (NARAC), which provides real-time, multi-scale (global, regional, local, urban) modeling of hazardous materials released into the atmosphere.

Development of highest resolution global climate models and contributions to the International Panel on Climate Change which, together with former vice president Al Gore, was awarded the 2007 Nobel Peace Prize.

Invention of new healthcare technologies, including a microelectrode array for construction of an artificial retina, a miniature glucose sensor for the treatment of diabetes, and a compact proton therapy system for radiation therapy.

On July 17, 2009 LLNL announced that the Laboratory had received eight R&D 100 Awards - more than it had ever received in the annual competition. The previous LLNL record of seven awards was reached five times - in 1987, 1988, 1997, 1998 and 2006.

Also known as the "Oscars of invention", the awards are given each year for the development of cutting-edge scientific and engineering technologies with commercial potential. The awards raise LLNL's total number of awards since 1978 to 129.

On October 12, 2016, LLNL released the results of computerized modeling of Mars's moon Phobos, finding that it has a connection with keeping the Earth safe from asteroids.

In December, 2022 scientists at Lawrence Livermore National Laboratory announced, in a breakthrough for fusion power technology, that they have used the technique of inertial confinement fusion to achieve a net gain of energy. The National Ignition Facility (NIF) became the first fusion reactor to achieve breakeven on December 5, 2022, with an experiment producing 3.15 megajoules of energy from a 2.05 megajoule input of laser light for an energy gain of about 1.5.

National Ignition Facility

Biosecurity and Nanoscience Laboratory. Researchers apply advances in nanoscience to develop novel technologies for the detection, identification, and characterization of harmful biological pathogens (viruses, spores, and bacteria) and chemical toxins.

Center for Accelerator Mass Spectrometry: LLNL's Center for Accelerator Mass Spectrometry (CAMS) develops and applies a wide range of isotopic and ion-beam analytical tools used in basic research and technology development, addressing a spectrum of scientific needs important to the Laboratory, the university community, and the nation. CAMS is the world's most versatile and productive accelerator mass spectrometry facility, performing more than 25,000 AMS measurement operations per year.

High Explosives Applications Facility and Energetic Materials Center: At HEAF, teams of scientists, engineers, and technicians address nearly all aspects of high explosives: research, development and testing, material characterization, and performance and safety tests. HEAF activities support the Laboratory's Energetic Materials Center, a national resource for research and development of explosives, pyrotechnics, and propellants.

National Atmospheric Release Advisory Center: NARAC is a national support and resource center for planning, real-time assessment, emergency response, and detailed studies of incidents involving a wide variety of hazards, including nuclear, radiological, chemical, biological, and natural atmospheric emissions.

National Ignition Facility: This 192-beam, stadium-size laser system is used to compress fusion targets to conditions required for thermonuclear burn. Experiments at NIF study physical processes at conditions that exist only in the interior of stars and in exploding nuclear weapons (see National Ignition Facility and photon science).

Superblock: This unique high-security facility houses modern equipment for research and engineering testing of nuclear materials and is the place where plutonium expertise is developed, nurtured, and applied. Research on highly enriched uranium also is performed here.

Livermore Computing Complex: LLNL's Livermore Computing Complex houses some of the world's most powerful computers, including the 20 petaflop Sequoia, the 5-petaflop Vulcan system; Jade and Quartz systems at 3 petaflops each; the 970-teraflop Zin system; 431-teraflop Cab system; and additional large multi-core, multi-socket Linux clusters with various processor types. The newest machine, Sierra, occupied the No. 3 position on the TOP500 list in June 2018.[44] The complex has nearly 10,000 square feet of machine floor space, supporting both classified and unclassified national security programs.

Titan Laser: Titan is a combined nanosecond-long pulse and ultrashort-pulse (subpicosecond) laser, with hundreds of joules of energy in each beam. This petawatt-class laser is used for a range of high-energy density physics experiments, including the science of fast ignition for inertial confinement fusion energy.

Throughout its history, LLNL has been a leader in computers and scientific computing. Even before the Livermore Lab opened its doors, E.O. Lawrence and Edward Teller recognized the importance of computing and the potential of computational simulation. Their purchase of one of the first UNIVAC computers set the precedent for LLNL's history of acquiring and exploiting the fastest and most capable supercomputers in the world. A succession of increasingly powerful and fast computers have been used at the Lab over the years. LLNL researchers use supercomputers to answer questions about subjects such as materials science simulations, global warming, and reactions to natural disasters.

LLNL has a long history of developing computing software and systems. Initially, there was no commercially available software, and computer manufacturers considered it the customer's responsibility to develop their own. Users of the early computers had to write not only the codes to solve their technical problems, but also the routines to run the machines themselves. Today, LLNL computer scientists focus on creating the highly complex physics models, visualization codes, and other unique applications tailored to specific research requirements. A great deal of software also has been written by LLNL personnel to optimize the operation and management of the computer systems, including operating systems such as TOSS, operating system extensions such as CHAOS (Linux Clustering), and resource management packages such as SLURM. LLNL also initiated and continues leading the development of ZFS on Linux, the official port of ZFS to the Linux operating system.

Livermore Valley Open Campus (LVOC)

In August 2009, a joint venture was announced between Sandia National Laboratories/California campus and LLNL to create an open, unclassified research and development space called the Livermore Valley Open Campus (LVOC). The motivation for the LVOC stems from current and future national security challenges that require increased coupling to the private sector to understand threats and deploy solutions in areas such as high performance computing, energy and environmental security, cyber security, economic security, and non-proliferation.

The LVOC is modeled after research and development campuses found at major industrial research parks and other U.S. Department of Energy laboratories with campus-like security, a set of business and operating rules devised to enhance and accelerate international scientific collaboration and partnerships with U.S. government agencies, industry and academia. Ultimately, the LVOC will consist of an approximately 110-acre parcel along the eastern edge of the Livermore Laboratory and Sandia sites, and will house additional conference space, collaboration facilities and a visitor's center to support educational and research activities.

Objectives of LVOC

Enhance the two laboratories' national security missions by substantially increasing engagement with the private sector and academic community.

Stay at the forefront of the science, technology and engineering fields.

Ensure a quality future workforce by expanding opportunities for open engagement of the broader scientific community.

LLNL's principal sponsor is the Department of Energy/ National Nuclear Security Administration (DOE/NNSA) Office of Defense Programs, which supports its stockpile stewardship and advanced scientific computing programs. Funding to support LLNL's global security and homeland security work comes from the DOE/NNSA Office of Defense Nuclear Nonproliferation, as well as the Department of Homeland Security. LLNL also receives funding from DOE's Office of Science, Office of Civilian Radioactive Waste Management, and Office of Nuclear Energy. In addition, LLNL conducts work-for-others research and development for various Defense Department sponsors, other federal agencies, including NASA, Nuclear Regulatory Commission (NRC), National Institutes of Health, and Environmental Protection Agency, a number of California State agencies, and private industry.[citation needed ]

For Fiscal Year 2009 LLNL spent $1.497 billion on research and laboratory operations activities:

Research/Science Budget:

National Ignition Facility - $301.1 million

Nuclear Weapon Deterrent (Safety/Security/Reliability) - $227.2 million

Advance Simulation and Computing - $221.9 million

Nonproliferation - $152.2 million

Department of Defense - $125.9 million

Basic and Applied Science - $86.6 million

Homeland Security - $83.9 million

Energy - $22.4 million

Site Management/Operations Budget:

Safeguards/Security - $126.5 million

Facility Operations - $118.2 million

Environmental Restoration - $27.3 million

The LLNL director is appointed by the board of governors of Lawrence Livermore National Security, LLC (LLNS) and reports to the board. The laboratory director also serves as the president of LLNS. Over the course of its history, the following scientists have served as LLNL director:

The LLNL director is supported by a senior executive team consisting of the deputy director, the deputy director for science and technology, principal associate directors, and other senior executives who manage areas/functions directly reporting to the laboratory director.

The director's office is organized into these functional areas/offices:

Chief Information Office

Contractor Assurance and Continuous Improvement

Environment, Safety and Health

Government and External Relations

Independent Audit and Oversight

Office of General Counsel

Prime Contract Management Office

Quality Assurance Office

Security Organization

LLNS, LLC Parent Oversight Office

The laboratory is organized into four principal directorates, each headed by a principal associate director:

Global Security

Weapons and Complex Integration

National Ignition Facility and Photon Science

Operations and Business

Business

Facilities & Infrastructure

Institutional Facilities Management

Integrated Safety Management System Project Office

Nuclear Operations

Planning and Financial Management

Staff Relations

Strategic Human Resources Management

Three other directorates are each headed by an associate director who reports to the LLNL director:

Computation

Engineering

Physical & Life Sciences

The LLNL director reports to the Lawrence Livermore National Security, LLC (LLNS) board of governors, a group of key scientific, academic, national security and business leaders from the LLNS partner companies that jointly own and control LLNS. The LLNS board of governors has a total of 16 positions, with six of these governors constituting an executive committee. All decisions of the board are made by the governors on the executive committee. The other governors are advisory to the executive committee and do not have voting rights.

The University of California is entitled to appoint three governors to the executive committee, including the chair. Bechtel is also entitled to appoint three governors to the executive committee, including the vice chair. One of the Bechtel governors must be a representative of Babcock & Wilcox (B&W) or the Washington Division of URS Corporation (URS), who is nominated jointly by B&W and URS each year, and who must be approved and appointed by Bechtel. The executive committee has a seventh governor who is appointed by Battelle; they are non-voting and advisory to the executive committee. The remaining board positions are known as independent governors (also referred to as outside governors), and are selected from among individuals, preferably of national stature, and can not be employees or officers of the partner companies.

The University of California-appointed chair has tie-breaking authority over most decisions of the executive committee. The board of governors is the ultimate governing body of LLNS and is charged with overseeing the affairs of LLNS in its operations and management of LLNL.

LLNS managers and employees who work at LLNL, up to and including the president and laboratory director, are generally referred to as laboratory employees. All laboratory employees report directly or indirectly to the LLNS president. While most of the work performed by LLNL is funded by the federal government, laboratory employees are paid by LLNS, which is responsible for all aspects of their employment, including providing health care benefits and retirement programs.

Within the board of governors, authority resides in the executive committee to exercise all rights, powers, and authorities of LLNS, excepting only certain decisions that are reserved to the parent companies. The LLNS executive committee is free to appoint officers or other managers of LLNS and LLNL, and may delegate its authorities as it deems appropriate to such officers, employees, or other representatives of LLNS/LLNL. The executive committee may also retain auditors, attorneys, or other professionals as necessary. For the most part the executive committee has appointed senior managers at LLNL as the primary officers of LLNS. As a practical matter most operational decisions are delegated to the president of LLNS, who is also the laboratory director. The positions of president laboratory director and deputy laboratory director are filled by joint action of the chair and vice chair of the executive committee, with the University of California nominating the president and laboratory director and Bechtel nominating the deputy laboratory director.

The current LLNS chairman is Norman J. Pattiz, founder and chairman of Westwood One, America's largest radio network, who also currently serves on the board of regents of the University of California. The vice chairman is J. Scott Ogilvie, president of Bechtel Systems & Infrastructure, Inc., who also serves on the board of directors of Bechtel Group, Inc. (BGI) and on the BGI Audit Committee.

The Livermore Action Group organized many mass protests, from 1981 to 1984, against nuclear weapons which were being produced by the Lawrence Livermore National Laboratory. Peace activists Ken Nightingale and Eldred Schneider were involved. On June 22, 1982, more than 1,300 anti-nuclear protesters were arrested in a nonviolent demonstration. More recently, there has been an annual protest against nuclear weapons research at Lawrence Livermore. In August 2003, 1,000 people protested at Livermore Labs against "new-generation nuclear warheads". In the 2007 protest, 64 people were arrested. More than 80 people were arrested in March 2008 while protesting at the gates.

On July 27, 2021, the Society of Professionals, Scientists, and Engineers - University of Professional & Technical Employees Local 11, CWA Local 9119, went on a three-day strike over unfair labor practices.

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Lawrence Livermore National Laboratory - Wikipedia

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Lawrence Livermore National Laboratory ( LLNL) is a federally funded research and development center in Livermore, California, United States. Originally established in 1952, the laboratory now is sponsored by the United States Department of Energy and administered by Lawrence Livermore National Security, LLC.

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Victor Ninov ( Bulgarian: Виктор Нинов, born June 27, 1959) is a Bulgarian physicist and former researcher who worked primarily in creating heavy elements. He is known for the co-discoveries of elements 110, 111, and 112 (darmstadtium, roentgenium and copernicium).

Ninov also claimed the creation of elements 116 and 118; however, an investigation concluded that he had falsified the evidence. The repercussions of the affair had an impact on the guidelines of conduct for several research institutions.

Victor Ninov was born in Bulgaria on June 27, 1959. He grew up in the capital city of Sofia. In the 1970s, when Ninov was a teenager, he and his family left for West Germany; they bounced around from house to house. Shortly after the move Victor's father went missing; he was found dead six months later in the Bulgarian foothills due to causes unknown.

Victor Ninov attended Technische Universität Darmstadt near Frankfurt, Germany. Here he distinguished himself as very capable physicist: he was particularly good at building scientific instruments and coding analysis programs for them.

This landed him a job at the nearby German research center GSI (Helmholtzzentrum für Schwerionenforschung) where he worked on his doctorate and postdoctoral work of creating new elements.

For his expertise he was given sole control of the computer analysis program. Here he became a rising star by co-discovering darmstadtium (element 110), roentgenium (element 111), and copernicium (element 112) by smashing ion beams into heavy elements using GSI's UNILAC (a type of particle accelerator) and analyzing the debris. Though an investigation later determined that these discoveries of element 110 and 112 included fabricated samples created by Ninov, additional evidence of the experiment was confirmed to be untampered with, rendering his co-discovery legitimate. These discoveries were made with the help of his addition of a gas separator to the particle accelerator to help filter out everything but the heavy elements they were looking for.

He worked at Stanford University for a time. He was hired at Lawrence Berkeley National Laboratory (LBNL) in 1996 as a world class expert for particle accelerator debris sensors, and analysis programs.

While working at Lawrence Berkeley National Laboratory (LBNL) Victor Ninov and his team pursued a hypothesis that element 118 could be formed at relatively low energies by smashing and isotopes together. Ninov initially doubted the hypothesis he was pursuing; he is quoted in saying "We didn't know how many orders of magnitude he was wrong" of the scientist who created the hypothesis.

Ninov, again, held sole control of the data analysis program called GOOSY, and he was the only one on the team that knew how to use it. In 1999 Ninov and his team reported sightings of element 118, almost exactly as predicted, and a decay chain that also produced element 116. However, other laboratories were unable to reproduce the results.

Eager to prove their discovery, the team double checked their instruments, and tried again. One more sighting was made by Ninov, but it was dismissed by a colleague, and a full formal investigation was spawned to get to the bottom of elements 118 and 116. The original element 118 data was independently analysed, and in the original binary data, there was no indication of the presence of element 118 or 116. The investigation dragged on for a year, until it was concluded that "Ninov... intentionally misled his colleagues-and everyone else-by fabricating data".

Ninov, who had been placed on leave, was fired. The rest of Ninov's team officially retracted their claims in 2002. There was also an investigation conducted into Ninov's unsupervised science at GSI; it was found that "two sightings were spuriously created" (one of element 110 and another of element 112). However, very perplexingly, these false flags were found amongst lots of real data that still supported that his co-discoveries were legitimate. It was the conclusion of the GSI investigation that the discovery of those elements was legitimate. At minimum it is certain that Victor Ninov made a "wrongful claim" about elements 116 and 118.

The heavy elements 116 and 118 were eventually discovered and verified in the Joint Institute for Nuclear Research in Dubna, Russia, and were observed contrary to LBNL's observations. These elements were named livermorium and oganesson respectively. Ninov maintains that he was innocent to this day.

Impact on the scientific community

The reports of the investigation came as quite a shock to other scientists as Ninov had been previously regarded as a very respected physicist. In the aftermath of the investigation it was troubling to many that so many co-authors on the papers about LBNL were none the wiser to learn they had contributed to a false statement. The Ninov affair resulted in stricter guidelines being set for coauthors; these rules "clarify co-authors' roles and duties" and they are "requiring all coauthors to vouch for their contribution to published work".

The American Physical Society has also called for increased ethical training and oversight at research institutions, and has sponsored several speakers in an effort to make the scientific community more comfortable and resilient to scientific fraud. Reports on the Ninov affair were released around the same time as the final report on the Schön affair, another major incident of data falsification in physics, and this amplified its impact.

Ninov is retired from physics. He lives in California. His wife, Caroline Cox, a former history professor at University of the Pacific, died in 2014 of cancer. They were married for 29 years. Ninov helped finish her book, Boy Soldiers of the American Revolution, and it was published postmortem. He is an avid sailor, and pilots a four-seat plane.

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Victor Ninov ( Bulgarian: Виктор Нинов, born June 27, 1959) is a Bulgarian physicist and former researcher who worked primarily in creating heavy elements. He is known for the co-discoveries of elements 110, 111, and 112 (darmstadtium, roentgenium and copernicium). Ninov also claimed the creation of elements 116 and 118; however, an investigation concluded that he had falsified the evidence.

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Lawrence Berkeley National Laboratory ( LBNL), commonly referred to as Berkeley Lab, is a United States national laboratory that is owned by, and conducts scientific research on behalf of, the United States Department of Energy. Located in the hills of Berkeley, California, the lab overlooks the campus of the University of California, Berkeley, and is managed by the University of California system.

The laboratory was founded on August 26, 1931, by Ernest Lawrence, as the Radiation Laboratory of the University of California, Berkeley, associated with the Physics Department. It centered physics research around his new instrument, the cyclotron, a type of particle accelerator for which he was awarded the Nobel Prize in Physics in 1939. Throughout the 1930s, Lawrence pushed to create larger and larger machines for physics research, courting private philanthropists for funding. He was the first to develop a large team to build big projects to make discoveries in basic research. Eventually these machines grew too large to be held on the university grounds, and in 1940 the lab moved to its current site atop the hill above campus. Part of the team put together during this period includes two other young scientists who went on to direct large laboratories; J. Robert Oppenheimer directed Los Alamos Laboratory, and Robert Wilson directed Fermilab.

Leslie Groves visited Lawrence's Radiation Laboratory in late 1942 as he was organizing the Manhattan Project, meeting J. Robert Oppenheimer for the first time. Oppenheimer was tasked with organizing the nuclear bomb development effort and founded today's Los Alamos National Laboratory to help keep the work secret. At the RadLab, Lawrence and his colleagues developed the technique of electromagnetic enrichment of uranium using their experience with cyclotrons. The calutrons (named after the University) became the basic unit of the massive Y-12 facility in Oak Ridge, Tennessee. Lawrence's lab helped contribute to what have been judged to be the three most valuable technology developments of the war (the atomic bomb, proximity fuze, and radar). The cyclotron, whose construction was stalled during the war, was finished in November 1946. The Manhattan Project shut down two months later.

After the war, the Radiation Laboratory became one of the first laboratories to be incorporated into the Atomic Energy Commission (AEC) (now Department of Energy, DOE). The most highly classified work remained at Los Alamos, but the RadLab remained involved. Edward Teller suggested setting up a second lab similar to Los Alamos to compete with their designs. This led to the creation of an offshoot of the RadLab (now the Lawrence Livermore National Laboratory) in 1952. Some of the RadLab's work was transferred to the new lab, but some classified research continued at Berkeley Lab until the 1970s, when it became a laboratory dedicated only to unclassified scientific research.

Shortly after the death of Lawrence in August 1958, the UC Radiation Laboratory (both branches) was renamed Lawrence Radiation Laboratory. The Berkeley location became Lawrence Berkeley Laboratory in 1971, although many continued to call it the RadLab. Gradually, another shortened form came into common usage, LBL. Its formal name was amended to Ernest Orlando Lawrence Berkeley National Laboratory in 1995, when "National" was added to the names of all DOE labs. "Ernest Orlando" was later dropped to shorten the name. Today, the lab is commonly referred to as Berkeley Lab.

The Alvarez Physics Memos are a set of informal working papers of the large group of physicists, engineers, computer programmers, and technicians led by Luis W. Alvarez from the early 1950s until his death in 1988. Over 1700 memos are available on-line, hosted by the Laboratory.

In 2018, the lab remains owned by the U.S. Department of Energy, with management from the University of California. Companies such as Intel were funding the lab's research into computing chips.

From the 1950s through the present, Berkeley Lab has maintained its status as a major international center for physics research, and has also diversified its research program into almost every realm of scientific investigation. Its mission is to solve the most pressing and profound scientific problems facing humanity, conduct basic research for a secure energy future, understand living systems to improve the environment, health, and energy supply, understand matter and energy in the universe, build and safely operate leading scientific facilities for the nation, and train the next generation of scientists and engineers

The Laboratory's 20 scientific divisions are organized within six areas of research: Computing Sciences, Physical Sciences, Earth and Environmental Sciences, Biosciences, Energy Sciences, and Energy Technologies. Berkeley Lab has six main science thrusts: advancing integrated fundamental energy science, integrative biological and environmental system science, advanced computing for science impact, discovering the fundamental properties of matter and energy, accelerators for the future, and developing energy technology innovations for a sustainable future. It was Lawrence's belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab tradition that continues today.

Berkeley Lab operates five major National User Facilities for the DOE Office of Science:

1. The Advanced Light Source (ALS) is a synchrotron light source with 41 beam lines providing ultraviolet, soft x-ray, and hard x-ray light to scientific experiments. The ALS is one of the world's brightest sources of soft x-rays, which are used to characterize the electronic structure of matter and to reveal microscopic structures with elemental and chemical specificity. About 2,500 scientist-users carry out research at ALS every year. Berkeley Lab is proposing an upgrade of ALS which would increase the coherent flux of soft x-rays by two-three orders of magnitude.

2. The Joint Genome Institute (JGI) supports genomic research in support of the DOE missions in alternative energy, global carbon cycling, and environmental management. The JGI's partner laboratories are Berkeley Lab, Lawrence Livermore National Lab (LLNL), Oak Ridge National Laboratory (ORNL), Pacific Northwest National Laboratory (PNNL), and the HudsonAlpha Institute for Biotechnology. The JGI's central role is the development of a diversity of large-scale experimental and computational capabilities to link sequence to biological insights relevant to energy and environmental research. Approximately 1,200 scientist-users take advantage of JGI's capabilities for their research every year. The foundation of Intel cofounder and Berkeley alumnus Gordon Moore has, since the institute's founding, provided over $9.4 million in funding.

3. The Molecular Foundry is a multidisciplinary nanoscience research facility. Its seven research facilities focus on Imaging and Manipulation of Nanostructures, Nanofabrication, Theory of Nanostructured Materials, Inorganic Nanostructures, Biological Nanostructures, Organic and Macromolecular Synthesis, and Electron Microscopy. Approximately 700 scientist-users make use of these facilities in their research every year.

4. The National Energy Research Scientific Computing Center (NERSC) is the scientific computing facility that provides large-scale computing for the DOE's unclassified research programs. Its current systems provide over 3 billion computational hours annually. NERSC supports 6,000 scientific users from universities, national laboratories, and industry.

5. The Energy Sciences Network (ESnet) is a high-speed network infrastructure optimized for very large scientific data flows. ESNet provides connectivity for all major DOE sites and facilities, and the network transports roughly 35 petabytes of traffic each month.

Berkeley Lab is the lead partner in the Joint BioEnergy Institute (JBEI), located in Emeryville, California. Other partners are the Sandia National Laboratories, the University of California (UC) campuses of Berkeley and Davis, the Carnegie Institution for Science, and Lawrence Livermore National Laboratory (LLNL). JBEI's primary scientific mission is to advance the development of the next generation of biofuels - liquid fuels derived from the solar energy stored in plant biomass. JBEI is one of three new U.S. Department of Energy (DOE) Bioenergy Research Centers (BRCs).

Berkeley Lab has a major role in two DOE Energy Innovation Hubs. The mission of the Joint Center for Artificial Photosynthesis (JCAP) is to find a cost-effective method to produce fuels using only sunlight, water, and carbon dioxide. The lead institution for JCAP is the California Institute of Technology and Berkeley Lab is the second institutional center. The mission of the Joint Center for Energy Storage Research (JCESR) is to create next-generation energy storage technologies that will transform transportation and the electricity grid. Argonne National Laboratory leads JCESR and Berkeley Lab is a major partner.

The University of California operates Lawrence Berkeley National Laboratory under a contract with the Department of Energy. The site consists of 76 buildings (owned by the U.S. Department of Energy) located on 200 acres (0.81 km ²) owned by the university in the Berkeley Hills. Altogether, the Lab has some 4,000 UC employees, of whom about 800 are students or postdocs, and each year it hosts more than 3,000 participating guest scientists. There are approximately two dozen DOE employees stationed at the laboratory to provide federal oversight of Berkeley Lab's work for the DOE. The laboratory director, Michael Witherell, is appointed by the university regents and reports to the university president. Although Berkeley Lab is governed by UC independently of the Berkeley campus, the two entities are closely interconnected: more than 200 Berkeley Lab researchers hold joint appointments as UC Berkeley faculty.

The Lab's budget for the fiscal year 2019 was US$1.1 billion dollars.

Scientific achievements, inventions, and discoveries

Notable scientific accomplishments at the Lab since World War II include the observation of the antiproton, the discovery of several transuranic elements, and the discovery of the accelerating universe.

Since its inception, 15 researchers associated with Berkeley Lab ( Ernest Lawrence, Glenn T. Seaborg, Edwin M. McMillan, Owen Chamberlain, Emilio G. Segrè, Donald A. Glaser, Melvin Calvin, Luis W. Alvarez, Yuan T. Lee, Steven Chu, George F. Smoot, Saul Perlmutter, Jennifer Doudna, John Clauser and Carolyn Bertozzi) have been awarded either the Nobel Prize in Physics or the Nobel Prize in Chemistry. In addition, twenty-three Berkeley Lab employees, as contributors to the Intergovernmental Panel on Climate Change, shared the 2007 Nobel Peace Prize with former Vice President Al Gore.

Seventy Berkeley Lab scientists are members of the U.S. National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen Berkeley Lab scientists have won the National Medal of Science, the nation's highest award for lifetime achievement in fields of scientific research. Eighteen Berkeley Lab engineers have been elected to the National Academy of Engineering, and three Berkeley Lab scientists have been elected into the National Academy of Medicine. Nature Index rates the Lab fifth in the world among government research organizations; it is the only one of the top six that is a single laboratory, rather than a system of laboratories.

Elements discovered by Berkeley Lab physicists include astatine, neptunium, plutonium, americium, curium, berkelium*, californium*, einsteinium, fermium, mendelevium, nobelium, lawrencium*, dubnium, and seaborgium*. Those elements listed with asterisks (*) are named after the University Professors Lawrence and Seaborg. Seaborg was the principal scientist involved in their discovery. The element technetium was discovered after Ernest Lawrence gave Emilio Segrè a molybdenum strip from the Berkeley Lab cyclotron. The fabricated evidence used to claim the creation of oganesson and livermorium by Victor Ninov, a researcher employed at Berkeley Lab, led to the retraction of two articles.

Inventions and discoveries to come out of Berkeley Lab include: "smart" windows with embedded electrodes that enable window glass to respond to changes in sunlight, synthetic genes for antimalaria and anti-AIDS superdrugs based on breakthroughs in synthetic biology, electronic ballasts for more efficient lighting, Home Energy Saver, the web's first do-it-yourself home energy audit tool, a pocket-sized DNA sampler called the PhyloChip, and the Berkeley Darfur Stove, which uses one-quarter as much firewood as traditional cook stoves. One of Berkeley Lab's most notable breakthroughs is the discovery of dark energy. During the 1980s and 1990s Berkeley Lab physicists and astronomers formed the Supernova Cosmology Project (SCP), using Type Ia supernovae as "standard candles" to measure the expansion rate of the universe. Their successful methods inspired competition, with the result that early in 1998 both the SCP and the High-Z Supernova Search Team announced the surprising discovery that expansion is accelerating; the cause was soon named dark energy.

Arthur Rosenfeld, a senior scientist at Berkeley Lab, was a prominent advocate for energy efficiency from 1975 until his death in 2017. He led efforts at the Lab that produced several technologies that radically improved efficiency: compact fluorescent lamps, low-energy refrigerators, and windows that trap heat. He established the Center for Building Science at the Lab, which developed into the Building Technology and Urban Systems Division. He developed the first energy-efficiency standards for buildings and appliances in California, which helped the state to sustain constant electricity use per capita, a phenomenon called the Rosenfeld effect. The Energy Efficiency and Environmental Impacts Division continues to set the research foundation for the national energy efficiency standards and works with China, India, and other countries to help develop their standards.

Carl Haber and Vitaliy Fadeyev of Berkeley Lab developed the IRENE system for optical scanning of audio discs and cylinders.

In December 2018, researchers at Intel Corp. and Lawrence Berkeley National Laboratory published a paper in Nature, which outlined a chip "made with quantum materials called magnetoelectric multiferroics instead of the conventional silicon," to allow for increased processing and reduced energy consumption to support technology such as artificial intelligence.

Haimei Zheng, Chinese-American materials scientist and Senior Staff Scientist

Historic American Engineering Record (HAER) No. CA-186-A, "University of California Radiation Laboratory, Bevatron", 132 photos, 149 data pages, 14 photo caption pages

HAER No. CA-186-B, "University of California Radiation Laboratory, SuperHilac", 18 photos, 17 data pages, 2 photo caption pages

"University of California Office of Laboratory Management". University of California.

"The Rad Lab - Ernest Lawrence and the Cyclotron". American Institute of Physics.

Heilbron, J. L.; Seidel, Robert W.; Wheaton, Bruce R. "Lawrence and His Laboratory: A Historian's View of the Lawrence Years". Lawrence Berkeley National Laboratory.

"A Century of Physics at Berkeley: Seedtime for "Big Science", 1930-1950". University of California, Berkeley.

"SPIE Video: Paul Alivisatos: Berkeley Lab director navigates uncertain times with a focus on research" (Press release). SPIE Newsroom. May 30, 2014. doi:10.1117/2.321405.05.

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Lawrence Berkeley National Laboratory - Wikipedia

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Lawrence Berkeley National Laboratory ( LBNL), commonly referred to as Berkeley Lab, is a United States national laboratory that is owned by, and conducts scientific research on behalf of, the United States Department of Energy. Located in the hills of Berkeley, California, the lab overlooks the campus of the University of California, Berkeley, and is managed by the University of California system.

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LBNL if you use octal, 'lawrence berkeley national laboratory' 

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LBNL if you use octal, 'lawrence berkeley national laboratory' 

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hypothetical "element of atomic number zero"

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Neutronium (sometimes shortened to neutrium, also referred to as neutrite) is a hypothetical substance composed purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 (before the 1932 discovery of the neutron) for the hypothetical "element of atomic number zero" (with zero protons in its nucleus) that he placed at the head of the periodic table (denoted by -, or Nu). However, the meaning of the term has changed over time, and from the last half of the 20th century onward it has been also used to refer to extremely dense substances resembling the neutron-degenerate matter theorized to exist in the cores of neutron stars; hereinafter " degenerate neutronium" will refer to this.

Neutronium is used in popular physics literature to refer to the material present in the cores of neutron stars (stars which are too massive to be supported by electron degeneracy pressure and which collapse into a denser phase of matter). This term is very rarely used in scientific literature, for three reasons: there are multiple definitions for the term "neutronium"; there is considerable uncertainty over the composition of the material in the cores of neutron stars (it could be neutron-degenerate matter, strange matter, quark matter, or a variant or combination of the above); the properties of neutron star material should depend on depth due to changing pressure (see below), and no sharp boundary between the crust (consisting primarily of atomic nuclei) and almost protonless inner layer is expected to exist.[citation needed ]

When neutron star core material is presumed to consist mostly of free neutrons, it is typically referred to as neutron-degenerate matter in scientific literature.

The term "neutronium" was coined in 1926 by Andreas von Antropoff for a conjectured form of matter made up of neutrons with no protons or electrons, which he placed as the chemical element of atomic number zero at the head of his new version of the periodic table. It was subsequently placed in the middle of several spiral representations of the periodic system for classifying the chemical elements, such as those of Charles Janet (1928), E. I. Emerson (1944), and John D. Clark (1950).

Although the term is not used in the scientific literature either for a condensed form of matter, or as an element, there have been reports that, besides the free neutron, there may exist two bound forms of neutrons without protons. If neutronium were considered to be an element, then these neutron clusters could be considered to be the isotopes of that element. However, these reports have not been further substantiated.

Mononeutron: An isolated neutron undergoes beta decay with a mean lifetime of approximately 15 minutes (half-life of approximately 10 minutes), becoming a proton (the nucleus of hydrogen), an electron, and an antineutrino.

Dineutron: The dineutron, containing two neutrons, was unambiguously observed in 2012 in the decay of beryllium-16. It is not a bound particle, but had been proposed as an extremely short-lived resonance state produced by nuclear reactions involving tritium. It has been suggested to have a transitory existence in nuclear reactions produced by helions (completely ionized helium-3 nuclei) that result in the formation of a proton and a nucleus having the same atomic number as the target nucleus but a mass number two units greater. The dineutron hypothesis had been used in nuclear reactions with exotic nuclei for a long time. Several applications of the dineutron in nuclear reactions can be found in review papers. Its existence has been proven to be relevant for nuclear structure of exotic nuclei. A system made up of only two neutrons is not bound, though the attraction between them is very nearly enough to make them so. This has some consequences on nucleosynthesis and the abundance of the chemical elements.

Trineutron: A trineutron state consisting of three bound neutrons has not been detected, and is not expected to exist[citation needed ] even for a short time.

Tetraneutron: A tetraneutron is a hypothetical particle consisting of four bound neutrons. Reports of its existence have not been replicated.

Pentaneutron: Calculations indicate that the hypothetical pentaneutron state, consisting of a cluster of five neutrons, would not be bound.

Although not called "neutronium", the National Nuclear Data Center's Nuclear Wallet Cards lists as its first "isotope" an "element" with the symbol n and atomic number Z = 0 and mass number A = 1. This "isotope" is described as decaying to hydrogen-1 with a half life of 10.24±0.2 min.

Neutron matter is equivalent to a chemical element with atomic number 0, which is to say that it is equivalent to a species of atoms having no protons in their atomic nuclei. It is extremely radioactive; its only legitimate equivalent isotope, the free neutron, has a half-life of 10 minutes, which is approximately half that of the most stable known isotope of francium. Neutron matter decays quickly into hydrogen. Neutron matter has no electronic structure on account of its total lack of electrons.

While this lifetime is long enough to permit the study of neutronium's chemical properties, there are serious practical problems. Having no charge or electrons, neutronium would not interact strongly with ordinary low-energy photons (visible light) and would feel no electrostatic forces, so it would diffuse into the walls of most containers made of ordinary matter. Certain materials are able to resist diffusion or absorption of ultracold neutrons due to nuclear-quantum effects, specifically reflection caused by the strong interaction. At ambient temperature and in the presence of other elements, thermal neutrons readily undergo neutron capture to form heavier (and often radioactive) isotopes of that element.

Neutron matter at standard pressure and temperature is predicted by the ideal gas law to be less dense than even hydrogen, with a density of only (roughly 27 times less dense than air and half as dense as hydrogen gas). Neutron matter is expected to remain gaseous down to absolute zero at normal pressures, as the zero-point energy of the system is too high to allow condensation. However, neutron matter should in theory form a degenerate gaseous superfluid at these temperatures, composed of transient neutron-pairs called dineutrons. Under extremely low pressure, this low temperature, gaseous superfluid should exhibit quantum coherence producing a Bose-Einstein condensate. At higher temperatures, neutron matter will only condense with sufficient pressure, and solidify with even greater pressure. Such pressures exist in neutron stars, where the extreme pressure causes the neutron matter to become degenerate. However, in the presence of atomic matter compressed to the state of electron degeneracy, β − decay may be inhibited due to the Pauli exclusion principle, thus making free neutrons stable. Also, elevated pressures should make neutrons degenerate themselves.

Compared to ordinary elements, neutronium should be more compressible due to the absence of electrically charged protons and electrons. This makes neutronium more energetically favorable than (positive- Z) atomic nuclei and leads to their conversion to (degenerate) neutronium through electron capture, a process that is believed to occur in stellar cores in the final seconds of the lifetime of massive stars, where it is facilitated by cooling via emission. As a result, degenerate neutronium can have a density of [citation needed ], roughly 14 orders of magnitude denser than the densest known ordinary substances. It was theorized that extreme pressures of order might deform the neutrons into a cubic symmetry, allowing tighter packing of neutrons, or cause a strange matter formation.

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Neutronium (sometimes shortened to neutrium,[1] also referred to as neutrite[2]) is a hypothetical substance composed purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 (before the 1932 discovery of the neutron) for the hypothetical “element of atomic number zero” (wi…

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The first elements to have more than 32 electrons in one shell would belong to the g-block of period 8 of the periodic table.

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The electron shells are labeled K, L, M, N, O, P, and Q; or 1, 2, 3, 4, 5, 6, and 7; going from innermost shell outwards. Electrons in outer shells have higher average energy and travel farther from the nucleus than those in inner shells.

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Hydrogen is the chemical element with the symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all baryonic mass. Non- remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium (name rarely used, symbol ¹H), has one proton and no neutrons.

The universal emergence of atomic hydrogen first occurred during the recombination epoch ( Big Bang). At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, highly combustible diatomic gas with the molecular formula H ₂. Since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays a particularly important role in acid-base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a negative charge (i.e., anion) when it is known as a hydride, or as a positively charged (i.e., cation) species denoted by the symbol H⁺. The hydrogen cation is written as though composed of a bare proton, but in reality, hydrogen cations in ionic compounds are always more complex. As the only neutral atom for which the Schrödinger equation can be solved analytically, study of the energetics and bonding of the hydrogen atom has played a key role in the development of quantum mechanics.

Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. In 1766-81, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance, and that it produces water when burned, the property for which it was later named: in Greek, hydrogen means "water-former".

Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing (e.g., hydrocracking) and ammonia production, mostly for the fertilizer market. Hydrogen is problematic in metallurgy because it can embrittle many metals, complicating the design of pipelines and storage tanks.

Properties

Combustion

Hydrogen gas ( dihydrogen or molecular hydrogen) is highly flammable:

The enthalpy of combustion is −286 kJ/mol:

Hydrogen gas forms explosive mixtures with air in concentrations from 4-74% and with chlorine at 5-95%. The explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C (932 °F).

Pure hydrogen-oxygen flames emit ultraviolet light and with high oxygen mix are nearly invisible to the naked eye, as illustrated by the faint plume of the Space Shuttle Main Engine, compared to the highly visible plume of a Space Shuttle Solid Rocket Booster, which uses an ammonium perchlorate composite. The detection of a burning hydrogen leak may require a flame detector; such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames. The destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a rich mixture of hydrogen to oxygen combined with carbon compounds from the airship skin.[citation needed ]

H ₂ is relatively unreactive. The thermodynamic basis of this low reactivity is the very strong H-H bond, with a bond dissociation energy of 435.7 kJ/mol. The kinetic basis of the low reactivity is the nonpolar nature of H ₂ and its weak polarizability. It spontaneously reacts with chlorine and fluorine to form hydrogen chloride and hydrogen fluoride, respectively. The reactivity of H ₂ is strongly affected by the presence of metal catalysts. Thus, while H ₂ combusts readily, mixtures of H ₂ and O ₂ do not react in the absence of a catalyst.

Electron energy levels

The ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength.

The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, which conceptualizes the electron as "orbiting" the proton in analogy to the Earth's orbit of the Sun. However, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. Because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies.

A more accurate description of the hydrogen atom comes from a purely quantum mechanical treatment that uses the Schrödinger equation, Dirac equation or Feynman path integral formulation to calculate the probability density of the electron around the proton. The most complicated treatments allow for the small effects of special relativity and vacuum polarization. In the quantum mechanical treatment, the electron in a ground state hydrogen atom has no angular momentum at all-illustrating how the "planetary orbit" differs from electron motion.

Elemental molecular forms

Molecular H ₂ exists as two spin isomers, i.e. compounds with two nuclear spin states. In the orthohydrogen form, the spins of the two nuclei are parallel and form a triplet state with a molecular spin quantum number of 1 (​+​); in the parahydrogen form the spins are antiparallel and form a singlet with a molecular spin quantum number of 0 (​-​). At standard temperature and pressure, hydrogen gas contains about 25% of the para form and 75% of the ortho form, also known as the "normal form". The equilibrium ratio of orthohydrogen to parahydrogen depends on temperature, but because the ortho form is an excited state and has a higher energy than the para form, it is unstable and cannot be purified. At very low temperatures, the equilibrium state is composed almost exclusively of the para form. The liquid and gas phase thermal properties of pure parahydrogen differ significantly from those of the normal form because of differences in rotational heat capacities, as discussed more fully in spin isomers of hydrogen. The ortho/para distinction also occurs in other hydrogen-containing molecules or functional groups, such as water and methylene, but is of little significance for their thermal properties.

The ortho form converts to the para form slowly at low temperatures. The ortho/para ratio in condensed H ₂ is an important consideration in the preparation and storage of liquid hydrogen: the conversion from ortho to para is exothermic and produces enough heat to evaporate some of the hydrogen liquid, leading to loss of liquefied material. Catalysts for the ortho-para interconversion, such as ferric oxide, activated carbon, platinized asbestos, rare earth metals, uranium compounds, chromic oxide, or some nickel compounds, are used during hydrogen cooling.

Covalent and organic compounds

While H ₂ is not very reactive under standard conditions, it does form compounds with most elements. Hydrogen can form compounds with elements that are more electronegative, such as halogens (F, Cl, Br, I), or oxygen; in these compounds hydrogen takes on a partial positive charge. When bonded to a more electronegative element, particularly fluorine, oxygen, or nitrogen, hydrogen can participate in a form of medium-strength noncovalent bonding with another electronegative element with a lone pair, a phenomenon called hydrogen bonding that is critical to the stability of many biological molecules. Hydrogen also forms compounds with less electronegative elements, such as metals and metalloids, where it takes on a partial negative charge. These compounds are often known as hydrides.

Hydrogen forms a vast array of compounds with carbon called the hydrocarbons, and an even vaster array with heteroatoms that, because of their general association with living things, are called organic compounds. The study of their properties is known as organic chemistry and their study in the context of living organisms is known as biochemistry. By some definitions, "organic" compounds are only required to contain carbon. However, most of them also contain hydrogen, and because it is the carbon-hydrogen bond that gives this class of compounds most of its particular chemical characteristics, carbon-hydrogen bonds are required in some definitions of the word "organic" in chemistry. Millions of hydrocarbons are known, and they are usually formed by complicated pathways that seldom involve elemental hydrogen.

Hydrogen is highly soluble in many rare earth and transition metals and is soluble in both nanocrystalline and amorphous metals. Hydrogen solubility in metals is influenced by local distortions or impurities in the crystal lattice. These properties may be useful when hydrogen is purified by passage through hot palladium disks, but the gas's high solubility is a metallurgical problem, contributing to the embrittlement of many metals, complicating the design of pipelines and storage tanks.

Compounds of hydrogen are often called hydrides, a term that is used fairly loosely. The term "hydride" suggests that the H atom has acquired a negative or anionic character, denoted H −, and is used when hydrogen forms a compound with a more electropositive element. The existence of the hydride anion, suggested by Gilbert N. Lewis in 1916 for group 1 and 2 salt-like hydrides, was demonstrated by Moers in 1920 by the electrolysis of molten lithium hydride (LiH), producing a stoichiometric quantity of hydrogen at the anode. For hydrides other than group 1 and 2 metals, the term is quite misleading, considering the low electronegativity of hydrogen. An exception in group 2 hydrides is , which is polymeric. In lithium aluminium hydride, the anion carries hydridic centers firmly attached to the Al(III).

Although hydrides can be formed with almost all main-group elements, the number and combination of possible compounds varies widely; for example, more than 100 binary borane hydrides are known, but only one binary aluminium hydride. Binary indium hydride has not yet been identified, although larger complexes exist.

In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is particularly common in group 13 elements, especially in boranes ( boron hydrides) and aluminium complexes, as well as in clustered carboranes.

Protons and acids

Oxidation of hydrogen removes its electron and gives , which contains no electrons and a nucleus which is usually composed of one proton. That is why is often called a proton. This species is central to discussion of acids. Under the Brønsted-Lowry acid-base theory, acids are proton donors, while bases are proton acceptors.

A bare proton, , cannot exist in solution or in ionic crystals because of its unstoppable attraction to other atoms or molecules with electrons. Except at the high temperatures associated with plasmas, such protons cannot be removed from the electron clouds of atoms and molecules, and will remain attached to them. However, the term 'proton' is sometimes used loosely and metaphorically to refer to positively charged or cationic hydrogen attached to other species in this fashion, and as such is denoted "" without any implication that any single protons exist freely as a species.

To avoid the implication of the naked "solvated proton" in solution, acidic aqueous solutions are sometimes considered to contain a less unlikely fictitious species, termed the " hydronium ion" (HO). However, even in this case, such solvated hydrogen cations are more realistically conceived as being organized into clusters that form species closer to H. Other oxonium ions are found when water is in acidic solution with other solvents.

Although exotic on Earth, one of the most common ions in the universe is the ion, known as protonated molecular hydrogen or the trihydrogen cation.

Atomic hydrogen

NASA has investigated the use of atomic hydrogen as a rocket propellant. It could be stored in liquid helium to prevent it from recombining into molecular hydrogen. When the helium is vaporized, the atomic hydrogen would be released and combine back to molecular hydrogen. The result would be an intensely hot stream of hydrogen and helium gas. The liftoff weight of rockets could be reduced by 50% by this method.

Most interstellar hydrogen is in the form of atomic hydrogen because the atoms can seldom collide and combine. They are the source of the important 21 cm hydrogen line in astronomy at 1420 MHz.

Hydrogen has three naturally occurring isotopes, denoted , and . Other, highly unstable nuclei ( to ) have been synthesized in the laboratory but not observed in nature.

is the most common hydrogen isotope, with an abundance of more than 99.98%. Because the nucleus of this isotope consists of only a single proton, it is given the descriptive but rarely used formal name protium.

, the other stable hydrogen isotope, is known as and contains one proton and one neutron in the nucleus. All deuterium in the universe is thought to have been produced at the time of the Big Bang, and has endured since that time. Deuterium is not radioactive, and does not represent a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for -NMR spectroscopy. Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial nuclear fusion.

is known as and contains one proton and two neutrons in its nucleus. It is radioactive, decaying into helium-3 through beta decay with a half-life of 12.32 years. It is so radioactive that it can be used in luminous paint, making it useful in such things as watches. The glass prevents the small amount of radiation from getting out. Small amounts of tritium are produced naturally by the interaction of cosmic rays with atmospheric gases; tritium has also been released during nuclear weapons tests. It is used in nuclear fusion reactions, as a tracer in isotope geochemistry, and in specialized self-powered lighting devices. Tritium has also been used in chemical and biological labeling experiments as a radiolabel.

Unique among the elements, distinct names are assigned to its isotopes in common use today. During the early study of radioactivity, various heavy radioactive isotopes were given their own names, but such names are no longer used, except for deuterium and tritium. The symbols D and T (instead of and ) are sometimes used for deuterium and tritium, but the corresponding symbol for protium, P, is already in use for phosphorus and thus is not available for protium. In its nomenclatural guidelines, the International Union of Pure and Applied Chemistry (IUPAC) allows any of D, T, , and to be used, although and are preferred.

The exotic atom muonium (symbol Mu), composed of an antimuon and an electron, is also sometimes considered as a light radioisotope of hydrogen, due to the mass difference between the antimuon and the electron. Muonium was discovered in 1960. During the muon's lifetime, muonium can enter into compounds such as muonium chloride (MuCl) or sodium muonide (NaMu), analogous to hydrogen chloride and sodium hydride respectively.

Discovery and use

In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by naming the gas from a metal-acid reaction "inflammable air". He speculated that "inflammable air" was in fact identical to the hypothetical substance called " phlogiston" and further finding in 1781 that the gas produces water when burned. He is usually given credit for the discovery of hydrogen as an element. In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek ὑδρο- hydro meaning "water" and -γενής genes meaning "creator") when he and Laplace reproduced Cavendish's finding that water is produced when hydrogen is burned.

Lavoisier produced hydrogen for his experiments on mass conservation by reacting a flux of steam with metallic iron through an incandescent iron tube heated in a fire. Anaerobic oxidation of iron by the protons of water at high temperature can be schematically represented by the set of following reactions:

Many metals such as zirconium undergo a similar reaction with water leading to the production of hydrogen.

Hydrogen was liquefied for the first time by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask. He produced solid hydrogen the next year. Deuterium was discovered in December 1931 by Harold Urey, and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant, and Paul Harteck. Heavy water, which consists of deuterium in the place of regular hydrogen, was discovered by Urey's group in 1932. François Isaac de Rivaz built the first de Rivaz engine, an internal combustion engine powered by a mixture of hydrogen and oxygen in 1806. Edward Daniel Clarke invented the hydrogen gas blowpipe in 1819. The Döbereiner's lamp and limelight were invented in 1823.

The first hydrogen-filled balloon was invented by Jacques Charles in 1783. Hydrogen provided the lift for the first reliable form of air-travel following the 1852 invention of the first hydrogen-lifted airship by Henri Giffard. German count Ferdinand von Zeppelin promoted the idea of rigid airships lifted by hydrogen that later were called Zeppelins; the first of which had its maiden flight in 1900. Regularly scheduled flights started in 1910 and by the outbreak of World War I in August 1914, they had carried 35,000 passengers without a serious incident. Hydrogen-lifted airships were used as observation platforms and bombers during the war.

The first non-stop transatlantic crossing was made by the British airship in 1919. Regular passenger service resumed in the 1920s and the discovery of helium reserves in the United States promised increased safety, but the U.S. government refused to sell the gas for this purpose. Therefore, H ₂ was used in the Hindenburg airship, which was destroyed in a midair fire over New Jersey on 6 May 1937. The incident was broadcast live on radio and filmed. Ignition of leaking hydrogen is widely assumed to be the cause, but later investigations pointed to the ignition of the aluminized fabric coating by static electricity. But the damage to hydrogen's reputation as a lifting gas was already done and commercial hydrogen airship travel ceased. Hydrogen is still used, in preference to non-flammable but more expensive helium, as a lifting gas for weather balloons.

In the same year, the first hydrogen-cooled turbogenerator went into service with gaseous hydrogen as a coolant in the rotor and the stator in 1937 at Dayton, Ohio, by the Dayton Power & Light Co.; because of the thermal conductivity and very low viscosity of hydrogen gas, thus lower drag than air, this is the most common type in its field today for large generators (typically 60 MW and bigger; smaller generators are usually air-cooled).

The nickel hydrogen battery was used for the first time in 1977 aboard the U.S. Navy's Navigation technology satellite-2 (NTS-2). For example, the ISS, Mars Odyssey and the Mars Global Surveyor are equipped with nickel-hydrogen batteries. In the dark part of its orbit, the Hubble Space Telescope is also powered by nickel-hydrogen batteries, which were finally replaced in May 2009, more than 19 years after launch and 13 years beyond their design life.

Role in quantum theory

Because of its simple atomic structure, consisting only of a proton and an electron, the hydrogen atom, together with the spectrum of light produced from it or absorbed by it, has been central to the development of the theory of atomic structure. Furthermore, study of the corresponding simplicity of the hydrogen molecule and the corresponding cation brought understanding of the nature of the chemical bond, which followed shortly after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.

One of the first quantum effects to be explicitly noticed (but not understood at the time) was a Maxwell observation involving hydrogen, half a century before full quantum mechanical theory arrived. Maxwell observed that the specific heat capacity of H ₂ unaccountably departs from that of a diatomic gas below room temperature and begins to increasingly resemble that of a monatomic gas at cryogenic temperatures. According to quantum theory, this behavior arises from the spacing of the (quantized) rotational energy levels, which are particularly wide-spaced in H ₂ because of its low mass. These widely spaced levels inhibit equal partition of heat energy into rotational motion in hydrogen at low temperatures. Diatomic gases composed of heavier atoms do not have such widely spaced levels and do not exhibit the same effect.

Antihydrogen () is the antimatter counterpart to hydrogen. It consists of an antiproton with a positron. Antihydrogen is the only type of antimatter atom to have been produced as of 2015.

Cosmic prevalence and distribution

Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75 percent of normal matter by mass and more than 90 percent by number of atoms. (Most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as dark matter and dark energy.) This element is found in great abundance in stars and gas giant planets. Molecular clouds of H ₂ are associated with star formation. Hydrogen plays a vital role in powering stars through the proton-proton reaction in case of stars with very low to approximately 1 mass of the Sun and the CNO cycle of nuclear fusion in case of stars more massive than our Sun.

Throughout the universe, hydrogen is mostly found in the atomic and plasma states, with properties quite distinct from those of molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity and high emissivity (producing the light from the Sun and other stars). The charged particles are highly influenced by magnetic and electric fields. For example, in the solar wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen is found in the neutral atomic state in the interstellar medium. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the universe up to redshift z=4.

Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H ₂. However, hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases. However, hydrogen is the third most abundant element on the Earth's surface, mostly in the form of chemical compounds such as hydrocarbons and water. Hydrogen gas is produced by some bacteria and algae and is a natural component of flatus, as is methane, itself a hydrogen source of increasing importance.

A molecular form called protonated molecular hydrogen () is found in the interstellar medium, where it is generated by ionization of molecular hydrogen from cosmic rays. This ion has also been observed in the upper atmosphere of the planet Jupiter. The ion is relatively stable in the environment of outer space due to the low temperature and density. is one of the most abundant ions in the universe, and it plays a notable role in the chemistry of the interstellar medium. Neutral triatomic hydrogen H ₃ can exist only in an excited form and is unstable. By contrast, the positive hydrogen molecular ion () is a rare molecule in the universe.

Production

is produced in chemistry and biology laboratories, often as a by-product of other reactions; in industry for the hydrogenation of unsaturated substrates; and in nature as a means of expelling reducing equivalents in biochemical reactions.

Electrolysis of water

The electrolysis of water is a simple method of producing hydrogen. A low voltage current is run through the water, and gaseous oxygen forms at the anode while gaseous hydrogen forms at the cathode. Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage. If, however, the gas is to be burnt on site, oxygen is desirable to assist the combustion, and so both electrodes would be made from inert metals. (Iron, for instance, would oxidize, and thus decrease the amount of oxygen given off.) The theoretical maximum efficiency (electricity used vs. energetic value of hydrogen produced) is in the range 88-94%.

Methane pyrolysis (industrial method)

Hydrogen production using natural gas methane pyrolysis is a recent "no greenhouse gas" one-step process. Developing volume production using this method is the key to enabling faster carbon reduction by using hydrogen in industrial processes, fuel cell electric heavy truck transportation, and in gas turbine electric power generation. Methane pyrolysis uses methane bubbled up through the molten metal catalyst at high temperatures (1340 K, 1065 °C or 1950 °F) to produce non-polluting hydrogen gas in high volume, at low cost and produces non-polluting solid carbon C with no emission of greenhouse gas.

The industrial quality carbon may be sold as manufacturing feedstock or permanently landfilled. Methane pyrolysis is in development and considered suitable for commercial bulk hydrogen production. Volume production is being evaluated in the BASF "methane pyrolysis at scale" pilot plant. Further research continues in several laboratories, including at Karlsruhe Liquid-metal Laboratory (KALLA) and the chemical engineering laboratory at University of California - Santa Barbara

Steam reforming (industrial method)

Hydrogen is often produced using natural gas, which involves the removal of hydrogen from hydrocarbons at very high temperatures, with 48% of hydrogen production coming from steam reforming. Commercial bulk hydrogen is usually produced by the steam reforming of natural gas with release of atmospheric greenhouse gas or with capture using CCS and climate change mitigation. Steam reforming is also known as the Bosch process and is widely used for the industrial preparation of hydrogen.

At high temperatures (1000-1400 K, 700-1100 °C or 1300-2000 °F), steam (water vapor) reacts with methane to yield carbon monoxide and .

This reaction is favored at low pressures but is nonetheless conducted at high pressures (2.0 MPa, 20 atm or 600 inHg). This is because high-pressure is the most marketable product, and pressure swing adsorption (PSA) purification systems work better at higher pressures. The product mixture is known as " synthesis gas" because it is often used directly for the production of methanol and related compounds. Hydrocarbons other than methane can be used to produce synthesis gas with varying product ratios. One of the many complications to this highly optimized technology is the formation of coke or carbon:

Consequently, steam reforming typically employs an excess of . Additional hydrogen can be recovered from the steam by use of carbon monoxide through the water gas shift reaction, especially with an iron oxide catalyst. This reaction is also a common industrial source of carbon dioxide:

Other important methods for CO and production include partial oxidation of hydrocarbons:

and the coal reaction, which can serve as a prelude to the shift reaction above:

Hydrogen is sometimes produced and consumed in the same industrial process, without being separated. In the Haber process for the production of ammonia, hydrogen is generated from natural gas. Electrolysis of brine to yield chlorine also produces hydrogen as a co-product.

Many metals react with water to produce , but the rate of hydrogen evolution depends on the metal, the pH, and the presence alloying agents. Most commonly, hydrogen evolution is induced by acids. The alkali and alkaline earth metals, aluminium, zinc, manganese, and iron react readily with aqueous acids. This reaction is the basis of the Kipp's apparatus, which once was used as a laboratory gas source:

In the absence of acid, the evolution of is slower. Because iron is widely used structural material, its anaerobic corrosion is of technological significance:

Many metals, such as aluminium, are slow to react with water because they form passivated coatings of oxides. An alloy of aluminium and gallium, however, does react with water. At high pH, aluminium can produce :

Some metal-containing compounds react with acids to evolve . Under anaerobic conditions, ferrous hydroxide () can be oxidized by the protons of water to form magnetite and . This process is described by the Schikorr reaction:

This process occurs during the anaerobic corrosion of iron and steel in oxygen-free groundwater and in reducing soils below the water table.

Thermochemical

More than 200 thermochemical cycles can be used for water splitting. Many of these cycles such as the iron oxide cycle, cerium(IV) oxide-cerium(III) oxide cycle, zinc zinc-oxide cycle, sulfur-iodine cycle, copper-chlorine cycle and hybrid sulfur cycle have been evaluated for their commercial potential to produce hydrogen and oxygen from water and heat without using electricity. A number of laboratories (including in France, Germany, Greece, Japan, and the USA) are developing thermochemical methods to produce hydrogen from solar energy and water.

Serpentinization reaction

In deep geological conditions prevailing far away from the Earth's atmosphere, hydrogen () is produced during the process of serpentinization. In this process, water protons (H⁺) are reduced by ferrous (Fe ²⁺) ions provided by fayalite (FeSiO). The reaction forms magnetite (FeO), quartz (Si), and hydrogen ():

This reaction closely resembles the Schikorr reaction observed in anaerobic oxidation of ferrous hydroxide in contact with water.

Applications

Petrochemical industry

Large quantities of are used in the "upgrading" of fossil fuels. Key consumers of include hydrodealkylation, hydrodesulfurization, and hydrocracking. Many of these reactions can be classified as hydrogenolysis, i.e., the cleavage of bonds to carbon. Illustrative is the separation of sulfur from liquid fossil fuels:

Hydrogenation

Hydrogenation, the addition of to various substrates is conducted on a large scale. The hydrogenation of N2 to produce ammonia by the Haber-Bosch Process consumes a few percent of the energy budget in the entire industry. The resulting ammonia is used to supply the majority of the protein consumed by humans. Hydrogenation is used to convert unsaturated fats and oils to saturated fats and oils. The major application is the production of margarine. Methanol is produced by hydrogenation of carbon dioxide. It is similarly the source of hydrogen in the manufacture of hydrochloric acid. is also used as a reducing agent for the conversion of some ores to the metals.

Hydrogen is commonly used in power stations as a coolant in generators due to a number of favorable properties that are a direct result of its light diatomic molecules. These include low density, low viscosity, and the highest specific heat and thermal conductivity of all gases.

Energy carrier

Hydrogen is not an energy resource as a combustion fuel because there is no naturally occurring source of hydrogen in useful quantities. The Sun's energy comes from nuclear fusion of hydrogen, but this process is difficult to achieve controllably on Earth. Elemental hydrogen from solar, biological, or electrical sources requires more energy to make than is obtained by burning it, so in these cases hydrogen functions as an energy carrier, like a battery. Hydrogen may be obtained from fossil sources (such as methane), but these sources are unsustainable.

The energy density per unit volume of both liquid hydrogen and compressed hydrogen gas at any practicable pressure is significantly less than that of traditional fuel sources, although the energy density per unit fuel mass is higher. Nevertheless, elemental hydrogen has been widely discussed in the context of energy, as a possible future carrier of energy on an economy-wide scale. For example, sequestration followed by carbon capture and storage could be conducted at the point of production from fossil fuels. Hydrogen used in transportation would burn relatively cleanly, with some emissions, but without carbon emissions. However, the infrastructure costs associated with full conversion to a hydrogen economy would be substantial. Fuel cells can convert hydrogen and oxygen directly to electricity more efficiently than internal combustion engines.

Semiconductor industry

Niche and evolving uses

Apart from its use as a reactant, has a variety of smaller applications. It is used as a shielding gas in welding methods such as atomic hydrogen welding. H ₂ is used as the rotor coolant in electrical generators at power stations, because it has the highest thermal conductivity of any gas. Liquid H ₂ is used in cryogenic research, including superconductivity studies. Because is lighter than air, having a little more than ​ of the density of air, it was once widely used as a lifting gas in balloons and airships.

Pure or mixed with nitrogen (sometimes called forming gas), hydrogen is a tracer gas for detection of minute leaks. Applications can be found in the automotive, chemical, power generation, aerospace, and telecommunications industries. Hydrogen is an authorized food additive (E 949) that allows food package leak testing among other anti-oxidizing properties.

Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects. Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints.

The triple point temperature of equilibrium hydrogen is a defining fixed point on the ITS-90 temperature scale at 13.8033 Kelvin.

Biological reactions

H ₂ is a product of some types of anaerobic metabolism and is produced by several microorganisms, usually via reactions catalyzed by iron- or nickel-containing enzymes called hydrogenases. These enzymes catalyze the reversible redox reaction between H ₂ and its component two protons and two electrons. Creation of hydrogen gas occurs in the transfer of reducing equivalents produced during pyruvate fermentation to water. The natural cycle of hydrogen production and consumption by organisms is called the hydrogen cycle. Hydrogen is the most abundant element in the human body in terms of numbers of atoms of the element but, it is the 3rd most abundant element by mass, because hydrogen is so light. H ₂ occurs in the breath of humans due to the metabolic activity of hydrogenase-containing microorganisms in the large intestine. The concentration in fasted people at rest is typically less than 5 Parts per million (ppm) but can be 50 ppm when people with intestinal disorders consume molecules they cannot absorb during diagnostic hydrogen breath tests.

Water splitting, in which water is decomposed into its component protons, electrons, and oxygen, occurs in the light reactions in all photosynthetic organisms. Some such organisms, including the alga Chlamydomonas reinhardtii and cyanobacteria, have evolved a second step in the dark reactions in which protons and electrons are reduced to form H ₂ gas by specialized hydrogenases in the chloroplast. Efforts have been undertaken to genetically modify cyanobacterial hydrogenases to efficiently synthesize H ₂ gas even in the presence of oxygen. Efforts have also been undertaken with genetically modified alga in a bioreactor.

Safety and precautions

Hydrogen poses a number of hazards to human safety, from potential detonations and fires when mixed with air to being an asphyxiant in its pure, oxygen-free form. In addition, liquid hydrogen is a cryogen and presents dangers (such as frostbite) associated with very cold liquids. Hydrogen dissolves in many metals and in addition to leaking out, may have adverse effects on them, such as hydrogen embrittlement, leading to cracks and explosions. Hydrogen gas leaking into external air may spontaneously ignite. Moreover, hydrogen fire, while being extremely hot, is almost invisible, and thus can lead to accidental burns.

Even interpreting the hydrogen data (including safety data) is confounded by a number of phenomena. Many physical and chemical properties of hydrogen depend on the parahydrogen/orthohydrogen ratio (it often takes days or weeks at a given temperature to reach the equilibrium ratio, for which the data is usually given). Hydrogen detonation parameters, such as critical detonation pressure and temperature, strongly depend on the container geometry.

1. However, most of the universe's mass is not in the form of baryons or chemical elements. See ^ dark matter and dark energy.

2. ^ 286 kJ/mol: energy per mole of the combustible material (molecular hydrogen).

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Further reading

External links

# data[].attributes.attachment_link.description
Hydrogen is the chemical element with the symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all baryonic mass.

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Periodic table of the chemical elements showing the most or more commonly named sets of elements (in periodic tables), and a traditional dividing line between metals and nonmetals. The f-block actually fits between groups 2 and 3; it is usually shown at the foot of the table to save space.

The periodic table, also known as the periodic table of the elements, arranges the chemical elements into rows (" periods") and columns (" groups"). It is an organizing icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which says that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics.

Vertical, horizontal and diagonal trends characterize the periodic table. Metallic character increases going down a group and decreases from left to right across a period. Nonmetallic character increases going from the bottom left of the periodic table to the top right.

The first periodic table to become generally accepted was that of the Russian chemist Dmitri Mendeleev in 1869; he formulated the periodic law as a dependence of chemical properties on atomic mass. As not all elements were then known, there were gaps in his periodic table, and Mendeleev successfully used the periodic law to predict some properties of some of the missing elements. The periodic law was recognized as a fundamental discovery in the late 19th century. It was explained early in the 20th century, with the discovery of atomic numbers and associated pioneering work in quantum mechanics both ideas serving to illuminate the internal structure of the atom. A recognisably modern form of the table was reached in 1945 with Glenn T. Seaborg's discovery that the actinides were in fact f-block rather than d-block elements. The periodic table and law are now a central and indispensable part of modern chemistry.

The periodic table continues to evolve with the progress of science. In nature, only elements up to atomic number 94 exist; to go further, it was necessary to synthesise new elements in the laboratory. Today, while all the first 118 elements are known, thereby completing the first seven rows of the table, chemical characterisation is still needed for the heaviest elements to confirm that their properties match their positions. It is not yet known how far the table will go beyond these seven rows and whether the patterns of the known part of the table will continue into this unknown region. Some scientific discussion also continues regarding whether some elements are correctly positioned in today's table. Many alternative representations of the periodic law exist, and there is some discussion as to whether there is an optimal form of the periodic table.

Each chemical element has a unique atomic number ( Z) representing the number of protons in its nucleus. Most elements have multiple isotopes, variants with the same number of protons but different numbers of neutrons. For example, carbon has three naturally occurring isotopes: all of its atoms have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. When atomic mass is shown, it is usually the weighted average of naturally occurring isotopes; but if there are none, the mass of the most stable isotope usually appears, often in parentheses.

In the standard periodic table, the elements are listed in order of increasing atomic number Z. A new row (period) is started when a new electron shell has its first electron. Columns (groups) are determined by the electron configuration of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. oxygen and selenium are in the same column because they both have four electrons in the outermost p-subshell). Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.

The first 94 elements occur naturally; the remaining 24, americium to oganesson (95-118), occur only when synthesized in laboratories. Of the 94 naturally occurring elements, 83 are primordial and 11 occur only in decay chains of primordial elements. No element heavier than einsteinium (element 99) has ever been observed in macroscopic quantities in its pure form, nor has astatine (element 85); francium (element 87) has been only photographed in the form of light emitted from microscopic quantities (300,000 atoms).

Group names and numbers

Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases). The f-block groups are ignored in this numbering. Groups can also be named by their first element, e.g. the "scandium group" for group 3. Previously, groups were known by Roman numerals. In America, the Roman numerals were followed by either an "A" if the group was in the s- or p-block, or a "B" if the group was in the d-block. The Roman numerals used correspond to the last digit of today's naming convention (e.g. the group 4 elements were group IVB, and the group 14 elements were group IVA). In Europe, the lettering was similar, except that "A" was used if the group was before group 10, and "B" was used for groups including and after group 10. In addition, groups 8, 9 and 10 used to be treated as one triple-sized group, known collectively in both notations as group VIII. In 1988, the new IUPAC (International Union of Pure and Applied Chemistry) naming system (1-18) was put into use, and the old group names (I-VIII) were deprecated.

Presentation forms

For reasons of space, the periodic table is commonly presented with the f-block elements cut out and positioned placed as a distinct part below the main body. It reduces the number of element columns from 32 to 18.

Both forms represent the same periodic table. The form with the f-block included in the main body is sometimes called the 32-column or long form; the form with the f-block cut out the 18-column or medium-long form. The 32-column form has the advantage of showing all elements in their correct sequence, but it has the disadvantage of requiring more space. The form chosen is an editorial choice, and does not imply any change of scientific claim or statement. For example, when discussing the composition of group 3, the options can be shown equally (unprejudiced) in both forms.

Periodic tables usually at least show the elements' symbols; many also provide supplementary information about the elements, either via colour-coding or as data in the cells. The above table shows the names and atomic numbers of the elements, and also their blocks, natural occurrences and standard atomic weights. For the short-lived elements without standard atomic weights, the mass number of the most stable known isotope is used instead. Other tables may include properties such as state of matter, melting and boiling points, densities, as well as provide different classifications of the elements.

Atomic structures of the elements

The nucleus and its surrounding electrons

3D views of some hydrogen-like atomic orbitals showing probability density and phase (g orbitals and higher are not shown)

The smallest constituents of all normal matter are known as atoms. Atoms are extremely small, being about one ten-billionth of a meter across; thus their internal structure is governed by quantum mechanics. Atoms consist of a small positively charged nucleus, made of positively charged protons and uncharged neutrons, surrounded by a cloud of negatively charged electrons; the charges cancel out, so atoms are neutral. Electrons participate in chemical reactions, but the nucleus does not. When atoms participate in chemical reactions, they either gain or lose electrons to form positively- or negatively-charged ions; or share electrons with each other.

Atoms can be subdivided into different types based on the number of protons (and thus also electrons) they have. This is called the atomic number, often symbolised Z  (for "Zahl" - German for "number"). Each distinct atomic number therefore corresponds to a class of atom: these classes are called the chemical elements. The chemical elements are what the periodic table classifies and organises. Hydrogen is the element with atomic number 1; helium, atomic number 2; lithium, atomic number 3; and so on. Each of these names can be further abbreviated by a one- or two-letter chemical symbol; those for hydrogen, helium, and lithium are respectively H, He, and Li. Neutrons do not affect the atom's chemical identity, but do affect its weight. Atoms with the same number of protons but different numbers of neutrons are called isotopes of the same chemical element. Naturally occurring elements usually occur as mixes of different isotopes; since each isotope usually occurs with a characteristic abundance, naturally occurring elements have well-defined atomic weights, defined as the average mass of a naturally occurring atom of that element.

Today, 118 elements are known, the first 94 of which are known to occur naturally on Earth at present. Of the 94 natural elements, eighty have a stable isotope and one more ( bismuth) has an almost-stable isotope (with a half-life over a billion times the age of the universe). Two more, thorium and uranium, have isotopes undergoing radioactive decay with a half-life comparable to the age of the Earth. The stable elements plus bismuth, thorium, and uranium make up the 83 primordial elements that survived from the Earth's formation. The remaining eleven natural elements decay quickly enough that their continued trace occurrence rests primarily on being constantly regenerated as intermediate products of the decay of thorium and uranium. All 24 known artificial elements are radioactive.

Electron configurations

The periodic table is a graphic description of the periodic law, which states that the properties and atomic structures of the chemical elements are a periodic function of their atomic number. Elements are placed in the periodic table according to their electron configurations, the periodic recurrences of which explain the trends in properties across the periodic table.

An electron can be thought of as inhabiting an atomic orbital, which characterises the probability it can be found in any particular region around the atom. Their energies are quantised, which is to say that they can only take discrete values. Furthermore, electrons obey the Pauli exclusion principle: different electrons must always be in different states. This allows classification of the possible states an electron can take in various energy levels known as shells, divided into individual subshells, which each contain one or more orbitals. Each orbital can contain up to two electrons: they are distinguished by a quantity known as spin, conventionally labeled "up" or "down". In a cold atom (one in its ground state), electrons arrange themselves in such a way that the total energy they have is minimised by occupying the lowest-energy orbitals available. Only the outermost electrons (so-called valence electrons) have enough energy to break free of the nucleus and participate in chemical reactions with other atoms. The others are called core electrons.

Elements are known with up to the first seven shells occupied. The first shell contains only one orbital, a spherical s orbital. As it is in the first shell, this is called the 1s orbital. This can hold up to two electrons. The second shell similarly contains a 2s orbital, and it also contains three dumbbell-shaped 2p orbitals, and can thus fill up to eight electrons (2×1 + 2×3 = 8). The third shell contains one 3s orbital, three 3p orbitals, and five 3d orbitals, and thus has a capacity of 2×1 + 2×3 + 2×5 = 18. The fourth shell contains one 4s orbital, three 4p orbitals, five 4d orbitals, and seven 4f orbitals, thus leading to a capacity of 2×1 + 2×3 + 2×5 + 2×7 = 32. Higher shells contain more types of orbitals that continue the pattern, but such types of orbitals are not filled in the ground states of known elements. The subshell types are characterised by the quantum numbers. Four numbers describe an orbital in an atom completely: the principal quantum number n, the azimuthal quantum number ℓ (the orbital type), the magnetic quantum number m ℓ, and the spin quantum number s.

The order of subshell filling

Idealized order of subshell filling according to the Madelung rule

The sequence in which the subshells are filled is given in most cases by the Aufbau principle, also known as the Madelung or Klechkovsky rule (after Erwin Madelung and Vsevolod Klechkovsky respectively). This rule was first observed empirically by Madelung, and Klechkovsky and later authors gave it theoretical justification. The shells overlap in energies, and the Madelung rule specifies the sequence of filling according to:

1s ≪ 2s < 2p ≪ 3s < 3p ≪ 4s < 3d < 4p ≪ 5s < 4d < 5p ≪ 6s < 4f < 5d < 6p ≪ 7s < 5f < 6d < 7p ≪ ...

Here the sign ≪ means "much less than" as opposed to < meaning just "less than". Phrased differently, electrons enter orbitals in order of increasing n + ℓ, and if two orbitals are available with the same value of n + ℓ, the one with lower n is occupied first. In general, orbitals with the same value of n + ℓ are similar in energy, but in the case of the s-orbitals (with ℓ = 0), quantum effects raise their energy to approach that of the next n + ℓ group. Hence the periodic table is usually drawn to begin each row (often called a period) with the filling of a new s-orbital, which corresponds to the beginning of a new shell. Thus, with the exception of the first row, each period length appears twice:

The overlaps get quite close at the point where the d-orbitals enter the picture, and the order can shift slightly with atomic number and atomic charge.

Starting from the simplest atom, this lets us build up the periodic table one at a time in order of atomic number, by considering the cases of single atoms. In hydrogen, there is only one electron, which must go in the lowest-energy orbital 1s. This electron configuration is written 1s ¹, where the superscript indicates the number of electrons in the subshell. Helium adds a second electron, which also goes into 1s, completely filling the first shell and giving the configuration 1s ².

Starting from the third element, lithium, the first shell is full, so its third electron occupies a 2s orbital, giving a 1s ² 2s ¹ configuration. The 2s electron is lithium's only valence electron, as the 1s subshell is now too tightly bound to the nucleus to participate in chemical bonding to other atoms. Thus the filled first shell is called a " core shell" for this and all heavier elements. The 2s subshell is completed by the next element beryllium (1s ² 2s ²). The following elements then proceed to fill the 2p subshell. Boron (1s ² 2s ² 2p ¹) puts its new electron in a 2p orbital; carbon (1s ² 2s ² 2p ²) fills a second 2p orbital; and with nitrogen (1s ² 2s ² 2p ³) all three 2p orbitals become singly occupied. This is consistent with Hund's rule, which states that atoms usually prefer to singly occupy each orbital of the same type before filling them with the second electron. Oxygen (1s ² 2s ² 2p ⁴), fluorine (1s ² 2s ² 2p ⁵), and neon (1s ² 2s ² 2p ⁶) then complete the already singly filled 2p orbitals; the last of these fills the second shell completely.

Starting from element 11, sodium, the second shell is full, making the second shell a core shell for this and all heavier elements. The eleventh electron begins the filling of the third shell by occupying a 3s orbital, giving a configuration of 1s ² 2s ² 2p ⁶ 3s ¹ for sodium. This configuration is abbreviated [Ne] 3s ¹, where [Ne] represents neon's configuration. Magnesium ([Ne] 3s ²) finishes this 3s orbital, and the following six elements aluminium, silicon, phosphorus, sulfur, chlorine, and argon fill the three 3p orbitals ([Ne] 3s ² 3p ¹ through [Ne] 3s ² 3p ⁶). This creates an analogous series in which the outer shell structures of sodium through argon are analogous to those of lithium through neon, and is the basis for the periodicity of chemical properties that the periodic table illustrates: at regular but changing intervals of atomic numbers, the properties of the chemical elements approximately repeat.

The first eighteen elements can thus be arranged as the start of a periodic table. Elements in the same column have the same number of valence electrons and have analogous valence electron configurations: these columns are called groups. The single exception is helium, which has two valence electrons like beryllium and magnesium, but is typically placed in the column of neon and argon to emphasise that its outer shell is full. (Some contemporary authors question even this single exception, preferring to consistently follow the valence configurations and place helium over beryllium.) There are eight columns in this periodic table fragment, corresponding to at most eight outer-shell electrons. A period begins when a new shell starts filling. Finally, the colouring illustrates the blocks: the elements in the s-block (coloured red) are filling s-orbitals, while those in the p-block (coloured yellow) are filling p-orbitals.

Starting the next row, for potassium and calcium the 4s subshell is the lowest in energy, and therefore they fill it. Potassium adds one electron to the 4s shell ([Ar] 4s ¹), and calcium then completes it ([Ar] 4s ²). However, starting from scandium ([Ar] 3d ¹ 4s ²) the 3d subshell becomes the next highest in energy. The 4s and 3d subshells have approximately the same energy and they compete for filling the electrons, and so the occupation is not quite consistently filling the 3d orbitals one at a time. The precise energy ordering of 3d and 4s changes along the row, and also changes depending on how many electrons are removed from the atom. For example, due to the repulsion between the 3d electrons and the 4s ones, at chromium the 4s energy level becomes slightly higher than 3d, and so it becomes more profitable to have a [Ar] 3d ⁵ 4s ¹ configuration than an [Ar] 3d ⁴ 4s ² one. A similar anomaly occurs at copper. These are violations of the Madelung rule. Such anomalies however do not have any chemical significance, as the various configurations are so close in energy to each other that the presence of a nearby atom can shift the balance. The periodic table therefore ignores these and considers only idealised configurations.

At zinc ([Ar] 3d ¹⁰ 4s ²), the 3d orbitals are completely filled with a total of ten electrons. Next come the 4p orbitals, completing the row, which are filled progressively by gallium ([Ar] 3d ¹⁰ 4s ² 4p ¹) through krypton ([Ar] 3d ¹⁰ 4s ² 4p ⁶), in a manner analogous to the previous p-block elements. From gallium onwards, the 3d orbitals form part of the electronic core, and no longer participate in chemistry. The s- and p-block elements, which fill their outer shells, are called main-group elements; the d-block elements (coloured blue below), which fill an inner shell, are called transition elements (or transition metals, since they are all metals).

The next eighteen elements fill the 5s orbitals ( rubidium and strontium), then 4d ( yttrium through cadmium, again with a few anomalies along the way), and then 5p ( indium through xenon). Again, from indium onward the 4d orbitals are in the core. Hence the fifth row has the same structure as the fourth.

The sixth row of the table likewise starts with two s-block elements: caesium and barium. After this, the first f-block elements (coloured green below) begin to appear, starting with lanthanum. These are sometimes termed inner transition elements. As there are now not only 4f but also 5d and 6s subshells at similar energies, competition occurs once again with many irregular configurations; this resulted in some dispute about where exactly the f-block is supposed to begin, but most who study the matter agree that it starts at lanthanum in accordance with the Aufbau principle. Even though lanthanum does not itself fill the 4f subshell as a single atom, because of repulsion between electrons, its 4f orbitals are low enough in energy to participate in chemistry. At ytterbium, the seven 4f orbitals are completely filled with fourteen electrons; thereafter, a series of ten transition elements ( lutetium through mercury) follows, and finally six main-group elements ( thallium through radon) complete the period. From lutetium onwards the 4f orbitals are in the core, and from thallium onwards so are the 5d orbitals.

The seventh row is analogous to the sixth row: 7s fills ( francium and radium), then 5f ( actinium to nobelium), then 6d ( lawrencium to copernicium), and finally 7p ( nihonium to oganesson). Starting from lawrencium the 5f orbitals are in the core, and probably the 6d orbitals join the core starting from nihonium. Again there are a few anomalies along the way: for example, as single atoms neither actinium nor thorium actually fills the 5f subshell, and lawrencium does not fill the 6d shell, but all these subshells can still become filled in chemical environments. For a very long time, the seventh row was incomplete as most of its elements do not occur in nature. The missing elements beyond uranium started to be synthesised in the laboratory in 1940, when neptunium was made. The row was completed with the synthesis of tennessine in 2010 (the last element oganesson had already been made in 2002), and the last elements in this seventh row were given names in 2016.

This completes the modern periodic table, with all seven rows completely filled to capacity.

Electron configuration table

The following table shows the electron configuration of a neutral gas-phase atom of each element. Different configurations can be favoured in different chemical environments. The main-group elements have entirely regular electron configurations; the transition and inner transition elements show twenty irregularities due to the aforementioned competition between subshells close in energy level. For the last ten elements (109-118), experimental data is lacking and therefore calculated configurations have been shown instead. Completely filled subshells have been greyed out.

Variations

Although the modern periodic table is standard today, the placement of the period 1 elements hydrogen and helium remains an open issue under discussion, and some variation can be found. Following electron configurations, hydrogen would be placed in group 1, and helium would be placed in group 2. The group 1 placement of hydrogen is common, but helium is almost always placed in group 18 with the other noble gases. The debate has to do with conflicting understandings of the extent to which chemical or electronic properties should decide periodic table placement.

Like the group 1 metals, hydrogen has one electron in its outermost shell and typically loses its only electron in chemical reactions. Hydrogen has some metal-like chemical properties, being able to displace some metals from their salts. But it forms a diatomic nonmetallic gas at standard conditions, unlike the alkali metals which are reactive solid metals. This and hydrogen's formation of hydrides, in which it gains an electron, brings it close to the properties of the halogens which do the same (though it is rarer for hydrogen to form H − than H⁺). Moreover, the lightest two halogens ( fluorine and chlorine) are gaseous like hydrogen at standard conditions. Some properties of hydrogen are not a good fit for either group: hydrogen is neither highly oxidising nor highly reducing and is not reactive with water. Hydrogen thus has properties corresponding to both those of the alkali metals and the halogens, but matches neither group perfectly, and is thus difficult to place by its chemistry. Therefore, while the electronic placement of hydrogen in group 1 predominates, some rarer arrangements show either hydrogen in group 17, duplicate hydrogen in both groups 1 and 17, or float it separately from all groups. This last option has nonetheless been criticised by the chemist and philosopher of science Eric Scerri on the grounds that it appears to imply that hydrogen is above the periodic law altogether, unlike all the other elements.

Helium is the only element that routinely occupies a position in the periodic table that is not consistent with its electronic structure. It has two electrons in its outermost shell, whereas the other noble gases have eight; and it is an s-block element, whereas all other noble gases are p-block elements. However it is unreactive at standard conditions, and has a full outer shell: these properties are like the noble gases in group 18, but not at all like the reactive alkaline earth metals of group 2. For these reasons helium is nearly universally placed in group 18 which its properties best match; a proposal to move helium to group 2 was rejected by IUPAC in 1988 for these reasons. Nonetheless, helium is still occasionally placed in group 2 today, and some of its physical and chemical properties are closer to the group 2 elements and support the electronic placement. Solid helium crystallises in a hexagonal close-packed structure, which matches beryllium and magnesium in group 2, but not the other noble gases in group 18. Recent theoretical developments in noble gas chemistry, in which helium is expected to show less inertness than neon and to form (HeO)(LiF) ₂ with a structure similar to the analogous beryllium compound (but with no expected neon analogue), have resulted in more chemists advocating a placement of helium in group 2. The first-row anomaly in the periodic table is cited in support of this reassignment, since helium as the first s-block element before the alkaline earth metals stands out as anomalous in a way that helium as the first noble gas does not. For example, a large difference in atomic radii between the first and second members of each main group is seen in groups 1 and 13-17: it exists between neon and argon, and between helium and beryllium, but not between helium and neon. Moving helium to group 2 makes this trend consistent in groups 2 and 18 as well. Tables that float both hydrogen and helium outside all groups may rarely be encountered.

Group 3: Sc, Y, Lu, Lr

Group 3: Sc, Y, La, Ac

In many periodic tables, the f-block is shifted one element to the right, so that lanthanum and actinium become d-block elements in group 3, and Ce-Lu and Th-Lr form the f-block thereby splitting the d-block into two very uneven portions. This is a holdover from early mistaken measurements of electron configurations. The 4f shell is completely filled at ytterbium, and for that reason Lev Landau and Evgeny Lifshitz in 1948 considered it incorrect to group lutetium as an f-block element. They did not yet take the step of removing lanthanum from the d-block as well, but Jun Kondō realised in 1963 that lanthanum's low-temperature superconductivity implied the activity of its 4f shell. In 1965, David C. Hamilton linked this observation to its position in the periodic table, and argued that the f-block should be composed of the elements La-Yb and Ac-No. Since then, physical, chemical, and electronic evidence has supported this assignment, as shown here and as supported by IUPAC reports dating from 1988 (when the 1-18 group numbers were recommended) and 2021. The variation nonetheless still exists because most textbook writers are not aware of the issue. A third form can sometimes be encountered in which the spaces below yttrium in group 3 are left empty, such as the table appearing on the IUPAC web site, but this is inconsistent with quantum mechanics by making the f-block 15 elements wide (La-Lu and Ac-Lr) even though only 14 electrons can fit in an f-subshell.

Several arguments in favour of Sc-Y-La-Ac can be encountered in the literature, but they have been challenged as being logically inconsistent. For example, it has been argued that lanthanum and actinium cannot be f-block elements because their atoms have not begun to fill the f-subshells. But the same is true of thorium which is never disputed as an f-block element, and this argument overlooks the problem on the other end: that the f-shells complete filling at ytterbium and nobelium (matching the Sc-Y-Lu-Lr form), not at lutetium and lawrencium (as in Sc-Y-La-Ac). Such exceptions have in any case never been considered as relevant for positioning any other elements on the periodic table. The relevant fact for placement is that lanthanum and actinium (like thorium) have valence f-orbitals that can become occupied in chemical environments, whereas lutetium and lawrencium do not. Thus the relationship between yttrium and lanthanum is only a secondary relationship between elements with the same number of valence electrons but different kinds of valence orbitals, such as that between chromium and uranium; whereas the relationship between yttrium and lutetium is primary, sharing both valence electron count and valence orbital type.

Periodic trends

As chemical reactions involve the valence electrons, elements with similar outer electron configurations may be expected to react similarly and form compounds with similar proportions of elements in them. Such elements are placed in the same group, and thus there tend to be clear similarities and trends in chemical behaviour as one proceeds down a group. As analogous configurations occur at regular intervals, the properties of the elements thus exhibit periodic recurrences, hence the name of the periodic table and the periodic law. These periodic recurrences were noticed well before the underlying theory that explains them was developed.

Atomic radius

Historically, the physical size of atoms was unknown until the early 20th century. The first calculated estimate of the atomic radius of hydrogen was published by physicist Artur Haas in 1910 to within an order of magnitude (a factor of 10) of the accepted value, the Bohr radius (~0.529 Å). In his model, Haas used a single-electron configuration based on the classical atomic model proposed by J. J. Thomson in 1904, often called the plum-pudding model.

Atomic radii (the size of atoms) are dependent on the sizes of their outermost orbitals. They generally decrease going left to right along the main-group elements, because the nuclear charge increases but the outer electrons are still in the same shell. However, going down a column, the radii generally increase, because the outermost electrons are in higher shells that are thus further away from the nucleus. The first row of each block is abnormally small, due to an effect called kainosymmetry or primogenic repulsion: the 1s, 2p, 3d, and 4f subshells have no inner analogues to which they would be orthogonal. Higher s-, p-, d-, and f-subshells experience strong repulsion from their inner analogues, which have approximately the same angular distribution of charge, and must expand to avoid this. This makes significant differences arise between the small 2p elements, which prefer multiple bonding, and the larger 3p and higher p-elements, which do not. Similar anomalies arise for the 1s, 2p, 3d, 4f, and the hypothetical 5g elements: the degree of this first-row anomaly is highest for the s-block, is moderate for the p-block, and is less pronounced for the d- and f-blocks.

In the transition elements, an inner shell is filling, but the size of the atom is still determined by the outer electrons. The increasing nuclear charge across the series and the increased number of inner electrons for shielding somewhat compensate each other, so the decrease in radius is smaller. The 4p and 5d atoms, coming immediately after new types of transition series are first introduced, are smaller than would have been expected, because the added core 3d and 4f subshells provide only incomplete shielding of the nuclear charge for the outer electrons. Hence for example gallium atoms are slightly smaller than aluminium atoms. Together with kainosymmetry, this results in an even-odd difference between the periods (except in the s-block) that is sometimes known as secondary periodicity: elements in even periods have smaller atomic radii and prefer to lose fewer electrons, while elements in odd periods (except the first) differ in the opposite direction. Thus for example many properties in the p-block show a zigzag rather than a smooth trend along the group. For example, phosphorus and antimony in odd periods of group 15 readily reach the +5 oxidation state, whereas nitrogen, arsenic, and bismuth in even periods prefer to stay at +3.

Thallium and lead atoms are about the same size as indium and tin atoms respectively, but from bismuth to radon the 6p atoms are larger than the analogous 5p atoms. This happens because when atomic nuclei become highly charged, special relativity becomes needed to gauge the effect of the nucleus on the electron cloud. These relativistic effects result in heavy elements increasingly having differing properties compared to their lighter homologues in the periodic table. Spin-orbit interaction splits the p-subshell: one p-orbital is relativistically stabilised and shrunken (it fills in thallium and lead), but the other two (filling in bismuth through radon) are relativistically destabilised and expanded. Relativistic effects also explain why gold is golden and mercury is a liquid at room temperature. They are expected to become very strong in the late seventh period, potentially leading to a collapse of periodicity. Electron configurations are only clearly known until element 108 ( hassium), and experimental chemistry beyond 108 has only been done for 112 ( copernicium), 113 ( nihonium), and 114 ( flerovium), so the chemical characterisation of the heaviest elements remains a topic of current research.

Ionisation energy

The first ionisation energy of an atom is the energy required to remove an electron from it. This varies with the atomic radius: ionisation energy increases left to right and down to up, because electrons that are closer to the nucleus are held more tightly and are more difficult to remove. Ionisation energy thus is minimised at the first element of each period - hydrogen and the alkali metals - and then generally rises until it reaches the noble gas at the right edge of the period. There are some exceptions to this trend, such as oxygen, where the electron being removed is paired and thus interelectronic repulsion makes it easier to remove than expected.

In the transition series, the outer electrons are preferentially lost even though the inner orbitals are filling. For example, in the 3d series, the 4s electrons are lost first even though the 3d orbitals are being filled. The shielding effect of adding an extra 3d electron approximately compensates the rise in nuclear charge, and therefore the ionisation energies stay mostly constant, though there is a small increase especially at the end of each transition series.

As metal atoms tend to lose electrons in chemical reactions, ionisation energy is generally correlated with chemical reactivity, although there are other factors involved as well.

Electron affinity

The opposite property to ionisation energy is the electron affinity, which is the energy released when adding an electron to the atom. A passing electron will be more readily attracted to an atom if it feels the pull of the nucleus more strongly, and especially if there is an available partially filled outer orbital that can accommodate it. Therefore, electron affinity tends to increase down to up and left to right. The exception is the last column, the noble gases, which have a full shell and have no room for another electron. This gives the halogens in the next-to-last column the highest electron affinities.

Some atoms, like the noble gases, have no electron affinity: they cannot form stable gas-phase anions. The noble gases, having high ionisation energies and no electron affinity, have little inclination towards gaining or losing electrons and are generally unreactive.

Some exceptions to the trends occur: oxygen and fluorine have lower electron affinities than their heavier homologues sulfur and chlorine, because they are small atoms and hence the newly added electron would experience significant repulsion from the already present ones. For the nonmetallic elements, electron affinity likewise somewhat correlates with reactivity, but not perfectly since other factors are involved. For example, fluorine has a lower electron affinity than chlorine (because of extreme interelectronic repulsion for the very small fluorine atom), but is more reactive.

Valence and oxidation states

The valence of an element can be defined either as the number of hydrogen atoms that can combine with it to form a simple binary hydride, or as twice the number of oxygen atoms that can combine with it to form a simple binary oxide (that is, not a peroxide or a superoxide). The valences of the main-group elements are directly related to the group number: the hydrides in the main groups 1-2 and 13-17 follow the formulae MH, MH ₂, MH ₃, MH ₄, MH ₃, MH ₂, and finally MH. The highest oxides instead increase in valence, following the formulae M ₂O, MO, M ₂O ₃, MO ₂, M ₂O ₅, MO ₃, M ₂O ₇. Today the notion of valence has been extended by that of the oxidation state, which is the formal charge left on an element when all other elements in a compound have been removed as their ions.

The electron configuration suggests a ready explanation from the number of electrons available for bonding, although a full explanation requires considering the energy that would be released in forming compounds with different valences rather than simply considering electron configurations alone. For example, magnesium forms Mg ²⁺ rather than Mg⁺ cations when dissolved in water, because the latter would spontaneously disproportionate into Mg ⁰ and Mg ²⁺ cations. This is because the enthalpy of hydration (surrounding the cation with water molecules) increases in magnitude with the charge and radius of the ion. In Mg⁺, the outermost orbital (which determines ionic radius) is still 3s, so the hydration enthalpy is small and insufficient to compensate the energy required to remove the electron; but ionising again to Mg ²⁺ uncovers the core 2p subshell, making the hydration enthalpy large enough to allow magnesium(II) compounds to form. For similar reasons, the common oxidation states of the heavier p-block elements (where the ns electrons become lower in energy than the np) tend to vary by steps of 2, because that is necessary to uncover an inner subshell and decrease the ionic radius (e.g. Tl⁺ uncovers 6s, and Tl ³⁺ uncovers 5d, so once thallium loses two electrons it tends to lose the third one as well). Analogous arguments based on orbital hybridisation can be used for the less electronegative p-block elements.

For transition metals, common oxidation states are nearly always at least +2 for similar reasons (uncovering the next subshell); this holds even for the metals with anomalous d x+1s ¹ or d x+2s ⁰ configurations (except for silver), because repulsion between d-electrons means that the movement of the second electron from the s- to the d-subshell does not appreciably change its ionisation energy. Because ionising the transition metals further does not uncover any new inner subshells, their oxidation states tend to vary by steps of 1 instead. The lanthanides and late actinides generally show a stable +3 oxidation state, removing the outer s-electrons and then (usually) one electron from the (n−2)f-orbitals, that are similar in energy to ns. The common and maximum oxidation states of the d- and f-block elements tend to depend on the ionisation energies. As the energy difference between the (n−1)d and ns orbitals rises along each transition series, it becomes less energetically favourable to ionise further electrons. Thus, the early transition metal groups tend to prefer higher oxidation states, but the +2 oxidation state becomes more stable for the late transition metal groups. The highest formal oxidation state thus increases from +3 at the beginning of each d-block row, to +7 or +8 in the middle (e.g. ), and then to +2 at the end. The lanthanides and late actinides usually have high fourth ionisation energies and hence rarely surpass the +3 oxidation state, whereas early actinides have low fourth ionisation energies and so for example neptunium and plutonium can reach +7.

As elements in the same group share the same valence configurations, they usually exhibit similar chemical behaviour. For example, the alkali metals in the first group all have one valence electron, and form a very homogeneous class of elements: they are all soft and reactive metals. However, there are many factors involved, and groups can often be rather hetereogeneous. For instance, hydrogen also has one valence electron and is in the same group as the alkali metals, but its chemical behaviour is quite different. The stable elements of group 14 comprise a nonmetal ( carbon), two semiconductors ( silicon and germanium), and two metals ( tin and lead); they are nonetheless united by having four valence electrons. This often leads to similarities in maximum and minimum oxidation states (e.g. sulfur and selenium in group 16 both have maximum oxidation state +6, as in and , and minimum oxidation state −2, as in sulfides and selenides); but not always (e.g. oxygen is not known to form oxidation state +6, despite being in the same group as sulfur and selenium).

Electronegativity

Another important property of elements is their electronegativity. Atoms can form covalent bonds to each other by sharing electrons in pairs, creating an overlap of valence orbitals. The degree to which each atom attracts the shared electron pair depends on the atom's electronegativity - the tendency of an atom towards gaining or losing electrons. The more electronegative atom will tend to attract the electron pair more, and the less electronegative (or more electropositive) one will attract it less. In extreme cases, the electron can be thought of as having been passed completely from the more electropositive atom to the more electronegative one, though this is a simplification. The bond then binds two ions, one positive (having given up the electron) and one negative (having accepted it), and is termed an ionic bond.

Electronegativity depends on how strongly the nucleus can attract an electron pair, and so it exhibits a similar variation to the other properties already discussed: electronegativity tends to fall going up to down, and rise going left to right. The alkali and alkaline earth metals are among the most electropositive elements, while the chalcogens, halogens, and noble gases are among the most electronegative ones.

Electronegativity is generally measured on the Pauling scale, on which the most electronegative reactive atom ( fluorine) is given electronegativity 4.0, and the least electronegative atom ( caesium) is given electronegativity 0.79. In fact neon is the most electronegative element, but the Pauling scale cannot measure its electronegativity because it does not form covalent bonds with most elements.

An element's electronegativity varies with the identity and number of the atoms it is bonded to, as well as how many electrons it has already lost: an atom becomes more electronegative when it has lost more electrons. This sometimes makes a large difference: lead in the +2 oxidation state has electronegativity 1.87 on the Pauling scale, while lead in the +4 oxidation state has electronegativity 2.33.

A simple substance is a substance formed from atoms of one chemical element. The simple substances of the more electronegative atoms tend to share electrons (form covalent bonds) with each other. They form either small molecules (like hydrogen or oxygen, whose atoms bond in pairs) or giant structures stretching indefinitely (like carbon or silicon). The noble gases simply stay as single atoms, as they already have a full shell. Substances composed of discrete molecules or single atoms are held together by weaker attractive forces between the molecules, such as the London dispersion force: as electrons move within the molecules, they create momentary imbalances of electrical charge, which induce similar imbalances on nearby molecules and create synchronised movements of electrons across many neighbouring molecules.

The more electropositive atoms, however, tend to instead lose electrons, creating a "sea" of electrons engulfing cations. The outer orbitals of one atom overlap to share electrons with all its neighbours, creating a giant structure of molecular orbitals extending over all the atoms. This negatively charged "sea" pulls on all the ions and keeps them together in a metallic bond. Elements forming such bonds are often called metals; those which do not are often called nonmetals. Some elements can form multiple simple substances with different structures: these are called allotropes. For example, diamond and graphite are two allotropes of carbon.

The metallicity of an element can be predicted from electronic properties. When atomic orbitals overlap during metallic or covalent bonding, they create both bonding and antibonding molecular orbitals of equal capacity, with the antibonding orbitals of higher energy. Net bonding character occurs when there are more electrons in the bonding orbitals than there are in the antibonding orbitals. Metallic bonding is thus possible when the number of electrons delocalised by each atom is less than twice the number of orbitals contributing to the overlap. This is the situation for elements in groups 1 through 13; they also have too few valence electrons to form giant covalent structures where all atoms take equivalent positions, and so almost all of them metallise. The exceptions are hydrogen and boron, which have too high an ionisation energy. Hydrogen thus forms a covalent H ₂ molecule, and boron forms a giant covalent structure based on icosahedral B ₁₂ clusters. In a metal, the bonding and antibonding orbitals have overlapping energies, creating a single band that electrons can freely flow through, allowing for electrical conduction.

In group 14, both metallic and covalent bonding become possible. In a diamond crystal, covalent bonds between carbon atoms are strong, because they have a small atomic radius and thus the nucleus has more of a hold on the electrons. Therefore, the bonding orbitals that result are much lower in energy than the antibonding orbitals, and there is no overlap, so electrical conduction becomes impossible: carbon is a nonmetal. However, covalent bonding becomes weaker for larger atoms and the energy gap between the bonding and antibonding orbitals decreases. Therefore, silicon and germanium have smaller band gaps and are semiconductors: electrons can cross the gap when thermally excited. The band gap disappears in tin, so that tin and lead become metals.

Elements in groups 15 through 17 have too many electrons to form giant covalent molecules that stretch in all three dimensions. For the lighter elements, the bonds in small diatomic molecules are so strong that a condensed phase is disfavoured: thus nitrogen (N ₂), oxygen (O ₂), white phosphorus and yellow arsenic (P ₄ and As ₄), sulfur and red selenium (S ₈ and Se ₈), and the stable halogens (F ₂, Cl ₂, Br ₂, and I ₂) readily form covalent molecules with few atoms. The heavier ones tend to form long chains (e.g. red phosphorus, grey selenium, tellurium) or layered structures (e.g. carbon as graphite, black phosphorus, grey arsenic, grey antimony, bismuth) that only extend in one or two rather than three dimensions. Both kinds of structures can be found as allotropes of phosphorus, arsenic, and selenium, although the long-chained allotropes are more stable in all three. As these structures do not use all their orbitals for bonding, they end up with bonding, nonbonding, and antibonding bands in order of increasing energy. Similarly to group 14, the band gaps shrink for the heavier elements and free movement of electrons between the chains or layers becomes possible. Thus for example black phosphorus, black arsenic, grey selenium, tellurium, and iodine are semiconductors; grey arsenic, grey antimony, and bismuth are semimetals (exhibiting quasi-metallic conduction, with a very small band overlap); and polonium and probably astatine are true metals. Finally, the natural group 18 elements all stay as individual atoms.

The dividing line between metals and nonmetals is roughly diagonal from top left to bottom right, with the transition series appearing to the left of this diagonal (as they have many available orbitals for overlap). This is expected, as metallicity tends to be correlated with electropositivity and the willingness to lose electrons, which increases right to left and up to down. Thus the metals greatly outnumber the nonmetals. Elements near the borderline are difficult to classify: they tend to have properties that are intermediate between those of metals and nonmetals, and may have some properties characteristic of both. They are often termed semimetals or metalloids. The term "semimetal" used in this sense should not be confused with its strict physical sense having to do with band structure: bismuth is physically a semimetal, but is generally considered a metal by chemists.

The following table considers the most stable allotropes at standard conditions. The elements coloured yellow form simple substances that are well-characterised by metallic bonding. Elements coloured light blue form giant network covalent structures, whereas those coloured dark blue form small covalently bonded molecules that are held together by weaker van der Waals forces. The noble gases are coloured in violet: their molecules are single atoms and no covalent bonding occurs. Greyed-out cells are for elements which have not been prepared in sufficient quantities for their most stable allotropes to have been characterised in this way. Theoretical considerations and current experimental evidence suggest that all of those elements would metallise if they could form condensed phases, except perhaps for oganesson.

Arsenic, an element often called a semi-metal or metalloid

Generally, metals are shiny and dense. They usually have high melting and boiling points due to the strength of the metallic bond, and are often malleable and ductile (easily stretched and shaped) because the atoms can move relative to each other without breaking the metallic bond. They conduct electricity because their electrons are free to move in all three dimensions. Similarly, they conduct heat, which is transferred by the electrons as extra kinetic energy: they move faster. These properties persist in the liquid state, as although the crystal structure is destroyed on melting, the atoms still touch and the metallic bond persists, though it is weakened. Metals tend to be reactive towards nonmetals. Some exceptions can be found to these generalisations: for example, manganese, arsenic, antimony, and bismuth are brittle; chromium is extremely hard; gallium, rubidium, caesium, and mercury are liquid at or close to room temperature; and noble metals such as gold are chemically very inert.

Nonmetals exhibit different properties. Those forming giant covalent crystals exhibit high melting and boiling points, as it takes considerable energy to overcome the strong covalent bonds. Those forming discrete molecules are held together mostly by dispersion forces, which are more easily overcome; thus they tend to have lower melting and boiling points, and many are liquids or gases at room temperature. Nonmetals are often dull-looking. They tend to be reactive towards metals, except for the noble gases, which are inert towards most substances. They are brittle when solid as their atoms are held tightly in place. They are less dense and conduct electricity poorly, because there are no mobile electrons. Near the borderline, band gaps are small and thus many elements in that region are semiconductors, such as silicon, germanium, selenium, and tellurium. Again there are exceptions; for example, diamond has the highest thermal conductivity of all known materials, greater than any metal.

It is common to designate a class of metalloids straddling the boundary between metals and nonmetals, as elements in that region are intermediate in both physical and chemical properties. However, no consensus exists in the literature for precisely which elements should be so designated. When such a category is used, silicon, germanium, arsenic, and tellurium are almost always included, and boron and antimony usually are; but most sources include other elements as well, without agreement on which extra elements should be added, and some others subtract from this list instead.

Further manifestations of periodicity

There are some other relationships throughout the periodic table between elements that are not in the same group, such as the diagonal relationships between elements that are diagonally adjacent (e.g. lithium and magnesium). Some similarities can also be found between the main groups and the transition metal groups, or between the early actinides and early transition metals, when the elements have the same number of valence electrons. Thus uranium somewhat resembles chromium and tungsten in group 6, as all three have six valence electrons. Relationships between elements with the same number of valence electrons but different types of valence orbital have been called secondary or isodonor relationships: they usually have the same maximum oxidation states, but not the same minimum oxidation states. For example, chlorine and manganese both have +7 as their maximum oxidation state (e.g. and ), but their respective minimum oxidation states are −1 (e.g. HCl) and −3 (K ₂[Mn(CO) ₄]). Elements with the same number of valence vacancies but different numbers of valence electrons are related by a tertiary or isoacceptor relationship: they have similar minimum but not maximum oxidation states. For example, hydrogen and chlorine both have −1 as their minimum oxidation state (in hydrides and chlorides), but hydrogen's maximum oxidation state is +1 (e.g. ) while chlorine's is +7.

Many other physical properties of the elements exhibit periodic variation in accordance with the periodic law, such as melting points, boiling points, heats of fusion, heats of vaporisation, atomisation energy, and so on. Similar periodic variations appear for the compounds of the elements, which can be observed by comparing hydrides, oxides, sulfides, halides, and so on. Chemical properties are more difficult to describe quantitatively, but likewise exhibit their own periodicities. Examples include the variation in the acidic and basic properties of the elements and their compounds, the stabilities of compounds, and methods of isolating the elements. Periodicity is and has been used very widely to predict the properties of unknown new elements and new compounds, and is central to modern chemistry.

Classification of elements

A periodic table colour-coded to show some commonly used sets of similar elements. The categories and their boundaries differ somewhat between sources.[151] Lutetium and lawrencium in group 3 are also transition metals.[54]

Many terms have been used in the literature to describe sets of elements that behave similarly. The group names alkali metal, alkaline earth metal, triel, tetrel, pnictogen, chalcogen, halogen, and noble gas are acknowledged by IUPAC; the other groups can be referred to by their number, or by their first element (e.g., group 6 is the chromium group). Some divide the p-block elements from groups 13 to 16 by metallicity, although there is neither an IUPAC definition nor a precise consensus on exactly which elements should be considered metals, nonmetals, or semi-metals (sometimes called metalloids). Neither is there a consensus on what the metals succeeding the transition metals ought to be called, with post-transition metal and poor metal being among the possibilities having been used. Some advanced monographs exclude the elements of group 12 from the transition metals on the grounds of their sometimes quite different chemical properties, but this is not a universal practice and IUPAC does not presently mention it as allowable in its Principles of Chemical Nomenclature.

The lanthanides are considered to be the elements La-Lu, which are all very similar to each other: historically they included only Ce-Lu, but lanthanum became included by common usage. The rare earth elements (or rare earth metals) add scandium and yttrium to the lanthanides. Analogously, the actinides are considered to be the elements Ac-Lr (historically Th-Lr), although variation of properties in this set is much greater than within the lanthanides. IUPAC recommends the names lanthanoids and actinoids to avoid ambiguity, as the -ide suffix typically denotes a negative ion; however lanthanides and actinides remain common. With the increasing recognition of lutetium and lawrencium as d-block elements, some authors began to define the lanthanides as La-Yb and the actinides as Ac-No, matching the f-block.

Many more categorisations exist and are used according to certain disciplines. In astrophysics, a metal is defined as any element with atomic number greater than 2, i.e. anything except hydrogen and helium. The term "semimetal" has a different definition in physics than it does in chemistry: bismuth is a semimetal by physical definitions, but chemists generally consider it a metal. A few terms are widely used, but without any very formal definition, such as " heavy metal", which has been given such a wide range of definitions that it has been criticised as "effectively meaningless".

The scope of terms varies significantly between authors. For example, according to IUPAC, the noble gases extend to include the whole group, including the very radioactive superheavy element oganesson. However, among those who specialise in the superheavy elements, this is not often done: in this case "noble gas" is typically taken to imply the unreactive behaviour of the lighter elements of the group. Since calculations generally predict that oganesson should not be particularly inert due to relativistic effects, and may not even be a gas at room temperature if it could be produced in bulk, its status as a noble gas is often questioned in this context. Furthermore, national variations are sometimes encountered: in Japan, alkaline earth metals often do not include beryllium and magnesium as their behaviour is different from the heavier group 2 metals.

Early history

In 1817, German physicist Johann Wolfgang Döbereiner began to formulate one of the earliest attempts to classify the elements. In 1829, he found that he could form some of the elements into groups of three, with the members of each group having related properties. He termed these groups triads. Chlorine, bromine, and iodine formed a triad; as did calcium, strontium, and barium; lithium, sodium, and potassium; and sulfur, selenium, and tellurium. Today, all these triads form part of modern-day groups. Various chemists continued his work and were able to identify more and more relationships between small groups of elements. However, they could not build one scheme that encompassed them all.

John Newlands published a letter in the Chemical News in February 1863 on the periodicity among the chemical elements. In 1864 Newlands published an article in the Chemical News showing that if the elements are arranged in the order of their atomic weights, those having consecutive numbers frequently either belong to the same group or occupy similar positions in different groups, and he pointed out that each eighth element starting from a given one is in this arrangement a kind of repetition of the first, like the eighth note of an octave in music (The Law of Octaves). However, Newlands' formulation only worked well for the main-group elements, and encountered serious problems with the others.

German chemist Lothar Meyer noted the sequences of similar chemical and physical properties repeated at periodic intervals. According to him, if the atomic weights were plotted as ordinates (i.e. vertically) and the atomic volumes as abscissas (i.e. horizontally)-the curve obtained a series of maximums and minimums-the most electropositive elements would appear at the peaks of the curve in the order of their atomic weights. In 1864, a book of his was published; it contained an early version of the periodic table containing 28 elements, and classified elements into six families by their valence -for the first time, elements had been grouped according to their valence. Works on organizing the elements by atomic weight had until then been stymied by inaccurate measurements of the atomic weights. In 1868, he revised his table, but this revision was published as a draft only after his death.

The definitive breakthrough came from the Russian chemist Dmitri Mendeleev. Although other chemists (including Meyer) had found some other versions of the periodic system at about the same time, Mendeleev was the most dedicated to developing and defending his system, and it was his system that most impacted the scientific community. On 17 February 1869 (1 March 1869 in the Gregorian calendar), Mendeleev began arranging the elements and comparing them by their atomic weights. He began with a few elements, and over the course of the day his system grew until it encompassed most of the known elements. After he found a consistent arrangement, his printed table appeared in May 1869 in the journal of the Russian Chemical Society. When elements did not appear to fit in the system, he boldly predicted that either valencies or atomic weights had been measured incorrectly, or that there was a missing element yet to be discovered. In 1871, Mendeleev published a long article, including an updated form of his table, that made his predictions for unknown elements explicit. Mendeleev predicted the properties of three of these unknown elements in detail: as they would be missing heavier homologues of boron, aluminium, and silicon, he named them eka-boron, eka-aluminium, and eka-silicon ("eka" being Sanskrit for "one").

In 1875, the French chemist Paul-Émile Lecoq de Boisbaudran, working without knowledge of Mendeleev's prediction, discovered a new element in a sample of the mineral sphalerite, and named it gallium. He isolated the element and began determining its properties. Mendeleev, reading de Boisbaudran's publication, sent a letter claiming that gallium was his predicted eka-aluminium. Although Lecoq de Boisbaudran was initially sceptical, and suspected that Mendeleev was trying to take credit for his discovery, he later admitted that Mendeleev was correct. In 1879, the Swedish chemist Lars Fredrik Nilson discovered a new element, which he named scandium: it turned out to be eka-boron. Eka-silicon was found in 1886 by German chemist Clemens Winkler, who named it germanium. The properties of gallium, scandium, and germanium matched what Mendeleev had predicted. In 1889, Mendeleev noted at the Faraday Lecture to the Royal Institution in London that he had not expected to live long enough "to mention their discovery to the Chemical Society of Great Britain as a confirmation of the exactitude and generality of the periodic law". Even the discovery of the noble gases at the close of the 19th century, which Mendeleev had not predicted, fitted neatly into his scheme as an eighth main group.

Mendeleev nevertheless had some trouble fitting the known lanthanides into his scheme, as they did not exhibit the periodic change in valencies that the other elements did. After much investigation, the Czech chemist Bohuslav Brauner suggested in 1902 that the lanthanides could all be placed together in one group on the periodic table. He named this the "asteroid hypothesis" as an astronomical analogy: just as there is an asteroid belt instead of a single planet between Mars and Jupiter, so the place below yttrium was thought to be occupied by all the lanthanides instead of just one element.

Atomic number

After the internal structure of the atom was probed, amateur Dutch physicist Antonius van den Broek proposed in 1913 that the nuclear charge determined the placement of elements in the periodic table. The New Zealand physicist Ernest Rutherford coined the word "atomic number" for this nuclear charge. In van der Broek's published article he illustrated the first electronic periodic table showing the elements arranged according to the number of their electrons. Rutherford confirmed in his 1914 paper that Bohr had accepted the view of van der Broek.

The same year, English physicist Henry Moseley using X-ray spectroscopy confirmed van den Broek's proposal experimentally. Moseley determined the value of the nuclear charge of each element from aluminium to gold and showed that Mendeleev's ordering actually places the elements in sequential order by nuclear charge. Nuclear charge is identical to proton count and determines the value of the atomic number ( Z) of each element. Using atomic number gives a definitive, integer-based sequence for the elements. Moseley's research immediately resolved discrepancies between atomic weight and chemical properties; these were cases such as tellurium and iodine, where atomic number increases but atomic weight decreases. Although Moseley was soon killed in World War I, the Swedish physicist Manne Siegbahn continued his work up to uranium, and established that it was the element with the highest atomic number then known (92). Based on Moseley and Siegbahn's research, it was also known which atomic numbers corresponded to missing elements yet to be found.

Electron shells

The Danish physicist Niels Bohr applied Max Planck's idea of quantisation to the atom. He concluded that the energy levels of electrons were quantised: only a discrete set of stable energy states were allowed. Bohr then attempted to understand periodicity through electron configurations, surmising in 1913 that the inner electrons should be responsible for the chemical properties of the element. In 1913, he produced the first electronic periodic table based on a quantum atom.

Bohr called his electron shells "rings" in 1913: atomic orbitals within shells did not exist at the time of his planetary model. Bohr explains in Part 3 of his famous 1913 paper that the maximum electrons in a shell is eight, writing, "We see, further, that a ring of n electrons cannot rotate in a single ring round a nucleus of charge ne unless n < 8." For smaller atoms, the electron shells would be filled as follows: "rings of electrons will only join if they contain equal numbers of electrons; and that accordingly the numbers of electrons on inner rings will only be 2, 4, 8." However, in larger atoms the innermost shell would contain eight electrons: "on the other hand, the periodic system of the elements strongly suggests that already in neon N = 10 an inner ring of eight electrons will occur." His proposed electron configurations for the atoms (shown to the right) mostly do not accord with those now known.

The first one to systematically expand and correct the chemical potentials of Bohr's atomic theory was Walther Kossel in 1914 and in 1916. Kossel explained that in the periodic table new elements would be created as electrons were added to the outer shell. In Kossel's paper, he writes: "This leads to the conclusion that the electrons, which are added further, should be put into concentric rings or shells, on each of which ... only a certain number of electrons-namely, eight in our case-should be arranged. As soon as one ring or shell is completed, a new one has to be started for the next element; the number of electrons, which are most easily accessible, and lie at the outermost periphery, increases again from element to element and, therefore, in the formation of each new shell the chemical periodicity is repeated."

In a 1919 paper, Irving Langmuir postulated the existence of "cells" which we now call orbitals, which could each only contain two electrons each, and these were arranged in "equidistant layers" which we now call shells. He made an exception for the first shell to only contain two electrons. The chemist Charles Rugeley Bury suggested in 1921 that eight and eighteen electrons in a shell form stable configurations. Bury proposed that the electron configurations in transitional elements depended upon the valence electrons in their outer shell. He introduced the word transition to describe the elements now known as transition metals or transition elements.

Prompted by Bohr, Wolfgang Pauli took up the problem of electron configurations in 1923. Pauli extended Bohr's scheme to use four quantum numbers, and formulated his exclusion principle which stated that no two electrons could have the same four quantum numbers. This explained the lengths of the periods in the periodic table (2, 8, 18, and 32), which corresponded to the number of electrons that each shell could occupy. In 1925, Friedrich Hund arrived at configurations close to the modern ones. As a result of these advances, periodicity became based on the number of chemically active or valence electrons rather than by the valences of the elements. The Aufbau principle that describes the electron configurations of the elements was first empirically observed by Erwin Madelung in 1926, though the first to publish it was Vladimir Karapetoff in 1930. In 1961, Vsevolod Klechkovsky derived the first part of the Madelung rule (that orbitals fill in order of increasing n + ℓ) from the Thomas-Fermi model; the complete rule was derived from a similar potential in 1971 by Yury N. Demkov and Valentin N. Ostrovsky.

Periodic table of Alfred Werner (1905), the first appearance of the long form[20]

The quantum theory clarified the transition metals and lanthanides as forming their own separate groups, transitional between the main groups, although some chemists had already proposed tables showing them this way before then: the English chemist Henry Bassett did so in 1892, the Danish chemist Julius Thomsen in 1895, and the Swiss chemist Alfred Werner in 1905. Bohr used Thomsen's form in his 1922 Nobel Lecture; Werner's form is very similar to the modern 32-column form. In particular, this supplanted Brauner's asteroidal hypothesis.

The exact position of the lanthanides, and thus the composition of group 3, remained under dispute for decades longer because their electron configurations were initially measured incorrectly. On chemical grounds Bassett, Werner, and Bury grouped scandium and yttrium with lutetium rather than lanthanum (the former two left an empty space below yttrium as lutetium had not yet been discovered). Hund assumed in 1927 that all the lanthanide atoms had configuration [Xe]4f 0−145d ¹6s ², on account of their prevailing trivalency (it is now known that the relationship between chemistry and electron configuration is more complicated than that). Early spectroscopic evidence seemed to confirm this, and thus the periodic table was structured to have group 3 as scandium, yttrium, lanthanum, and actinium, with fourteen f-elements breaking up the d-block between lanthanum and hafnium. But it was later discovered that this is only true for four of the fifteen lanthanides (lanthanum, cerium, gadolinium, and lutetium), and that the other lanthanide atoms do not have a d-electron. In particular, ytterbium completes the 4f shell and thus Soviet physicists Lev Landau and Evgeny Lifshitz noted in 1948 that lutetium is correctly regarded as a d-block rather than an f-block element; that bulk lanthanum is an f-metal was first suggested by Jun Kondō in 1963, on the grounds of its low-temperature superconductivity. This clarified the importance of looking at low-lying excited states of atoms that can play a role in chemical environments when classifying elements by block and positioning them on the table. Many authors subsequently rediscovered this correction based on physical, chemical, and electronic concerns and applied it to all the relevant elements, thus making group 3 contain scandium, yttrium, lutetium, and lawrencium and having lanthanum through ytterbium and actinium through nobelium as the f-block rows: this corrected version achieves consistency with the Madelung rule and vindicates Bassett, Werner, and Bury's initial chemical placement.

In 1988, IUPAC released a report supporting this composition of group 3, a decision that was reaffirmed in 2021. Variation can still be found in textbooks on the composition of group 3, and some argumentation against this format is still published today, but chemists and physicists who have considered the matter largely agree on group 3 containing scandium, yttrium, lutetium, and lawrencium and challenge the counterarguments as being inconsistent.

Synthetic elements

By 1936, the pool of missing elements from hydrogen to uranium had shrunk to four: elements 43, 61, 85, and 87 remained missing. Element 43 eventually became the first element to be synthesised artificially via nuclear reactions rather than discovered in nature. It was discovered in 1937 by Italian chemists Emilio Segrè and Carlo Perrier, who named their discovery technetium, after the Greek word for "artificial". Elements 61 ( promethium) and 85 ( astatine) were likewise produced artificially in 1945 and 1940 respectively; element 87 ( francium) became the last element to be discovered in nature, by French chemist Marguerite Perey in 1939. The elements beyond uranium were likewise discovered artificially, starting with Edwin McMillan and Philip Abelson's 1940 discovery of neptunium (via bombardment of uranium with neutrons). Glenn T. Seaborg and his team at the Lawrence Berkeley National Laboratory (LBNL) continued discovering transuranium elements, starting with plutonium in 1941, and discovered that contrary to previous thinking, the elements from actinium onwards were congeners of the lanthanides rather than transition metals. Bassett (1892), Werner (1905), and the French engineer Charles Janet (1928) had previously suggested this, but their ideas did not then receive general acceptance. Seaborg thus called them the actinides. Elements up to 101 (named mendelevium in honour of Mendeleev) were synthesised up to 1955, either through neutron or alpha-particle irradiation, or in nuclear explosions in the cases of 99 (einsteinium) and 100 (fermium).

A significant controversy arose with elements 102 through 106 in the 1960s and 1970s, as competition arose between the LBNL team (now led by Albert Ghiorso) and a team of Soviet scientists at the Joint Institute for Nuclear Research (JINR) led by Georgy Flyorov. Each team claimed discovery, and in some cases each proposed their own name for the element, creating an element naming controversy that lasted decades. These elements were made by bombardment of actinides with light ions. IUPAC at first adopted a hands-off approach, preferring to wait and see if a consensus would be forthcoming. It was also the height of the Cold War, and it became clear after some time that this would not happen. As such, IUPAC and the International Union of Pure and Applied Physics (IUPAP) created a Transfermium Working Group (TWG, fermium being element 100) in 1985 to set out criteria for discovery, which were published in 1991. After some further controversy, these elements received their final names in 1997, including seaborgium (106) in honour of Seaborg.

The TWG's criteria were used to arbitrate later element discovery claims from LBNL and JINR, as well as from research institutes in Germany ( GSI) and Japan ( Riken). Currently, consideration of discovery claims is performed by a IUPAC/IUPAP Joint Working Party. After priority was assigned, the elements were officially added to the periodic table, and the discoverers were invited to propose their names. By 2016, this had occurred for all elements up to 118, therefore completing the periodic table's first seven rows. The discoveries of elements beyond 106 were made possible by techniques devised by Yuri Oganessian at the JINR: cold fusion (bombardment of lead and bismuth by heavy ions) made possible the 1981-2004 discoveries of elements 107 through 112 at GSI and 113 at Riken, and he led the JINR team (in collaboration with American scientists) to discover elements 114 through 118 using hot fusion (bombardment of actinides by calcium ions) in 1998-2010. The heaviest known element, oganesson (118), is named in Oganessian's honour. Element 114 is named flerovium in honour of his predecessor and mentor Flyorov.

In celebration of the periodic table's 150th anniversary, the United Nations declared the year 2019 as the International Year of the Periodic Table, celebrating "one of the most significant achievements in science". The discovery criteria set down by the TWG were updated in 2020 in response to experimental and theoretical progress that had not been foreseen in 1991. Today, the periodic table is among the most recognisable icons of chemistry. IUPAC is involved today with many processes relating to the periodic table: the recognition and naming of new elements, recommending group numbers and collective names, and the updating of atomic weights.

Future extension beyond the seventh period

The most recently named elements - nihonium (113), moscovium (115), tennessine (117), and oganesson (118) - completed the seventh row of the periodic table. Future elements would have to begin an eighth row. These elements may be referred to either by their atomic numbers (e.g. " element 119"), or by the IUPAC systematic element names adopted in 1978, which directly relate to the atomic numbers (e.g. "ununennium" for element 119, derived from Latin unus "one", Greek ennea "nine", and the traditional -ium suffix for metallic elements). All attempts to synthesise such elements have failed so far. An attempt to make element 119 has been ongoing since 2018 at the Riken research institute in Japan. The Joint Institute for Nuclear Research in Russia also plans to make its own attempts at synthesising the first few period 8 elements.

If the eighth period follows the pattern set by the earlier periods, then it would contain fifty elements, filling the 8s, 5g, 6f, 7d, and finally 8p subshells in that order. But there is present discussion regarding whether this would truly be the case, as calculations predict that by this point relativistic effects should result in significant deviations from the Madelung rule. Various different models have been suggested. All agree that the eighth period should begin like the previous ones with two 8s elements, and that there should then follow a new series of g-block elements filling up the 5g orbitals, but the precise configurations calculated for these 5g elements vary widely between sources. Beyond this 5g series, calculations do not agree on what exactly should follow. Filling of the 5g, 6f, 7d, and 8p shells is indeed expected to occur in approximately that order, but they are likely to be intermingled with each other and with the 9s and 9p subshells, so that it is not clear which elements should go in which groups anymore. Eric Scerri has raised the question of whether an extended periodic table should take into account the failure of the Madelung rule in this region, or if such exceptions should be ignored. The shell structure may also be fairly formal at this point: already the electron distribution in an oganesson atom is expected to be rather uniform, with no discernible shell structure.

Nuclear stability will likely prove a decisive factor constraining the number of possible elements. It depends on the balance between the electric repulsion between protons and the strong force binding protons and neutrons together. Protons and neutrons are arranged in shells, just like electrons, and so a closed shell can significantly increase stability: the known superheavy nuclei exist because of such a shell closure. They are probably close to a predicted island of stability, where superheavy nuclides should have significantly longer half-lives: predictions range from minutes or days, to millions or billions of years. However, as the number of protons increases beyond about 126, this stabilising effect should vanish as a closed shell is passed. It is not clear if any further-out shell closures exist, due to an expected smearing out of distinct nuclear shells (as is already expected for the electron shells at oganesson). Furthermore, even if later shell closures exist, it is not clear if they would allow such heavy elements to exist. As such, it may be that the periodic table practically ends around element 120, as elements become too short-lived to observe; the era of discovering new elements would thus be close to its end.

Alternatively, quark matter may become stable at high mass numbers, in which the nucleus is composed of freely flowing up and down quarks instead of binding them into protons and neutrons; this would create a continent of stability instead of an island. Other effects may come into play: for example, in very heavy elements the 1s electrons are likely to spend a significant amount of time so close to the nucleus that they are actually inside it, which would make them vulnerable to electron capture.

Even if eighth-row elements can exist, producing them is likely to be difficult, and it should become even more difficult as atomic number rises. Although the 8s elements are expected to be reachable with present means, the first few 5g elements are expected to require new technology, if they can be produced at all. Experimentally characterising these elements chemically would also pose a great challenge.

Alternative periodic tables

Otto Theodor Benfey's spiral periodic table (1964)

The periodic law may be represented in multiple ways, of which the standard periodic table is only one. Within 100 years of the appearance of Mendeleev's table in 1869, Edward G. Mazurs had collected an estimated 700 different published versions of the periodic table. Many forms retain the rectangular structure, including Charles Janet's left-step periodic table (pictured below), and the modernised form of Mendeleev's original 8-column layout that is still common in Russia. Other periodic table formats have been shaped much more exotically, such as spirals ( Otto Theodor Benfey's pictured to the right), circles and triangles.

Alternative periodic tables are often developed to highlight or emphasize chemical or physical properties of the elements that are not as apparent in traditional periodic tables, with different ones skewed more towards emphasizing chemistry or physics at either end. The standard form, which remains by far the most common, is somewhere in the middle.

The many different forms of the periodic table have prompted the questions of whether there is an optimal or definitive form of the periodic table, and if so, what it might be. There are no current consensus answers to either question. Janet's left-step table is being increasingly discussed as a candidate for being the optimal or most fundamental form; Scerri has written in support of it, as it clarifies helium's nature as an s-block element, increases regularity by having all period lengths repeated, faithfully follows Madelung's rule by making each period correspond to one value of n + ℓ, and regularises atomic number triads and the first-row anomaly trend. While he notes that its placement of helium atop the alkaline earth metals can be seen a disadvantage from a chemical perspective, he counters this by appealing to the first-row anomaly, pointing out that the periodic table "fundamentally reduces to quantum mechanics", and that it is concerned with "abstract elements" and hence atomic properties rather than macroscopic properties.

1. See for example ^ the periodic table poster sold by Sigma-Aldrich.

2. The question of how many natural elements there are is quite complicated and is not fully resolved. In the early Solar System, shorter-lived elements had not yet decayed away, and consequently there were more than 94 naturally occurring elements. ^ Curium (element 96) is the longest-lived element beyond the first 94, and is probably still being brought to Earth via cosmic rays, but it has not been found.[28] Elements up to 99 (einsteinium) have been observed in Przybylski's Star.[29] Elements up to 100 (fermium) probably occurred in the natural nuclear fission reactor at Oklo Mine, Gabon, but they have long since decayed away.[6] Even heavier elements may be produced in the r-process via supernovae or neutron star mergers, but this has not been confirmed. It is not clear how far they would extend past 100 and how long they would last: calculations suggest that nuclides of mass number around 280 to 290 are formed in the r-process, but quickly beta decay to nuclides that suffer spontaneous fission, so that 99.9% of the produced superheavy nuclides would decay within a month.[30] If instead they were sufficiently long-lived, they might similarly be brought to Earth via cosmic rays, but again none have been found.[28]

3. The half-life of ^ plutonium's most stable isotope is just long enough that it should also be a primordial element. A 1971 study claimed to have detected primordial plutonium,[32] but a more recent study from 2012 could not detect it.[33]

4. Once two to four electrons are removed, the d and f orbitals usually become lower in energy than the s ones:^ [51]

1s ≪ 2s < 2p ≪ 3s < 3p ≪ 3d < 4s < 4p ≪ 4d < 5s < 5p ≪ 4f < 5d < 6s < 6p ≪ 5f < 6d < 7s < 7p ≪ ...

and in the limit for extremely highly charged ions, orbitals simply fill in the order of increasingn instead. There is a gradual transition between the limiting situations of highly charged ions (increasing n) and neutral atoms (Madelung's rule).[44] Also, the ordering of the orbitals between each ≪ changes somewhat throughout each period. For example, the ordering in argon and potassium is 3p ≪ 4s < 4p ≪ 3d; by calcium it has become 3p ≪ 4s < 3d < 4p; from scandium to copper it is 3p ≪ 3d < 4s < 4p; and from zinc to krypton it is 3p < 3d ≪ 4s < 4p[50] as the d-orbitals fall into the core at gallium.[52][53]

5. In fact, electron configurations represent a first-order approximation: an atom really exists in a superposition of multiple configurations, and electrons in an atom are indistinguishable.^ [14] The elements in the d- and f-blocks have multiple configurations separated by small energies and can change configuration depending on the chemical environment.[51] In some of the undiscovered g-block elements, it is predicted that mixing of configurations should become so important that the result can no longer be well-described by a single configuration.[55]

6. There are many lower oxides as well: for example, ^ phosphorus in group 15 forms two oxides, P₂O₃ and P₂O₅.[99]

7. The normally "forbidden" intermediate oxidation states may be stabilised by forming ^ dimers, as in [Cl₃Ga-GaCl₃]2− (gallium in the +2 oxidation state) or S₂F₁₀ (sulfur in the +5 oxidation state).[119]

8. All this describes the situation at standard pressure. Under sufficiently high pressure, the band gaps of any solid drop to zero and metallisation occurs. Thus for example at about 170 ^ kbar iodine becomes a metal,[129] and metallic hydrogen should form at pressures of about four million atmospheres.[130]

9. Descriptions of the structures formed by the elements can be found throughout Greenwood and Earnshaw. There are two borderline cases. Arsenic's most stable form conducts electricity like a metal, but the bonding is significantly more localised to the nearest neighbours than it is for the similar structures of antimony and bismuth.^ [133] Carbon as graphite shows metallic conduction parallel to its planes, but is a semiconductor perpendicular to them. Some computations predict copernicium and flerovium to be nonmetallic,[134][135] but the most recent experiments on them suggest that they are metallic.[136][137][138] Astatine is calculated to metallise at standard conditions,[139] so presumably tennessine should as well.[140]

10. See ^ melting points of the elements (data page). The same is probably true of francium, but due to its extreme instability, this has never been experimentally confirmed. Copernicium and flerovium are expected to be liquids,[134][135] similar to mercury, and experimental evidence suggests that they are metals.[136][137][138]

11. See ^ lists of metalloids. For example, a periodic table used by the American Chemical Society includes polonium as a metalloid,[151] but one used by the Royal Society of Chemistry does not,[152] and that included in the Encyclopædia Britannica does not refer to metalloids or semi-metals at all.[153] Classification can change even within a single work. For example, Sherwin and Weston's Chemistry of the Non-Metallic Elements (1966) has a periodic table on p. 7 classifying antimony as a nonmetal, but on p. 115 it is called a metal.[154]

12. See ^ post-transition metal.

13. Demkov and Ostrovsky consider the potential ^ where and are constant parameters; this approaches a Coulomb potential for small . When satisfies the condition , where , the zero-energy solutions to the Schrödinger equation for this potential can be described analytically with Gegenbauer polynomials. As passes through each of these values, a manifold containing all states with that value of arises at zero energy and then becomes bound, recovering the Madelung order. Perturbation-theory considerations show that states with smaller have lower energy, and that the s-orbitals (with ) have their energies approaching the next group.[206][84]

14. Technetium, promethium, astatine, neptunium, and plutonium were eventually discovered to occur in nature as well, albeit in tiny traces. See ^ timeline of chemical element discoveries.

15. A simplistic interpretation of the ^ relativistic Dirac equation runs into problems with electron orbitals at Z > 1/α ≈ 137; this would suggest that neutral atoms cannot exist beyond element 137, and that a periodic table of elements based on electron orbitals therefore breaks down at this point.[229] However, this argument presumes that the atomic nucleus is pointlike. A more accurate calculation must take into account the small, but nonzero, size of the nucleus, which pushes the limit to Z = 173. Moreover, it turns out that the prohibition is not against neutral atoms, but against bare nuclei: atoms with over 173 protons cannot be totally ionised because their 1s shell would be filled by spontaneous electron-positron pair production, but encounter no difficulties if their 1s shell is already filled.[230]

References

1. ^ Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265-91. doi:10.1515/pac-2015-0305.

2. ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.

3. An ^ element zero (i.e. a substance composed purely of neutrons), is included in a few alternate presentations, for example, in the Chemical Galaxy. See Labarca, M. (2016). "An element of atomic number zero?". New Journal of Chemistry. 40 (11): 9002-06. doi:10.1039/C6NJ02076C.

4. Emsley, John (2011). Nature's Building Blocks: An A-Z guide to the elements (New ed.). New York, NY: Oxford University Press. ISBN 978-0-19-960563-7.

5. ^ Silva, Robert J. (2006). "Fermium, Mendelevium, Nobelium and Lawrencium". In Morss, L. R.; Edelstein, N. M.; Fuger, J. (eds.). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht: Springer Science+Business Media. ISBN 978-1-4020-3555-5.

6. Scerri, Eric (18 January 2021). "Provisional Report on Discussions on Group 3 of the Periodic Table" (PDF). Chemistry International. 43 (1): 31-34. doi:10.1515/ci-2021-0115. S2CID 231694898. Archived (PDF) from the original on 13 April 2021.

7. Jensen, William B. (2015). "The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table: an update". Foundations of Chemistry. 17: 23-31. doi:10.1007/s10698-015-9216-1. S2CID 98624395. Archived from the original on 30 January 2021.

8. Chemey, Alexander T.; Albrecht-Schmitt, Thomas E. (2019). "Evolution of the periodic table through the synthesis of new elements". Radiochimica Acta. 107 (9-11): 1-31. doi:10.1515/ract-2018-3082.

9. ^ Pfeiffer, Paul (1920). "Die Befruchtung der Chemie durch die Röntgenstrahlenphysik". Naturwissenschaften (in German). 8 (50): 984-991. Bibcode:1920NW......8..984P. doi:10.1007/BF02448807. S2CID 7071495.

10. ^ Gonick, First; Criddle, Craig (2005). The Cartoon Guide to Chemistry. Collins. pp. 17-65. ISBN 0-06-093677-0.

11. "The constitution of group 3 of the periodic table". IUPAC. 2015. Archived from the original on 5 July 2016.

12. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006-) "Atomic number". doi:10.1351/goldbook.A00499

13. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006-) "Chemical element". doi:10.1351/goldbook.C01022

14. ^ Gopka, V.F.; Yushchenko, A.V.; Yushchenko, V.A.; Panov, I.V.; Kim, Ch. (15 May 2008). "Identification of absorption lines of short half-life actinides in the spectrum of Przybylski's star (HD 101065)". Kinematics and Physics of Celestial Bodies. 24 (2): 89-98. Bibcode:2008KPCB...24...89G. doi:10.3103/S0884591308020049. S2CID 120526363.

15. ^ Marcillac, Pierre de; Noël Coron; Gérard Dambier; Jacques Leblanc; Jean-Pierre Moalic (April 2003). "Experimental detection of α-particles from the radioactive decay of natural bismuth". Nature. 422 (6934): 876-878. Bibcode:2003Natur.422..876D. doi:10.1038/nature01541. PMID 12712201. S2CID 4415582.

16. ^ Hoffman, D. C.; Lawrence, F. O.; Mewherter, J. L.; Rourke, F. M. (1971). "Detection of Plutonium-244 in Nature". . 234 (5325): 132-134. Bibcode:1971Natur.234..132H. doi:10.1038/234132a0. S2CID 4283169.

17. ^ Lachner, J.; et al. (2012). "Attempt to detect primordial ²⁴⁴Pu on Earth". Physical Review C. 85 (1): 015801. Bibcode:2012PhRvC..85a5801L. doi:10.1103/PhysRevC.85.015801.

18. ^ Wallner, A.; Faestermann, T.; Feige, J.; Feldstein, C.; Knie, K.; Korschinek, G.; et al. (2015). "Abundance of live ²⁴⁴Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis". Nature Communications. 6: 5956. arXiv:. Bibcode:2015NatCo...6.5956W. doi:10.1038/ncomms6956. ISSN 2041-1723. PMC . PMID 25601158.

19. ^ Goudsmit, S. A.; Richards, Paul I. (1964). "The Order of Electron Shells in Ionized Atoms" (PDF). Proc. Natl. Acad. Sci. 51 (4): 664-671 (with correction on p 906). Bibcode:1964PNAS...51..664G. doi:10.1073/pnas.51.4.664. PMC . PMID 16591167. Archived (PDF) from the original on 10 October 2017.

# data[].attributes.attachment_link.description
The periodic table, also known as the periodic table of the elements, arranges the chemical elements into rows (" periods") and columns (" groups"). It is an organizing icon of chemistry and is widely used in physics and other sciences.

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Spectroscopic notation provides a way to specify atomic ionization states, atomic orbitals, and molecular orbitals.

Spectroscopists customarily refer to the spectrum arising from a given ionization state of a given element by the element's symbol followed by a Roman numeral. The numeral I is used for spectral lines associated with the neutral element, II for those from the first ionization state, III for those from the second ionization state, and so on. For example, "He I" denotes lines of neutral helium, and "C IV" denotes lines arising from the third ionization state, C ³⁺, of carbon. This notation is used for example to retrieve data from the NIST Atomic Spectrum Database.

Before atomic orbitals were understood, spectroscopists discovered various distinctive series of spectral lines in atomic spectra, which they identified by letters. These letters were later associated with the azimuthal quantum number, ℓ. The letters, "s", "p", "d", and "f", for the first four values of ℓ were chosen to be the first letters of properties of the spectral series observed in alkali metals. Other letters for subsequent values of ℓ were assigned in alphabetical order, omitting the letter "j" because some languages do not distinguish between the letters "i" and "j":

This notation is used to specify electron configurations and to create the term symbol for the electron states in a multi-electron atom. When writing a term symbol, the above scheme for a single electron's orbital quantum number is applied to the total orbital angular momentum associated to an electron state.

Molecular spectroscopic notation

The spectroscopic notation of molecules uses Greek letters to represent the modulus of the orbital angular momentum along the internuclear axis. The quantum number that represents this angular momentum is Λ.

For Σ states, one denotes if there is a reflection in a plane containing the nuclei (symmetric), using the + above. The − is used to indicate that there is not.

For homonuclear diatomic molecules, the index g or u denotes the existence of a center of symmetry (or inversion center) and indicates the symmetry of the vibronic wave function with respect to the point-group inversion operation i. Vibronic states that are symmetric with respect to i are denoted g for gerade (German for "even"), and unsymmetric states are denoted u for ungerade (German for "odd").

For mesons whose constituents are a heavy quark and its own antiquark ( quarkonium) the same notation applies as for atomic states. However, uppercase letters are used.

Furthermore, the first number is (as in nuclear physics) where is the number of nodes in the radial wave function, while in atomic physics is used. Hence, a 1P state in quarkonium corresponds to a 2p state in an atom or positronium.

# data[].attributes.attachment_link.description
Spectroscopic notation provides a way to specify atomic ionization states, atomic orbitals, and molecular orbitals. Spectroscopists customarily refer to the spectrum arising from a given ionization state of a given element by the element's symbol followed by a Roman numeral.

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Orbits with zero angular momentum were considered as oscillating charges in one dimension and so described as "pendulum" orbits, but were not found in nature.[2] In three-dimensions the orbits become spherical without any nodes crossing the nucleus, similar (in the lowest-energy state) to a skipping rope that oscillates in one large circle.

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0 = Lyman series value for ultraviolet wavelength of hydrogen

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0 = Lyman series value for ultraviolet wavelength of hydrogen

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In physics and chemistry, the Lyman series is a hydrogen spectral series of transitions and resulting ultraviolet emission lines of the hydrogen atom as an electron goes from ≥ 2 to = 1 (where n is the principal quantum number), the lowest energy level of the electron. The transitions are named sequentially by Greek letters: from = 2 to n = 1 is called Lyman-alpha, 3 to 1 is Lyman-beta, 4 to 1 is Lyman-gamma, and so on. The series is named after its discoverer, Theodore Lyman. The greater the difference in the principal quantum numbers, the higher the energy of the electromagnetic emission.

The first line in the spectrum of the Lyman series was discovered in 1906 by Harvard physicist Theodore Lyman, who was studying the ultraviolet spectrum of electrically excited hydrogen gas. The rest of the lines of the spectrum (all in the ultraviolet) were discovered by Lyman from 1906-1914. The spectrum of radiation emitted by hydrogen is non-continuous or discrete. Here is an illustration of the first series of hydrogen emission lines:

Historically, explaining the nature of the hydrogen spectrum was a considerable problem in physics. Nobody could predict the wavelengths of the hydrogen lines until 1885 when the Balmer formula gave an empirical formula for the visible hydrogen spectrum. Within five years Johannes Rydberg came up with an empirical formula that solved the problem, presented first in 1888 and final form in 1890. Rydberg managed to find a formula to match the known Balmer series emission lines, and also predicted those not yet discovered. Different versions of the Rydberg formula with different simple numbers were found to generate different series of lines.

On December 1, 2011, it was announced that Voyager 1 detected the first Lyman-alpha radiation originating from the Milky Way galaxy. Lyman-alpha radiation had previously been detected from other galaxies, but due to interference from the Sun, the radiation from the Milky Way was not detectable.

The version of the Rydberg formula that generated the Lyman series was:

where n is a natural number greater than or equal to 2 (i.e., n = 2, 3, 4, ...).

Therefore, the lines seen in the image above are the wavelengths corresponding to n = 2 on the right, to n = ∞ on the left. There are infinitely many spectral lines, but they become very dense as they approach n = ∞ (the Lyman limit), so only some of the first lines and the last one appear.

The wavelengths in the Lyman series are all ultraviolet:

In 1914, when Niels Bohr produced his Bohr model theory, the reason why hydrogen spectral lines fit Rydberg's formula was explained. Bohr found that the electron bound to the hydrogen atom must have quantized energy levels described by the following formula,

According to Bohr's third assumption, whenever an electron falls from an initial energy level E i to a final energy level E f, the atom must emit radiation with a wavelength of

There is also a more comfortable notation when dealing with energy in units of electronvolts and wavelengths in units of angstroms,

Å.

Replacing the energy in the above formula with the expression for the energy in the hydrogen atom where the initial energy corresponds to energy level n and the final energy corresponds to energy level m,

Where R H is the same Rydberg constant for hydrogen from Rydberg's long known formula. This also means that the inverse of the Rydberg constant is equal to the Lyman limit.

For the connection between Bohr, Rydberg, and Lyman, one must replace m with 1 to obtain

which is Rydberg's formula for the Lyman series. Therefore, each wavelength of the emission lines corresponds to an electron dropping from a certain energy level (greater than 1) to the first energy level.

# data[].attributes.attachment_link.description
In physics and chemistry, the Lyman series is a hydrogen spectral series of transitions and resulting ultraviolet emission lines of the hydrogen atom as an electron goes from ≥ 2 to = 1 (where n is the principal quantum number), the lowest energy level of the electron.

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The azimuthal quantum number is a quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital. The azimuthal quantum number is the second of a set of quantum numbers that describe the unique quantum state of an electron (the others being the principal quantum number, the magnetic quantum number, and the spin quantum number). It is also known as the orbital angular momentum quantum number, orbital quantum number or second quantum number, and is symbolized as ℓ (pronounced ell).

Connected with the energy states of the atom's electrons are four quantum numbers: n, ℓ, m ℓ, and m s. These specify the complete, unique quantum state of a single electron in an atom, and make up its wavefunction or orbital. When solving to obtain the wave function, the Schrödinger equation reduces to three equations that lead to the first three quantum numbers. Therefore, the equations for the first three quantum numbers are all interrelated. The azimuthal quantum number arose in the solution of the polar part of the wave equation as shown below[where? ], reliant on the spherical coordinate system, which generally works best with models having some glimpse of spherical symmetry.

An atomic electron's angular momentum, L, is related to its quantum number ℓ by the following equation:

where ħ is the reduced Planck's constant, L ² is the orbital angular momentum operator and is the wavefunction of the electron. The quantum number ℓ is always a non-negative integer: 0, 1, 2, 3, etc. L has no real meaning except in its use as the angular momentum operator. When referring to angular momentum, it is better to simply use the quantum number ℓ.

Atomic orbitals have distinctive shapes denoted by letters. In the illustration, the letters s, p, and d (a convention originating in spectroscopy) describe the shape of the atomic orbital.

Their wavefunctions take the form of spherical harmonics, and so are described by Legendre polynomials. The various orbitals relating to different values of ℓ are sometimes called sub-shells, and are referred to by lowercase Latin letters (chosen for historical reasons), as follows:

Each of the different angular momentum states can take 2(2 ℓ + 1) electrons. This is because the third quantum number m ℓ (which can be thought of loosely as the quantized projection of the angular momentum vector on the z-axis) runs from − ℓ to ℓ in integer units, and so there are 2 ℓ + 1 possible states. Each distinct n,  ℓ,  m ℓ orbital can be occupied by two electrons with opposing spins (given by the quantum number m s = ±), giving 2(2 ℓ + 1) electrons overall. Orbitals with higher ℓ than given in the table are perfectly permissible, but these values cover all atoms so far discovered.

For a given value of the principal quantum number n, the possible values of ℓ range from 0 to n − 1; therefore, the n = 1 shell only possesses an s subshell and can only take 2 electrons, the n = 2 shell possesses an s and a p subshell and can take 8 electrons overall, the n = 3 shell possesses s, p, and d subshells and has a maximum of 18 electrons, and so on.

A simplistic one-electron model results in energy levels depending on the principal number alone. In more complex atoms these energy levels split for all n > 1, placing states of higher ℓ above states of lower ℓ. For example, the energy of 2p is higher than of 2s, 3d occurs higher than 3p, which in turn is above 3s, etc. This effect eventually forms the block structure of the periodic table. No known atom possesses an electron having ℓ higher than three ( f) in its ground state.

The angular momentum quantum number, ℓ, governs[how? ] the number of planar nodes going through the nucleus. A planar node can be described in an electromagnetic wave as the midpoint between crest and trough, which has zero magnitudes. In an s orbital, no nodes go through the nucleus, therefore the corresponding azimuthal quantum number ℓ takes the value of 0. In a p orbital, one node traverses the nucleus and therefore ℓ has the value of 1. has the value .

Depending on the value of n, there is an angular momentum quantum number ℓ and the following series. The wavelengths listed are for a hydrogen atom:

, Lyman series (ultraviolet)

, Balmer series (visible)

, Ritz-Paschen series (near infrared)

, Brackett series (short-wavelength infrared)

, Pfund series (mid-wavelength infrared).

Given a quantized total angular momentum which is the sum of two individual quantized angular momenta and ,

the quantum number associated with its magnitude can range from to in integer steps where and are quantum numbers corresponding to the magnitudes of the individual angular momenta.

Total angular momentum of an electron in the atom

Due to the spin-orbit interaction in the atom, the orbital angular momentum no longer commutes with the Hamiltonian, nor does the spin. These therefore change over time. However the total angular momentum J does commute with the one-electron Hamiltonian and so is constant. J is defined through

L being the orbital angular momentum and S the spin. The total angular momentum satisfies the same commutation relations as orbital angular momentum, namely

from which follows

The quantum numbers describing the system, which are constant over time, are now j and m j, defined through the action of J on the wavefunction

So that j is related to the norm of the total angular momentum and m j to its projection along a specified axis. The j number has a particular importance for relativistic quantum chemistry, often featuring in subscript in electron configuration of superheavy elements.

As with any angular momentum in quantum mechanics, the projection of J along other axes cannot be co-defined with J z, because they do not commute.

Relation between new and old quantum numbers

j and m j, together with the parity of the quantum state, replace the three quantum numbers ℓ, m ℓ and m s (the projection of the spin along the specified axis). The former quantum numbers can be related to the latter.

The azimuthal quantum number was carried over from the Bohr model of the atom, and was posited by Arnold Sommerfeld. The Bohr model was derived from spectroscopic analysis of the atom in combination with the Rutherford atomic model. The lowest quantum level was found to have an angular momentum of zero. Orbits with zero angular momentum were considered as oscillating charges in one dimension and so described as "pendulum" orbits, but were not found in nature. In three-dimensions the orbits become spherical without any nodes crossing the nucleus, similar (in the lowest-energy state) to a skipping rope that oscillates in one large circle.

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The azimuthal quantum number is a quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital. The azimuthal quantum number is the second of a set of quantum numbers that describe the unique quantum state of an electron (the others being the principal quantum number, the magnetic quantum number, and the spin quantum number).

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The shapes of the first five atomic orbitals are: 1s, 2s, 2pψ(ψ(x, 2py, and 2pz. The two colors show the phase or sign of the wave function in each region. Each picture is domain coloring of a x, x, y, z)² functions that show y, z) function which depends on the coordinates of one electron. To see the elongated shape of probability density more directly, see pictures of d-orbitals below.

In atomic theory and quantum mechanics, an atomic orbital () is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The term atomic orbital may also refer to the physical region or space where the electron can be calculated to be present, as predicted by the particular mathematical form of the orbital.

Each orbital in an atom is characterized by a set of values of the three m quantum numbers n, ℓ, and angular momentum, and an angular momentum l, which respectively correspond to the electron's energy, its vector component ( magnetic quantum number). As an alternative to the magnetic quantum number, the orbitals are often labeled by the associated harmonic polynomials (e.g., xy, spin x ² − y . The simple names ²). Each such orbital can be occupied by a maximum of two electrons, each with its own projection of s orbital, p orbital, d orbital, and ℓ = 0, 1, 2, and f orbital refer to orbitals with angular momentum quantum number 3 respectively. These names, together with the value of n, are used to describe the electron configurations of atoms. They are derived from the description by early spectroscopists of certain series of alkali metal spectroscopic lines as sharp, principal, diffuse, and fundamental. Orbitals for ℓ > 3 continue alphabetically (g, h, i, k, ...),[3] omitting j[4][5] because some languages do not distinguish between the letters "i" and "j".[6]

Atomic orbitals are the basic building blocks of the atomic orbital model (or electron cloud or wave mechanics model), a modern framework for visualizing the submicroscopic behavior of electrons in matter. In this model the electron cloud of an atom may be seen as being built up (in approximation) in an electron configuration that is a product of simpler hydrogen-like atomic orbitals. The repeating periodicity of blocks of 2, 6, 10, and 14 elements within sections of the periodic table arises naturally from the total number of electrons that occupy a complete set of s, p, d, and f orbitals, respectively, though for higher values of quantum number n, particularly when the atom bears a positive charge, the energies of certain sub-shells become very similar and so the order in which they are said to be populated by electrons (e.g., Cr = [Ar]4s ¹3d ⁵ and Cr ²⁺ = [Ar]3d ⁴) can be rationalized only somewhat arbitrarily.

Atomic orbitals of the electron in a hydrogen atom at different energy levels. The probability of finding the electron is given by the color, as shown in the key at upper right.

With the development of quantum mechanics and experimental findings (such as the two slit diffraction of electrons), it was found that the electrons orbiting a nucleus could not be fully described as particles, but needed to be explained by wave-particle duality. In this sense, electrons have the following properties:

Wave-like properties:

1. Electrons do not orbit a nucleus in the manner of a planet orbiting the Sun, but instead exist as standing waves. Thus the lowest possible energy an electron can take is similar to the fundamental frequency of a wave on a string. Higher energy states are similar to harmonics of that fundamental frequency.

2. The electrons are never in a single point location, though the probability of interacting with the electron at a single point can be found from the electron's wave function. The electron's charge acts like it is smeared out in space in a continuous distribution, proportional at any point to the squared magnitude of the electron's wave function.

Particle-like properties:

1. The number of electrons orbiting a nucleus can be only an integer.

2. Electrons jump between orbitals like particles. For example, if one photon strikes the electrons, only one electron changes state as a result.

3. Electrons retain particle-like properties such as: each wave state has the same electric charge as its electron particle. Each wave state has a single discrete spin (spin up or spin down) depending on its superposition.

Thus, electrons cannot be described simply as solid particles. An analogy might be that of a large and often oddly shaped "atmosphere" (the electron), distributed around a relatively tiny planet (the nucleus). Atomic orbitals exactly describe the shape of this "atmosphere" only when one electron is present. When more electrons are added, the additional electrons tend to more evenly fill in a volume of space around the nucleus so that the resulting collection ("electron cloud") tends toward a generally spherical zone of probability describing the electron's location, because of the uncertainty principle.

Atomic orbitals may be defined more precisely in formal quantum mechanical language. They are approximate solutions to the Schrödinger equation for the electrons bound to the atom by the electric field of the atom's nucleus. Specifically, in quantum mechanics, the state of an atom, i.e., an eigenstate of the atomic Hamiltonian, is approximated by an expansion (see configuration interaction expansion and basis set) into linear combinations of anti-symmetrized products ( Slater determinants) of one-electron functions. The spatial components of these one-electron functions are called atomic orbitals. (When one considers also their spin component, one speaks of atomic spin orbitals.) A state is actually a function of the coordinates of all the electrons, so that their motion is correlated, but this is often approximated by this independent-particle model of products of single electron wave functions. (The London dispersion force, for example, depends on the correlations of the motion of the electrons.)

In atomic physics, the atomic spectral lines correspond to transitions ( quantum leaps) between quantum states of an atom. These states are labeled by a set of quantum numbers summarized in the term symbol and usually associated with particular electron configurations, i.e., by occupation schemes of atomic orbitals (for example, 1s ² 2s ² 2p ⁶ for the ground state of neon-term symbol: ¹S ₀).

This notation means that the corresponding Slater determinants have a clear higher weight in the configuration interaction expansion. The atomic orbital concept is therefore a key concept for visualizing the excitation process associated with a given transition. For example, one can say for a given transition that it corresponds to the excitation of an electron from an occupied orbital to a given unoccupied orbital. Nevertheless, one has to keep in mind that electrons are fermions ruled by the Pauli exclusion principle and cannot be distinguished from each other. Moreover, it sometimes happens that the configuration interaction expansion converges very slowly and that one cannot speak about simple one-determinant wave function at all. This is the case when electron correlation is large.

Fundamentally, an atomic orbital is a one-electron wave function, even though many electrons are not in one-electron atoms, and so the one-electron view is an approximation. When thinking about orbitals, we are often given an orbital visualization heavily influenced by the Hartree-Fock approximation, which is one way to reduce the complexities of molecular orbital theory.

3D views of some hydrogen-like atomic orbitals showing probability density and phase (g orbitals and higher are not shown)

Atomic orbitals can be the hydrogen-like "orbitals" which are exact solutions to the Schrödinger equation for a hydrogen-like "atom" (i.e., atom with one electron). Alternatively, atomic orbitals refer to functions that depend on the coordinates of one electron (i.e., orbitals) but are used as starting points for approximating wave functions that depend on the simultaneous coordinates of all the electrons in an atom or molecule. The coordinate systems chosen for orbitals are usually spherical coordinates in atoms and Cartesian in polyatomic molecules. The advantage of spherical coordinates here is that an orbital wave function is a product of three factors each dependent on a single coordinate: . The angular factors of atomic orbitals generate s, p, d, etc. functions as real combinations of spherical harmonics (where ℓ and m are quantum numbers). There are typically three mathematical forms for the radial functions which can be chosen as a starting point for the calculation of the properties of atoms and molecules with many electrons:

1. The hydrogen-like orbitals are derived from the exact solutions of the Schrödinger equation for one electron and a nucleus, for a hydrogen-like atom. The part of the function that depends on distance r from the nucleus has radial nodes and decays as .

2. The Slater-type orbital (STO) is a form without radial nodes but decays from the nucleus as does a hydrogen-like orbital.

3. The form of the Gaussian type orbital (Gaussians) has no radial nodes and decays as .

Although hydrogen-like orbitals are still used as pedagogical tools, the advent of computers has made STOs preferable for atoms and diatomic molecules since combinations of STOs can replace the nodes in hydrogen-like orbitals. Gaussians are typically used in molecules with three or more atoms. Although not as accurate by themselves as STOs, combinations of many Gaussians can attain the accuracy of hydrogen-like orbitals.

The term "orbital" was coined by Robert S. Mulliken in 1932 as short for one-electron orbital wave function. Niels Bohr explained around 1913 that electrons might revolve around a compact nucleus with definite angular momentum. Bohr's model was an improvement on the 1911 explanations of Ernest Rutherford, that of the electron moving around a nucleus. Japanese physicist Hantaro Nagaoka published an orbit-based hypothesis for electron behavior as early as 1904. These theories were each built upon new observations starting with simple understanding and becoming more correct and complex. Explaining the behavior of these electron "orbits" was one of the driving forces behind the development of quantum mechanics.

With J. J. Thomson's discovery of the electron in 1897, it became clear that atoms were not the smallest building blocks of nature, but were rather composite particles. The newly discovered structure within atoms tempted many to imagine how the atom's constituent parts might interact with each other. Thomson theorized that multiple electrons revolve in orbit-like rings within a positively charged jelly-like substance, and between the electron's discovery and 1909, this " plum pudding model" was the most widely accepted explanation of atomic structure.

Shortly after Thomson's discovery, Hantaro Nagaoka predicted a different model for electronic structure. Unlike the plum pudding model, the positive charge in Nagaoka's "Saturnian Model" was concentrated into a central core, pulling the electrons into circular orbits reminiscent of Saturn's rings. Few people took notice of Nagaoka's work at the time, and Nagaoka himself recognized a fundamental defect in the theory even at its conception, namely that a classical charged object cannot sustain orbital motion because it is accelerating and therefore loses energy due to electromagnetic radiation. Nevertheless, the Saturnian model turned out to have more in common with modern theory than any of its contemporaries.

In 1909, Ernest Rutherford discovered that the bulk of the atomic mass was tightly condensed into a nucleus, which was also found to be positively charged. It became clear from his analysis in 1911 that the plum pudding model could not explain atomic structure. In 1913, Rutherford's post-doctoral student, Niels Bohr, proposed a new model of the atom, wherein electrons orbited the nucleus with classical periods, but were permitted to have only discrete values of angular momentum, quantized in units ħ. This constraint automatically allowed only certain electron energies. The Bohr model of the atom fixed the problem of energy loss from radiation from a ground state (by declaring that there was no state below this), and more importantly explained the origin of spectral lines.

The Rutherford-Bohr model of the hydrogen atom.

After Bohr's use of Einstein's explanation of the photoelectric effect to relate energy levels in atoms with the wavelength of emitted light, the connection between the structure of electrons in atoms and the emission and absorption spectra of atoms became an increasingly useful tool in the understanding of electrons in atoms. The most prominent feature of emission and absorption spectra (known experimentally since the middle of the 19th century), was that these atomic spectra contained discrete lines. The significance of the Bohr model was that it related the lines in emission and absorption spectra to the energy differences between the orbits that electrons could take around an atom. This was, however, not achieved by Bohr through giving the electrons some kind of wave-like properties, since the idea that electrons could behave as matter waves was not suggested until eleven years later. Still, the Bohr model's use of quantized angular momenta and therefore quantized energy levels was a significant step toward the understanding of electrons in atoms, and also a significant step towards the development of quantum mechanics in suggesting that quantized restraints must account for all discontinuous energy levels and spectra in atoms.

With de Broglie's suggestion of the existence of electron matter waves in 1924, and for a short time before the full 1926 Schrödinger equation treatment of hydrogen-like atoms, a Bohr electron "wavelength" could be seen to be a function of its momentum; so a Bohr orbiting electron was seen to orbit in a circle at a multiple of its half-wavelength. The Bohr model for a short time could be seen as a classical model with an additional constraint provided by the 'wavelength' argument. However, this period was immediately superseded by the full three-dimensional wave mechanics of 1926. In our current understanding of physics, the Bohr model is called a semi-classical model because of its quantization of angular momentum, not primarily because of its relationship with electron wavelength, which appeared in hindsight a dozen years after the Bohr model was proposed.

The Bohr model was able to explain the emission and absorption spectra of hydrogen. The energies of electrons in the n = 1, 2, 3, etc. states in the Bohr model match those of current physics. However, this did not explain similarities between different atoms, as expressed by the periodic table, such as the fact that helium (two electrons), neon (10 electrons), and argon (18 electrons) exhibit similar chemical inertness. Modern quantum mechanics explains this in terms of electron shells and subshells which can each hold a number of electrons determined by the Pauli exclusion principle. Thus the n = 1 state can hold one or two electrons, while the n = 2 state can hold up to eight electrons in 2s and 2p subshells. In helium, all n = 1 states are fully occupied; the same is true for n = 1 and n = 2 in neon. In argon, the 3s and 3p subshells are similarly fully occupied by eight electrons; quantum mechanics also allows a 3d subshell but this is at higher energy than the 3s and 3p in argon (contrary to the situation for hydrogen) and remains empty.

Immediately after Heisenberg discovered his uncertainty principle, Bohr noted that the existence of any sort of wave packet implies uncertainty in the wave frequency and wavelength, since a spread of frequencies is needed to create the packet itself. In quantum mechanics, where all particle momenta are associated with waves, it is the formation of such a wave packet which localizes the wave, and thus the particle, in space. In states where a quantum mechanical particle is bound, it must be localized as a wave packet, and the existence of the packet and its minimum size implies a spread and minimal value in particle wavelength, and thus also momentum and energy. In quantum mechanics, as a particle is localized to a smaller region in space, the associated compressed wave packet requires a larger and larger range of momenta, and thus larger kinetic energy. Thus the binding energy to contain or trap a particle in a smaller region of space increases without bound as the region of space grows smaller. Particles cannot be restricted to a geometric point in space, since this would require infinite particle momentum.

In chemistry, Erwin Schrödinger, Linus Pauling, Mulliken and others noted that the consequence of Heisenberg's relation was that the electron, as a wave packet, could not be considered to have an exact location in its orbital. Max Born suggested that the electron's position needed to be described by a probability distribution which was connected with finding the electron at some point in the wave-function which described its associated wave packet. The new quantum mechanics did not give exact results, but only the probabilities for the occurrence of a variety of possible such results. Heisenberg held that the path of a moving particle has no meaning if we cannot observe it, as we cannot with electrons in an atom.

In the quantum picture of Heisenberg, Schrödinger and others, the Bohr atom number n for each orbital became known as an n-sphere[citation needed ] in a three-dimensional atom and was pictured as the most probable energy of the probability cloud of the electron's wave packet which surrounded the atom.

Orbitals have been given names, which are usually given in the form:

where X is the energy level corresponding to the principal quantum number n; type is a lower-case letter denoting the shape or subshell of the orbital, corresponding to the angular momentum quantum number ℓ.

For example, the orbital 1s (pronounced as the individual numbers and letters: "'one' 'ess'") is the lowest energy level ( n = 1) and has an angular quantum number of ℓ = 0, denoted as s. Orbitals with ℓ = 1, 2 and 3 are denoted as p, d and f respectively.

The set of orbitals for a given n and ℓ is called a subshell, denoted

.

The superscript y shows the number of electrons in the subshell. For example, the notation 2p ⁴ indicates that the 2p subshell of an atom contains 4 electrons. This subshell has 3 orbitals, each with n = 2 and ℓ = 1.

There is also another, less common system still used in X-ray science known as X-ray notation, which is a continuation of the notations used before orbital theory was well understood. In this system, the principal quantum number is given a letter associated with it. For n = 1, 2, 3, 4, 5, ..., the letters associated with those numbers are K, L, M, N, O, ... respectively.

The simplest atomic orbitals are those that are calculated for systems with a single electron, such as the hydrogen atom. An atom of any other element ionized down to a single electron is very similar to hydrogen, and the orbitals take the same form. In the Schrödinger equation for this system of one negative and one positive particle, the atomic orbitals are the eigenstates of the Hamiltonian operator for the energy. They can be obtained analytically, meaning that the resulting orbitals are products of a polynomial series, and exponential and trigonometric functions. (see hydrogen atom).

For atoms with two or more electrons, the governing equations can be solved only with the use of methods of iterative approximation. Orbitals of multi-electron atoms are qualitatively similar to those of hydrogen, and in the simplest models, they are taken to have the same form. For more rigorous and precise analysis, numerical approximations must be used.

A given (hydrogen-like) atomic orbital is identified by unique values of three quantum numbers: , , and . The rules restricting the values of the quantum numbers, and their energies (see below), explain the electron configuration of the atoms and the periodic table.

The stationary states ( quantum states) of the hydrogen-like atoms are its atomic orbitals.[clarification needed ] However, in general, an electron's behavior is not fully described by a single orbital. Electron states are best represented by time-depending "mixtures" ( linear combinations) of multiple orbitals. See Linear combination of atomic orbitals molecular orbital method.

The quantum number n first appeared in the Bohr model where it determines the radius of each circular electron orbit. In modern quantum mechanics however, n determines the mean distance of the electron from the nucleus; all electrons with the same value of n lie at the same average distance. For this reason, orbitals with the same value of n are said to comprise a " shell". Orbitals with the same value of n and also the same value of ℓ are even more closely related, and are said to comprise a " subshell".

Because of the quantum mechanical nature of the electrons around a nucleus, atomic orbitals can be uniquely defined by a set of integers known as quantum numbers. These quantum numbers occur only in certain combinations of values, and their physical interpretation changes depending on whether real or complex versions of the atomic orbitals are employed.

Energetic levels and sublevels of polyelectronic atoms.

In physics, the most common orbital descriptions are based on the solutions to the hydrogen atom, where orbitals are given by the product between a radial function and a pure spherical harmonic. The quantum numbers, together with the rules governing their possible values, are as follows:

The principal quantum number n describes the energy of the electron and is always a positive integer. In fact, it can be any positive integer, but for reasons discussed below, large numbers are seldom encountered. Each atom has, in general, many orbitals associated with each value of n; these orbitals together are sometimes called electron shells.

The azimuthal quantum number ℓ describes the orbital angular momentum of each electron and is a non-negative integer. Within a shell where n is some integer ℓ ranges across all (integer) values satisfying the relation n ₀, . For instance, the n = 1 shell has only orbitals with , and the n = 2 shell has only orbitals with , and ℓ are sometimes collectively called a . The set of orbitals associated with a particular value of subshell.

The magnetic quantum number, , describes the magnetic moment of an electron in an arbitrary direction, and is also always an integer. Within a subshell where is some integer , ranges thus: .

The above results may be summarized in the following table. Each cell represents a subshell, and lists the values of available in that subshell. Empty cells represent subshells that do not exist.

ℓ = 0 (s)

ℓ = 1 (p)

ℓ = 2 (d)

ℓ = 3 (f)

ℓ = 4 (g)

...

n = 1

...

...

...

...

...

...

...

...

Subshells are usually identified by their - and -values. is represented by its numerical value, but is represented by a letter as follows: 0 is represented by 's', 1 by 'p', 2 by 'd', 3 by 'f', and 4 by 'g'. For instance, one may speak of the subshell with and as a '2s subshell'.

Each electron also has a spin quantum number, s, which describes the spin of each electron (spin up or spin down). The number s can be + or −.

The Pauli exclusion principle states that no two electrons in an atom can have the same values of all four quantum numbers. If there are two electrons in an orbital with given values for three quantum numbers, (n, ℓ, m), these two electrons must differ in their spin.

The above conventions imply a preferred axis (for example, the z direction in Cartesian coordinates), and they also imply a preferred direction along this preferred axis. Otherwise there would be no sense in distinguishing m = +1 from m = −1. As such, the model is most useful when applied to physical systems that share these symmetries. The Stern-Gerlach experiment -where an atom is exposed to a magnetic field-provides one such example.

Animation of continuously varying superpositions between the and the orbitals. Note that this animation does not use the Condon-Shortley phase convention.

In addition to the complex orbitals described above, it is common, especially in the chemistry literature, to use real atomic orbitals. These real orbitals arise from simple linear combinations of complex orbitals. Using the Condon-Shortley phase convention, real orbitals are related to complex orbitals in the same way that the real spherical harmonics are related to complex spherical harmonics. Letting denote a complex orbital with quantum numbers , , and , the real orbitals may be defined by[21]

If , with the radial part of the orbital, this definition is equivalent to where is the real spherical harmonic related to either the real or imaginary part of the complex spherical harmonic .

Real spherical harmonics are physically relevant when an atom is embedded in a crystalline solid, in which case there are multiple preferred symmetry axes but no single preferred direction.[citation needed ] Real atomic orbitals are also more frequently encountered in introductory chemistry textbooks and shown in common orbital visualizations.[22] In real hydrogen-like orbitals, quantum numbers and have the same interpretation and significance as their complex counterparts, but is no longer a good quantum number (but its absolute value is).

Some real orbitals are given specific names beyond the simple designation. Orbitals with quantum number equal to are called orbitals. With this one can already assign names to complex orbitals such as ; the first symbol is the quantum number, the second character is the symbol for that particular quantum number and the subscript is the quantum number.

As an example of how the full orbital names are generated for real orbitals, one may calculate . From the table of spherical harmonics, with . Then

Likewise . As a more complicated example:

In all these cases we generate a Cartesian label for the orbital by examining, and abbreviating, the polynomial in , , and appearing in the numerator. We ignore any terms in the polynomial except for the term with the highest exponent in . We then use the abbreviated polynomial as a subscript label for the atomic state, using the same nomenclature as above to indicate the and quantum numbers.

The expression above all use the Condon-Shortley phase convention which is favored by quantum physicists.[23][24] Other conventions exist for the phase of the spherical harmonics.[25][26] Under these different conventions the and orbitals may appear, for example, as the sum and difference of and , contrary to what is shown above.

Below is a list of these Cartesian polynomial names for the atomic orbitals.[27][28] Note that there does not seem to be reference in the literature as to how to abbreviate the long Cartesian spherical harmonic polynomials for so there does not seem be consensus on the naming of orbitals or higher according to this nomenclature.

m = −3

m = −2

m = −1

m = 0

m = +1

m = +2

m = +3

Transparent cloud view of a computed 6s (n = 6, n > 1. Only s orbitals invariably have a center anti-node; the other types never do.ℓ = 0, m = 0) hydrogen orbital. The s orbitals, though spherically symmetric, have radially placed wave-nodes for

Simple pictures showing orbital shapes are intended to describe the angular forms of regions in space where the electrons occupying the orbital are likely to be found. The diagrams cannot show the entire region where an electron can be found, since according to quantum mechanics there is a non-zero probability of finding the electron (almost) anywhere in space. Instead the diagrams are approximate representations of boundary or contour surfaces where the probability density has a constant value, chosen so that there is a certain probability (for example 90%) of finding the electron within the contour. Although as the square of an absolute value is everywhere non-negative, the sign of the wave function is often indicated in each subregion of the orbital picture.

Sometimes the ψ function is graphed to show its phases, rather than which shows probability density but has no phase (which is lost when taking absolute value, since is a complex number). orbital graphs tend to have less spherical, thinner lobes than graphs, but have the same number of lobes in the same places, and otherwise are recognizable. This article, to show wave function phase, shows mostly graphs.

The lobes can be seen as − standing wave interference patterns between the two counter rotating, ring resonant traveling wave m and m modes; the projection of the orbital onto the xy plane has a resonant m wavelength around the circumference. Although rarely shown, the traveling wave solutions can be seen as rotating banded tori; the bands represent phase information. For each m there are two standing wave solutions and . If z-axis symmetric. If m = 0, the orbital is vertical, counter rotating information is unknown, and the orbital is n, the smaller ℓ is, the more radial nodes there are. For any given ℓ = 0 there are no counter rotating modes. There are only radial modes and the shape is spherically symmetric. For any given ℓ, the smaller n is, the fewer radial nodes there are (zero for whichever n first has that ℓ orbital). Loosely speaking, n is energy, ℓ is analogous to eccentricity, and m is orientation. In the classical case, a ring resonant traveling wave, for example in a circular transmission line, unless actively forced, spontaneously decays into a ring resonant standing wave because reflections build up over time at even the smallest imperfection or discontinuity.

In general, n determines size and energy of the orbital for a given nucleus; as n increases, the size of the orbital increases. The higher nuclear charge Z of heavier elements causes their orbitals to contract by comparison to lighter ones, so that the size of the atom remains very roughly constant, even as the number of electrons increases.

Experimentally imaged 1s and 2p core-electron orbitals of Sr, including the effects of atomic thermal vibration and excitation broadening, retrieved from energy dispersive x-ray spectroscopy (EDX) in scanning transmission electron microscopy (STEM).[29]

Also in general terms, ℓ determines an orbital's shape, and its orientation. However, since some orbitals are described by equations in complex numbers, the shape sometimes depends on also. Together, the whole set of orbitals for a given ℓ and n fill space as symmetrically as possible, though with increasingly complex sets of lobes and nodes.

The single s orbitals ( ) are shaped like spheres. For n = 1 it is roughly a solid ball (densest at center and fades outward exponentially), but for n ≥ 2, each single s orbital is made of spherically symmetric surfaces which are nested shells (i.e., the "wave-structure" is radial, following a sinusoidal radial component as well). See illustration of a cross-section of these nested shells, at right. The s orbitals for all n numbers are the only orbitals with an anti-node (a region of high wave function density) at the center of the nucleus. All other orbitals (p, d, f, etc.) have angular momentum, and thus avoid the nucleus (having a wave node at the nucleus). Recently, there has been an effort to experimentally image the 1s and 2p orbitals in a SrTiO ₃ crystal using scanning transmission electron microscopy with energy dispersive x-ray spectroscopy.[29] Because the imaging was conducted using an electron beam, Coulombic beam-orbital interaction that is often termed as the impact parameter effect is included in the outcome (see the figure at right).

The shapes of p, d and f orbitals are described verbally here and shown graphically in the Orbitals table below. The three p orbitals for n = 2 have the form of two ellipsoids with a point of tangency at the nucleus (the two-lobed shape is sometimes referred to as a " dumbbell"-there are two lobes pointing in opposite directions from each other). The three p orbitals in each shell are oriented at right angles to each other, as determined by their respective linear combination of values of . The overall result is a lobe pointing along each direction of the primary axes.

Four of the five d orbitals for n = 3 look similar, each with four pear-shaped lobes, each lobe tangent at right angles to two others, and the centers of all four lying in one plane. Three of these planes are the xy-, xz-, and yz-planes-the lobes are between the pairs of primary axes-and the fourth has the center along the x and y axes themselves. The fifth and final d orbital consists of three regions of high probability density: a torus in between two pear-shaped regions placed symmetrically on its z axis. The overall total of 18 directional lobes point in every primary axis direction and between every pair.

There are seven f orbitals, each with shapes more complex than those of the d orbitals.

Additionally, as is the case with the s orbitals, individual p, d, f and g orbitals with n values higher than the lowest possible value, exhibit an additional radial node structure which is reminiscent of harmonic waves of the same type, as compared with the lowest (or fundamental) mode of the wave. As with s orbitals, this phenomenon provides p, d, f, and g orbitals at the next higher possible value of n (for example, 3p orbitals vs. the fundamental 2p), an additional node in each lobe. Still higher values of n further increase the number of radial nodes, for each type of orbital.

The shapes of atomic orbitals in one-electron atom are related to 3-dimensional spherical harmonics. These shapes are not unique, and any linear combination is valid, like a transformation to cubic harmonics, in fact it is possible to generate sets where all the d's are the same shape, just like the and are the same shape.

The 1s, 2s, and 2p orbitals of a sodium atom.

Although individual orbitals are most often shown independent of each other, the orbitals coexist around the nucleus at the same time. Also, in 1927, Albrecht Unsöld proved that if one sums the electron density of all orbitals of a particular azimuthal quantum number ℓ of the same shell n (e.g., all three 2p orbitals, or all five 3d orbitals) where each orbital is occupied by an electron or each is occupied by an electron pair, then all angular dependence disappears; that is, the resulting total density of all the atomic orbitals in that subshell (those with the same ℓ) is spherical. This is known as Unsöld's theorem.

This table shows the real hydrogen-like wave functions for all atomic orbitals up to 7s, and therefore covers the occupied orbitals in the ground state of all elements in the periodic table up to radium and some beyond. "ψ" graphs are shown with − and + wave function phases shown in two different colors (arbitrarily red and blue). The orbital is the same as the orbital, but the and are formed by taking linear combinations of the and orbitals (which is why they are listed under the m = ±1 label). Also, the and are not the same shape as the , since they are pure spherical harmonics.

* No elements with 6f, 7d or 7f electrons have been discovered yet.

† Elements with 7p electrons have been discovered, but their electronic configurations are only predicted.

‡ For the elements whose highest occupied orbital is a 6d orbital, only some electronic configurations have been confirmed. ( Ds, Rg and Cn are still missing).

These are the real-valued orbitals commonly used in chemistry. Only the orbitals where are eigenstates of the orbital angular momentum operator, . The columns with are combinations of two eigenstates. See comparison in the following picture:

Atomic orbitals spdf m-eigenstates and superpositions

The shapes of atomic orbitals can be qualitatively understood by considering the analogous case of standing waves on a circular drum. To see the analogy, the mean vibrational displacement of each bit of drum membrane from the equilibrium point over many cycles (a measure of average drum membrane velocity and momentum at that point) must be considered relative to that point's distance from the center of the drum head. If this displacement is taken as being analogous to the probability of finding an electron at a given distance from the nucleus, then it will be seen that the many modes of the vibrating disk form patterns that trace the various shapes of atomic orbitals. The basic reason for this correspondence lies in the fact that the distribution of kinetic energy and momentum in a matter-wave is predictive of where the particle associated with the wave will be. That is, the probability of finding an electron at a given place is also a function of the electron's average momentum at that point, since high electron momentum at a given position tends to "localize" the electron in that position, via the properties of electron wave-packets (see the Heisenberg uncertainty principle for details of the mechanism).

This relationship means that certain key features can be observed in both drum membrane modes and atomic orbitals. For example, in all of the modes analogous to s orbitals (the top row in the animated illustration below), it can be seen that the very center of the drum membrane vibrates most strongly, corresponding to the antinode in all s orbitals in an atom. This antinode means the electron is most likely to be at the physical position of the nucleus (which it passes straight through without scattering or striking it), since it is moving (on average) most rapidly at that point, giving it maximal momentum.

A mental "planetary orbit" picture closest to the behavior of electrons in s orbitals, all of which have no angular momentum, might perhaps be that of a Keplerian orbit with the orbital eccentricity of 1 but a finite major axis, not physically possible (because particles were to collide), but can be imagined as a limit of orbits with equal major axes but increasing eccentricity.

Below, a number of drum membrane vibration modes and the respective wave functions of the hydrogen atom are shown. A correspondence can be considered where the wave functions of a vibrating drum head are for a two-coordinate system and the wave functions for a vibrating sphere are three-coordinate .

None of the other sets of modes in a drum membrane have a central antinode, and in all of them the center of the drum does not move. These correspond to a node at the nucleus for all non- s orbitals in an atom. These orbitals all have some angular momentum, and in the planetary model, they correspond to particles in orbit with eccentricity less than 1.0, so that they do not pass straight through the center of the primary body, but keep somewhat away from it.

In addition, the drum modes analogous to p and d modes in an atom show spatial irregularity along the different radial directions from the center of the drum, whereas all of the modes analogous to s modes are perfectly symmetrical in radial direction. The non-radial-symmetry properties of non- s orbitals are necessary to localize a particle with angular momentum and a wave nature in an orbital where it must tend to stay away from the central attraction force, since any particle localized at the point of central attraction could have no angular momentum. For these modes, waves in the drum head tend to avoid the central point. Such features again emphasize that the shapes of atomic orbitals are a direct consequence of the wave nature of electrons.

In atoms with one electron ( hydrogen-like atom), the energy of an orbital (and, consequently, any electron in the orbital) is determined mainly by . The orbital has the lowest possible energy in the atom. Each successively higher value of has a higher energy, but the difference decreases as increases. For high , the energy becomes so high that the electron can easily escape the atom. In single electron atoms, all levels with different within a given are degenerate in the Schrödinger approximation, and have the same energy. This approximation is broken slightly in the solution to the Dirac equation (where energy depends on n and another quantum number j), and by the effect of the magnetic field of the nucleus and quantum electrodynamics effects. The latter induce tiny binding energy differences especially for s electrons that go nearer the nucleus, since these feel a very slightly different nuclear charge, even in one-electron atoms; see Lamb shift.

In atoms with multiple electrons, the energy of an electron depends not only on its orbital, but also on its interactions with other electrons. These interactions depend on the detail of its spatial probability distribution, and so the energy levels of orbitals depend not only on but also on . Higher values of are associated with higher values of energy; for instance, the 2p state is higher than the 2s state. When , the increase in energy of the orbital becomes so large as to push the energy of orbital above the energy of the s orbital in the next higher shell; when the energy is pushed into the shell two steps higher. The filling of the 3d orbitals does not occur until the 4s orbitals have been filled.

The increase in energy for subshells of increasing angular momentum in larger atoms is due to electron-electron interaction effects, and it is specifically related to the ability of low angular momentum electrons to penetrate more effectively toward the nucleus, where they are subject to less screening from the charge of intervening electrons. Thus, in atoms with higher atomic number, the of electrons becomes more and more of a determining factor in their energy, and the principal quantum numbers of electrons becomes less and less important in their energy placement.

The energy sequence of the first 35 subshells (e.g., 1s, 2p, 3d, etc.) is given in the following table. Each cell represents a subshell with and given by its row and column indices, respectively. The number in the cell is the subshell's position in the sequence. For a linear listing of the subshells in terms of increasing energies in multielectron atoms, see the section below.

Note: empty cells indicate non-existent sublevels, while numbers in italics indicate sublevels that could (potentially) exist, but which do not hold electrons in any element currently known.

Electron atomic and molecular orbitals. The chart of orbitals (left) is arranged by increasing energy (see Madelung rule). Note that atomic orbits are functions of three variables (two angles, and the distance r from the nucleus). These images are faithful to the angular component of the orbital, but not entirely representative of the orbital as a whole.

Atomic orbitals and periodic table construction

Several rules govern the placement of electrons in orbitals (electron configuration). The first dictates that no two electrons in an atom may have the same set of values of quantum numbers (this is the Pauli exclusion principle). These quantum numbers include the three that define orbitals, as well as , or spin quantum number. Thus, two electrons may occupy a single orbital, so long as they have different values of s. However, only two electrons, because of their spin, can be associated with each orbital.

Additionally, an electron always tends to fall to the lowest possible energy state. It is possible for it to occupy any orbital so long as it does not violate the Pauli exclusion principle, but if lower-energy orbitals are available, this condition is unstable. The electron will eventually lose energy (by releasing a photon) and drop into the lower orbital. Thus, electrons fill orbitals in the order specified by the energy sequence given above.

This behavior is responsible for the structure of the periodic table. The table may be divided into several rows (called 'periods'), numbered starting with 1 at the top. The presently known elements occupy seven periods. If a certain period has number i, it consists of elements whose outermost electrons fall in the ith shell. Niels Bohr was the first to propose (1923) that the periodicity in the properties of the elements might be explained by the periodic filling of the electron energy levels, resulting in the electronic structure of the atom.

The periodic table may also be divided into several numbered rectangular ' blocks'. The elements belonging to a given block have this common feature: their highest-energy electrons all belong to the same ℓ-state (but the n associated with that ℓ-state depends upon the period). For instance, the leftmost two columns constitute the 's-block'. The outermost electrons of Li and Be respectively belong to the 2s subshell, and those of Na and Mg to the 3s subshell.

The following is the order for filling the "subshell" orbitals, which also gives the order of the "blocks" in the periodic table:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

The "periodic" nature of the filling of orbitals, as well as emergence of the s, p, d, and f "blocks", is more obvious if this order of filling is given in matrix form, with increasing principal quantum numbers starting the new rows ("periods") in the matrix. Then, each subshell (composed of the first two quantum numbers) is repeated as many times as required for each pair of electrons it may contain. The result is a compressed periodic table, with each entry representing two successive elements:

Although this is the general order of orbital filling according to the Madelung rule, there are exceptions, and the actual electronic energies of each element are also dependent upon additional details of the atoms (see Electron configuration § Atoms: Aufbau principle and Madelung rule).

The number of electrons in an electrically neutral atom increases with the atomic number. The electrons in the outermost shell, or valence electrons, tend to be responsible for an element's chemical behavior. Elements that contain the same number of valence electrons can be grouped together and display similar chemical properties.

For elements with high atomic number Z, the effects of relativity become more pronounced, and especially so for s electrons, which move at relativistic velocities as they penetrate the screening electrons near the core of high-Z atoms. This relativistic increase in momentum for high speed electrons causes a corresponding decrease in wavelength and contraction of 6s orbitals relative to 5d orbitals (by comparison to corresponding s and d electrons in lighter elements in the same column of the periodic table); this results in 6s valence electrons becoming lowered in energy.

Examples of significant physical outcomes of this effect include the lowered melting temperature of mercury (which results from 6s electrons not being available for metal bonding) and the golden color of gold and caesium.

In the Bohr model, an n = 1 electron has a velocity given by , where Z is the atomic number, is the fine-structure constant, and c is the speed of light. In non-relativistic quantum mechanics, therefore, any atom with an atomic number greater than 137 would require its 1s electrons to be traveling faster than the speed of light. Even in the Dirac equation, which accounts for relativistic effects, the wave function of the electron for atoms with is oscillatory and unbounded. The significance of element 137, also known as untriseptium, was first pointed out by the physicist Richard Feynman. Element 137 is sometimes informally called feynmanium (symbol Fy).[35] However, Feynman's approximation fails to predict the exact critical value of Z due to the non-point-charge nature of the nucleus and very small orbital radius of inner electrons, resulting in a potential seen by inner electrons which is effectively less than Z. The critical Z value, which makes the atom unstable with regard to high-field breakdown of the vacuum and production of electron-positron pairs, does not occur until Z is about 173. These conditions are not seen except transiently in collisions of very heavy nuclei such as lead or uranium in accelerators, where such electron-positron production from these effects has been claimed to be observed.

There are no nodes in relativistic orbital densities, although individual components of the wave function will have nodes.

pp hybridization (conjectured)

In late period 8 elements, a hybrid of 8p 3/2 and 9p 1/2 is expected to exist, where "3/2" and "1/2" refer to the total angular momentum quantum number. This "pp" hybrid may be responsible for the p-block of the period due to properties similar to p subshells in ordinary valence shells. Energy levels of 8p 3/2 and 9p 1/2 come close due to relativistic spin-orbit effects; the 9s subshell should also participate, as these elements are expected to be analogous to the respective 5p elements indium through xenon.

Bound quantum states have discrete energy levels. When applied to atomic orbitals, this means that the energy differences between states are also discrete. A transition between these states (i.e., an electron absorbing or emitting a photon) can thus happen only if the photon has an energy corresponding with the exact energy difference between said states.

Consider two states of the hydrogen atom:

By quantum theory, state 1 has a fixed energy of , and state 2 has a fixed energy of . Now, what would happen if an electron in state 1 were to move to state 2? For this to happen, the electron would need to gain an energy of exactly . If the electron receives energy that is less than or greater than this value, it cannot jump from state 1 to state 2. Now, suppose we irradiate the atom with a broad-spectrum of light. Photons that reach the atom that have an energy of exactly will be absorbed by the electron in state 1, and that electron will jump to state 2. However, photons that are greater or lower in energy cannot be absorbed by the electron, because the electron can jump only to one of the orbitals, it cannot jump to a state between orbitals. The result is that only photons of a specific frequency will be absorbed by the atom. This creates a line in the spectrum, known as an absorption line, which corresponds to the energy difference between states 1 and 2.

The atomic orbital model thus predicts line spectra, which are observed experimentally. This is one of the main validations of the atomic orbital model.

The atomic orbital model is nevertheless an approximation to the full quantum theory, which only recognizes many electron states. The predictions of line spectra are qualitatively useful but are not quantitatively accurate for atoms and ions other than those containing only one electron.

1. ^ Orchin, Milton; Macomber, Roger S.; Pinhas, Allan; Wilson, R. Marshall (2005). "1. Atomic Orbital Theory" (PDF). The Vocabulary and Concepts of Organic Chemistry (2nd ed.). Wiley. Archived (PDF) from the original on 9 October 2022.

2. ^ Atkins, Peter; de Paula, Julio; Friedman, Ronald (2009). Quanta, Matter, and Change: A Molecular Approach to Physical Chemistry. Oxford University Press. p. 106. ISBN 978-0-19-920606-3.

3. ^ Levine, Ira N. (1991). Quantum Chemistry (4th ed.). Prentice-Hall. p. 262. ISBN 0-205-12770-3. Therefore, the wave function of a system of identical interacting particles must not distinguish among the particles.

4. ^ Bohr, Niels (1913). "On the Constitution of Atoms and Molecules". Philosophical Magazine. 26 (1): 476. Bibcode:1914Natur..93..268N. doi:10.1038/093268a0. S2CID 3977652.

5. ^ Nagaoka, Hantaro (May 1904). "Kinetics of a System of Particles illustrating the Line and the Band Spectrum and the Phenomena of Radioactivity". Philosophical Magazine. 7 (41): 445-455. doi:10.1080/14786440409463141. Archived from the original on 27 November 2017.

6. ^ Thomson, J. J. (1904). "On the Structure of the Atom: an Investigation of the Stability and Periods of Oscillation of a number of Corpuscles arranged at equal intervals around the Circumference of a Circle; with Application of the Results to the Theory of Atomic Structure" (extract of paper). Philosophical Magazine. Series 6. 7 (39): 237-265. doi:10.1080/14786440409463107.

7. ^ Nagaoka, Hantaro (May 1904). "Kinetics of a System of Particles illustrating the Line and the Band Spectrum and the Phenomena of Radioactivity". Philosophical Magazine. 7 (41): 446. doi:10.1080/14786440409463141. Archived from the original on 27 November 2017.

8. ^ Heisenberg, W. (March 1927). "Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik". Zeitschrift für Physik A. 43 (3-4): 172-198. Bibcode:1927ZPhy...43..172H. doi:10.1007/BF01397280. S2CID 122763326.

9. ^ Bohr, Niels (April 1928). "The Quantum Postulate and the Recent Development of Atomic Theory". Nature. 121 (3050): 580-590. Bibcode:1928Natur.121..580B. doi:10.1038/121580a0.

10. ^ Blanco, Miguel A.; Flórez, M.; Bermejo, M. (December 1997). "Evaluation of the rotation matrices in the basis of real spherical harmonics". Journal of Molecular Structure: THEOCHEM. 419 (1-3): 19-27. doi:10.1016/S0166-1280(97)00185-1.

11. ^ Jeong, Jong Seok; Odlyzko, Michael L.; Xu, Peng; Jalan, Bharat; Mkhoyan, K. Andre (26 April 2016). "Probing core-electron orbitals by scanning transmission electron microscopy and measuring the delocalization of core-level excitations". Physical Review B. 93 (16): 165140. Bibcode:2016PhRvB..93p5140J. doi:10.1103/PhysRevB.93.165140.

12. ^ Poliakoff, Martyn; Tang, Samantha (9 February 2015). "The periodic table: icon and inspiration". Philosophical Transactions of the Royal Society A. 373 (2037): 20140211. Bibcode:2015RSPTA.37340211P. doi:10.1098/rsta.2014.0211. PMID 25666072.

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In atomic theory and quantum mechanics, an atomic orbital () is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus.

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From Wikipedia, the free encyclopedia

Yuri Tsolakovich Oganessian ( Russian: Юрий Цолакович Оганесян [ˈjʉrʲɪj t͡sɐˈlakəvʲɪt͡ɕ ɐgənʲɪˈsʲan]; born 14 April 1933) is a Russian-Armenian nuclear physicist who is considered the world's leading researcher in superheavy chemical elements. He led the discovery of many elements in the periodic table. He succeeded Georgy Flyorov as director of the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research in 1989 and is now its scientific leader. The heaviest element known in the periodic table, oganesson, is named after him, only the second time that an element was named after a living person (the other being seaborgium).

Yuri Tsolakovich Oganessian was born in Rostov-on-Don, Russia, on 14 April 1933 to Armenian parents. His father was from Iğdır (now in Turkey), while his mother was from Armavir in Russia's Krasnodar Krai. Oganessian spent his childhood in Yerevan, the capital of Soviet Armenia, where his family relocated in 1939. His father, Tsolak, a thermal engineer, was invited to work on the synthetic rubber plant in Yerevan. When the Eastern Front of World War II broke out, his family decided to not return to Rostov since it was occupied by Nazis. Yuri attended and finished school in Yerevan. He initially wanted to become a painter.

Oganessian was married to Irina Levonovna (1932-2010), a violinist and a music teacher in Dubna, with whom he had two daughters. As of 2017, his daughters resided in the US.

"A remarkable physicist and experimentalist... his work is characterised by originality, an ability to approach a problem from an unexpected side, and to achieve an ultimate result."

Oganessian moved to Russia, where he graduated from the Moscow Engineering Physics Institute (MEPhI) in 1956. He thereafter sought to join the Kurchatov Institute of Atomic Energy in Moscow, but as there were no vacancies left in Gersh Budker's team, he was instead recruited by Georgy Flyorov and began working at the Joint Institute for Nuclear Research (JINR) in Dubna, near Moscow.

He became director of the Flerov Laboratory of Nuclear Reactions at JINR in 1989, after Flerov retired, and remained in the position until 1996, when he was named the scientific leader of the Flerov.

Discovery of superheavy chemical elements

In the 1970s, Oganessian invented the "cold fusion" method (unrelated to the unproven energy-producing process cold fusion), a technique to produce transactinide elements (superheavy elements). It played a vital role in the discoveries of elements from 106 to 113. From the mid-1970s to the mid-1990s, the partnership of JINR, led by Oganessian, and the GSI Helmholtz Centre for Heavy Ion Research in Germany, led to the discovery of six chemical elements (107 to 112): bohrium, meitnerium, hassium, darmstadtium, roentgenium, and copernicium.

His newer technique, called "hot fusion" (also unrelated to nuclear fusion as an energy process), helped to discover elements 113 to 118, completing the seventh row of the periodic table. The technique involved bombarding calcium into targets containing heavier radioactive elements that are rich in neutrons at a cyclotron. The elements discovered using this method are nihonium (2003; also discovered by RIKEN in Japan using cold fusion), flerovium (1999), moscovium (2003), livermorium (2000), tennessine (2009), and oganesson (2002).

American chemist Sherry Yennello has called him the "grandfather of superheavy elements". Oganessian is the author of three discoveries, a monograph, 11 inventions, and more than 300 scientific papers.

In early 2016, science writers and bloggers speculated that one of the superheavy elements would be named oganessium or oganesson. The International Union of Pure and Applied Chemistry (IUPAC) announced in November 2016 that element 118 would be named oganesson to honor Oganessian. It was first observed in 2002 at JINR, by a joint team of Russian and American scientists. Headed by Oganessian, the team included American scientists of the Lawrence Livermore National Laboratory, California. Prior to this announcement, a dozen elements had been named after people, but of those, only seaborgium was likewise named while its namesake ( Glenn T. Seaborg) was alive. As Seaborg died in 1999, Oganessian is the only currently living namesake of an element.

Honors and awards

In 1990, he was elected Corresponding Member of the Soviet Academy of Sciences and in 2003 a Full Member (Academician) of the Russian Academy of Sciences.

Oganessian holds honorary degrees from Goethe University Frankfurt (2002), University of Messina (2009), and Yerevan State University. In 2019, he was elected as an Honorary Fellow of St Catharine's College, Cambridge.

State awards

Professional awards

Lomonosov Gold Medal (2018) "for fundamental research in the fields of interaction of complex nuclei and experimental evidence of existence of an 'island of stability' for superheavy elements"

UNESCO-Russia Mendeleev International Prize in the Basic Sciences (2021)

Recognition in Armenia

Oganessian was granted Armenian citizenship in July 2018 by Prime Minister Nikol Pashinyan. Oganessian is a member of the Board of Trustees of the Foundation for Armenian Science and Technology (FAST). He is also the chairman of the international scientific board of the Alikhanian National Science Laboratory (Yerevan Physics Institute). In 2017 HayPost issued a postage stamp dedicated to Oganessian. In 2022 the Central Bank of Armenia issued a silver commemorative coin dedicated to Oganessian and the element Oganesson (Og). In April 2022 he was named honorary professor of Yerevan State University.

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From Wikipedia, the free encyclopedia Yuri Tsolakovich Oganessian ( Russian: Юрий Цолакович Оганесян [ˈjʉrʲɪj t͡sɐˈlakəvʲɪt͡ɕ ɐgənʲɪˈsʲan]; born 14 April 1933) is a Russian-Armenian nuclear physicist who is considered the world's leading researcher in superheavy chemical elements. He led the discovery of many elements in the periodic table.

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The Joint Institute for Nuclear Research ( JINR, Russian: Объединённый институт ядерных исследований, ОИЯИ), in Dubna, Moscow Oblast (110 km north of Moscow), Russia, is an international research center for nuclear sciences, with 5500 staff members including 1200 researchers holding over 1000 Ph.Ds from eighteen countries. Most scientists, however, are eminent Russian scientists.

The institute has seven laboratories, each with its own specialisation: theoretical physics, high energy physics (particle physics), heavy ion physics, condensed matter physics, nuclear reactions, neutron physics, and information technology. The institute has a division to study radiation and radiobiological research and other ad hoc experimental physics experiments.

Principal research instruments include a nuclotron superconductive particle accelerator (particle energy: 7 GeV), three isochronous cyclotrons (120, 145, 650 MeV), a phasotron (680 MeV) and a synchrophasotron (4 GeV). The site has a neutron fast-pulse reactor (1500MW pulse) with nineteen associated instruments receiving neutron beams.

The Joint Institute for Nuclear Research was established on the basis of an agreement signed on March 26, 1956, in Moscow by representatives of the governments of the eleven founding countries, with a view to combining their scientific and material potential. The USSR contributed 50 percent, the People's Republic of China 20 percent. On February 1, 1957, JINR was registered by the United Nations. The institute is located in Dubna, 120 km north of Moscow.

At the time of the creation of JINR, the Institute of Nuclear Problems (INP) of the Academy of Sciences of the USSR already existed at the site of the future Dubna since the late 1940s, and it launched a program of fundamental and applied research at the synchrocyclotron. The Electrophysics Laboratory of the Academy of Sciences of the USSR (EFLAN) was established, and under the guidance of Academician Vladimir Veksler, work began to create a new accelerator - a proton synchrophasotron - with a record energy of 10 GeV at that time.

By the mid-1950s, there was a worldwide consensus that nuclear science should be accessible and that only broad cooperation could ensure the progressive development of this research, as well as the peaceful use of atomic energy. Thus, in 1954, near Geneva, CERN (European Organization for Nuclear Research) was established. At about the same time, the countries that belonged to the socialist community decided to establish a Joint Institute for Nuclear Research on the basis of the INP and EFLAN.

The first director of the United Institute was Professor D. I. Blokhintsev, who just completed the creation of Obninsk Nuclear Power Plant the world's first nuclear power plant in Obninsk. The first vice-directors of JINR were professors Marian Danysz (Poland) and V. Votruba (Czechoslovakia).

The history of the formation of the JINR is associated with the names of prominent scientists and Professors. The following list provides some of the names of prominent Scientists.

The JINR cooperates with many organizations. One of the main organizations with which JINR cooperates is UNESCO; its collaboration with JINR started in 1997 in order to develop basic sciences and try to achieve sustainable development. Joint activities include training programmes and grant mechanisms for researchers in the basic science. This international scientific cooperation and knowledge sharing in key scientific fields is one of the main 2030 UNESCO goals, the achievement of Sustainable Development. The United Nations General Assembly and UNESCO General Conference named 2019 as The International Year of the Periodic Table of Chemical Elements (IYPTE 2019); this reinforced the cooperation between this two organization. in addition, JINR is one of the observers of European Organization for Nuclear Research ( CERN).

The JINR members are 18 states:

Associate members are:

Scientific collaboration with organizations including:

The main fields of the institute's research are:

The JINR possess eight laboratories and University Centre.

The Superheavy Element Factory (SHE factory) at the JINR, opened in 2019, is a new experimental complex dedicated to superheavy element research. Its facilities enable a tenfold increase in beam intensity; such an increase in sensitivity enables the study of reactions with lower cross sections that would otherwise be inaccessible. Sergey Dmitriev, director of the Flerov Laboratory of Nuclear Reactions, believes that the SHE factory will enable closer examination of nuclei near the limits of stability, as well as experiments aimed at the synthesis of elements 119 and 120.

More than 40 major achievements in particle physics have been made through experiments at JINR. Including

JINR has instituted awards to honour and encourage high-level research in the fields of physics and mathematics since 1961.

The first award was dedicated to Wang Ganchang, deputy director from 1958 to 1960 and the Soviet Professor Vladimir Veksler for the discovery of antisigma-minus hyperon. The experimental group led by Professor Wang Ganchang, analysed more than 40,000 photographs which recorded tens of thousands of nuclear interactions taken in the propane bubble chamber, produced by the 10 GeV synchrophasotron used to bombard a target forming high energy mesons, was the first to discover the anti-sigma minus hyperon particles on March 9, 1959:

The discovery of this new unstable antiparticle which decays in (1.18±0.07)·10−10 s into an antineutron and a negative pion was announced in September of that year:[27]

No-one doubted at the time that this particle was elementary, but a few years later, this hyperon, the proton, the neutron, the pion and other hadrons had lost their status of elementary particles as they turned out to be complex particles too consisting of quarks and antiquarks.

Postage stamp of the USSR, 1976

Eduard Kozulin, head of group at the Laboratory of Nuclear Reactions, checking the experiment readiness of the super sensitive analyzer of heavy atoms mass.

a picture of JINR members

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Joint Institute for Nuclear Research - Wikipedia

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The Joint Institute for Nuclear Research ( JINR, Russian: Объединённый институт ядерных исследований, ОИЯИ), in Dubna, Moscow Oblast (110 km north of Moscow), Russia, is an international research center for nuclear sciences, with 5500 staff members including 1200 researchers holding over 1000 Ph.Ds from eighteen countries. Most scientists, however, are eminent Russian scientists.

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Superheavy elements, also known as transactinide elements, transactinides, or super-heavy elements, are the chemical elements with atomic number greater than 103. The superheavy elements are those beyond the actinides in the periodic table; the last actinide is lawrencium (atomic number 103). By definition, superheavy elements are also transuranium elements, i.e., having atomic numbers greater than that of uranium (92).

Glenn T. Seaborg first proposed the actinide concept, which led to the acceptance of the actinide series. He also proposed a transactinide series ranging from element 104 to 121 and a superactinide series approximately spanning elements 122 to 153 (although more recent work suggests the end of the superactinide series to occur at element 157 instead). The transactinide seaborgium was named in his honor.

Superheavy elements are radioactive and have only been obtained synthetically in laboratories. No macroscopic sample of any of these elements have ever been produced. Superheavy elements are all named after physicists and chemists or important locations involved in the synthesis of the elements.

IUPAC defines an element to exist if its lifetime is longer than 10 −14 second, which is the time it takes for the atom to form an electron cloud.

The known superheavy elements form part of the 6d and 7p series in the periodic table. Except for rutherfordium and dubnium, even the longest-lasting isotopes of superheavy elements have half-lives of minutes or less. The element naming controversy involved elements 102- 109. Some of these elements thus used systematic names for many years after their discovery was confirmed. (Usually the systematic names are replaced with permanent names proposed by the discoverers relatively shortly after a discovery has been confirmed.)

A superheavy atomic nucleus is created in a nuclear reaction that combines two other nuclei of unequal size into one; roughly, the more unequal the two nuclei in terms of mass, the greater the possibility that the two react. The material made of the heavier nuclei is made into a target, which is then bombarded by the beam of lighter nuclei. Two nuclei can only fuse into one if they approach each other closely enough; normally, nuclei (all positively charged) repel each other due to electrostatic repulsion. The strong interaction can overcome this repulsion but only within a very short distance from a nucleus; beam nuclei are thus greatly accelerated in order to make such repulsion insignificant compared to the velocity of the beam nucleus. The energy applied to the beam nuclei to accelerate them can cause them to reach speeds as high as one-tenth of the speed of light. However, if too much energy is applied, the beam nucleus can fall apart.

Coming close enough alone is not enough for two nuclei to fuse: when two nuclei approach each other, they usually remain together for approximately 10 −20 seconds and then part ways (not necessarily in the same composition as before the reaction) rather than form a single nucleus. This happens because during the attempted formation of a single nucleus, electrostatic repulsion tears apart the nucleus that is being formed. Each pair of a target and a beam is characterized by its cross section-the probability that fusion will occur if two nuclei approach one another expressed in terms of the transverse area that the incident particle must hit in order for the fusion to occur. This fusion may occur as a result of the quantum effect in which nuclei can tunnel through electrostatic repulsion. If the two nuclei can stay close for past that phase, multiple nuclear interactions result in redistribution of energy and an energy equilibrium.

The resulting merger is an excited state-termed a compound nucleus-and thus it is very unstable. To reach a more stable state, the temporary merger may fission without formation of a more stable nucleus. Alternatively, the compound nucleus may eject a few neutrons, which would carry away the excitation energy; if the latter is not sufficient for a neutron expulsion, the merger would produce a gamma ray. This happens in approximately 10 −16 seconds after the initial nuclear collision and results in creation of a more stable nucleus. The definition by the IUPAC/IUPAP Joint Working Party (JWP) states that a chemical element can only be recognized as discovered if a nucleus of it has not decayed within 10 −14 seconds. This value was chosen as an estimate of how long it takes a nucleus to acquire its outer electrons and thus display its chemical properties.

The beam passes through the target and reaches the next chamber, the separator; if a new nucleus is produced, it is carried with this beam. In the separator, the newly produced nucleus is separated from other nuclides (that of the original beam and any other reaction products) and transferred to a surface-barrier detector, which stops the nucleus. The exact location of the upcoming impact on the detector is marked; also marked are its energy and the time of the arrival. The transfer takes about 10 −6 seconds; in order to be detected, the nucleus must survive this long. The nucleus is recorded again once its decay is registered, and the location, the energy, and the time of the decay are measured.

Stability of a nucleus is provided by the strong interaction. However, its range is very short; as nuclei become larger, its influence on the outermost nucleons ( protons and neutrons) weakens. At the same time, the nucleus is torn apart by electrostatic repulsion between protons, and its range is not limited. Total binding energy provided by the strong interaction increases linearly with the number of nucleons, whereas electrostatic repulsion increases with the square of the atomic number, i.e. the latter grows faster and becomes increasingly important for heavy and superheavy nuclei. Superheavy nuclei are thus theoretically predicted and have so far been observed to predominantly decay via decay modes that are caused by such repulsion: alpha decay and spontaneous fission. Almost all alpha emitters have over 210 nucleons, and the lightest nuclide primarily undergoing spontaneous fission has 238. In both decay modes, nuclei are inhibited from decaying by corresponding energy barriers for each mode, but they can be tunnelled through.

Alpha particles are commonly produced in radioactive decays because mass of an alpha particle per nucleon is small enough to leave some energy for the alpha particle to be used as kinetic energy to leave the nucleus. Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning. As the atomic number increases, spontaneous fission rapidly becomes more important: spontaneous fission partial half-lives decrease by 23 orders of magnitude from uranium (element 92) to nobelium (element 102), and by 30 orders of magnitude from thorium (element 90) to fermium (element 100). The earlier liquid drop model thus suggested that spontaneous fission would occur nearly instantly due to disappearance of the fission barrier for nuclei with about 280 nucleons. The later nuclear shell model suggested that nuclei with about 300 nucleons would form an island of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half-lives. Subsequent discoveries suggested that the predicted island might be further than originally anticipated; they also showed that nuclei intermediate between the long-lived actinides and the predicted island are deformed, and gain additional stability from shell effects. Experiments on lighter superheavy nuclei, as well as those closer to the expected island, have shown greater than previously anticipated stability against spontaneous fission, showing the importance of shell effects on nuclei.

Alpha decays are registered by the emitted alpha particles, and the decay products are easy to determine before the actual decay; if such a decay or a series of consecutive decays produces a known nucleus, the original product of a reaction can be easily determined. (That all decays within a decay chain were indeed related to each other is established by the location of these decays, which must be in the same place.) The known nucleus can be recognized by the specific characteristics of decay it undergoes such as decay energy (or more specifically, the kinetic energy of the emitted particle). Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot be determined from its daughters.

The information available to physicists aiming to synthesize a superheavy element is thus the information collected at the detectors: location, energy, and time of arrival of a particle to the detector, and those of its decay. The physicists analyze this data and seek to conclude that it was indeed caused by a new element and could not have been caused by a different nuclide than the one claimed. Often, provided data is insufficient for a conclusion that a new element was definitely created and there is no other explanation for the observed effects; errors in interpreting data have been made.

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The heaviest element known at the end of the 19th century was uranium, with an atomic mass of approximately 240 (now known to be 238) amu. Accordingly, it was placed in the last row of the periodic table; this fueled speculation about the possible existence of elements heavier than uranium and why A = 240 seemed to be the limit. Following the discovery of the noble gases, beginning with that of argon in 1895, the possibility of heavier members of the group was considered. Danish chemist Julius Thomsen proposed in 1895 the existence of a sixth noble gas with Z = 86, A = 212 and a seventh with Z = 118, A = 292, the last closing a 32-element period containing thorium and uranium. In 1913, Swedish physicist Johannes Rydberg extended Thomsen's extrapolation of the periodic table to include even heavier elements with atomic numbers up to 460, but he did not believe that these superheavy elements existed or occurred in nature.

In 1914, German physicist Richard Swinne proposed that elements heavier than uranium, such as those around Z = 108, could be found in cosmic rays. He suggested that these elements may not necessarily have decreasing half-lives with increasing atomic number, leading to speculation about the possibility of some longer-lived elements at Z = 98-102 and Z = 108-110 (though separated by short-lived elements). Swinne published these predictions in 1926, believing that such elements might exist in the Earth's core, in iron meteorites, or in the ice caps of Greenland where they had been locked up from their supposed cosmic origin.

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Work performed from 1964 to 2013 at four labs - the Lawrence Berkeley National Laboratory in the US, the Joint Institute for Nuclear Research in the USSR (later Russia), the GSI Helmholtz Centre for Heavy Ion Research in Germany, and Riken in Japan - identified and confirmed the elements rutherfordium to oganesson according to the criteria of the IUPAC- IUPAP Transfermium Working Groups and subsequent Joint Working Parties. These discoveries complete the seventh row of the periodic table. The remaining two transactinides, ununennium ( Z = 119) and unbinilium ( Z = 120), have not yet been synthesized. They would begin an eighth period.

104 Rutherfordium, Rf (for Ernest Rutherford)

105 Dubnium, Db (for the town of Dubna, near Moscow)

106 Seaborgium, Sg (for Glenn T. Seaborg)

107 Bohrium, Bh (for Niels Bohr)

108 Hassium, Hs (for Hassia [Hesse], location of Darmstadt)

109 Meitnerium, Mt (for Lise Meitner)

110 Darmstadtium, Ds (for Darmstadt)

111 Roentgenium, Rg (for Wilhelm Röntgen)

112 Copernicium, Cn (for Nicolaus Copernicus)

113 Nihonium, Nh (for Nihon [Japan], location of the Riken institute)

114 Flerovium, Fl (for Russian physicist Georgy Flyorov)

115 Moscovium, Mc (for Moscow)

116 Livermorium, Lv (for Lawrence Livermore National Laboratory)

117 Tennessine, Ts (for Tennessee, location of Oak Ridge National Laboratory)

118 Oganesson, Og (for Russian physicist Yuri Oganessian)

Due to their short half-lives (for example, the most stable known isotope of seaborgium has a half-life of 14 minutes, and half-lives decrease gradually with increasing atomic number) and the low yield of the nuclear reactions that produce them, new methods have had to be created to determine their gas-phase and solution chemistry based on very small samples of a few atoms each. Relativistic effects become very important in this region of the periodic table, causing the filled 7s orbitals, empty 7p orbitals, and filling 6d orbitals to all contract inwards toward the atomic nucleus. This causes a relativistic stabilization of the 7s electrons and makes the 7p orbitals accessible in low excitation states.

Elements 103 to 112, lawrencium to copernicium, may be taken to form the 6d series of transition elements. Experimental evidence shows that elements 103-108 behave as expected for their position in the periodic table, as heavier homologues of lutetium through osmium. They are expected to have ionic radii between those of their 5d transition metal homologs and their actinide pseudohomologs: for example, Rf ⁴⁺ is calculated to have ionic radius 76 pm, between the values for Hf ⁴⁺ (71 pm) and Th ⁴⁺ (94 pm). Their ions should also be less polarizable than those of their 5d homologs. Relativistic effects are expected to reach a maximum at the end of this series, at roentgenium (element 111) and copernicium (element 112). Nevertheless, many important properties of the transactinides are still not yet known experimentally, though theoretical calculations have been performed.

Elements 113 to 118, nihonium to oganesson, should form a 7p series, completing the seventh period in the periodic table. Their chemistry will be greatly influenced by the very strong relativistic stabilization of the 7s electrons and a strong spin-orbit coupling effect "tearing" the 7p subshell apart into two sections, one more stabilized (7p 1/2, holding two electrons) and one more destabilized (7p 3/2, holding four electrons). Additionally, the 6d electrons are still destabilized in this region and hence may be able to contribute some transition metal character to the first few 7p elements. Lower oxidation states should be stabilized here, continuing group trends, as both the 7s and 7p 1/2 electrons exhibit the inert pair effect. These elements are expected to largely continue to follow group trends, though with relativistic effects playing an increasingly larger role. In particular, the large 7p splitting results in an effective shell closure at flerovium (element 114) and a hence much higher than expected chemical activity for oganesson (element 118).

Element 118 is the last element that has been synthesized. The next two elements, element 119 and element 120, should form an 8s series and be an alkali and alkaline earth metal respectively. The 8s electrons are expected to be relativistically stabilized, so that the trend toward higher reactivity down these groups will reverse and the elements will behave more like their period 5 homologs, rubidium and strontium. Still the 7p 3/2 orbital is still relativistically destabilized, potentially giving these elements larger ionic radii and perhaps even being able to participate chemically. In this region, the 8p electrons are also relativistically stabilized, resulting in a ground-state 8s ²8p ¹ valence electron configuration for element 121. Large changes are expected to occur in the subshell structure in going from element 120 to element 121: for example, the radius of the 5g orbitals should drop drastically, from 25 Bohr units in element 120 in the excited [Og] 5g ¹ 8s ¹ configuration to 0.8 Bohr units in element 121 in the excited [Og] 5g ¹ 7d ¹ 8s ¹ configuration, in a phenomenon called "radial collapse". Element 122 should add either a further 7d or a further 8p electron to element 121's electron configuration. Elements 121 and 122 should be similar to actinium and thorium respectively.

At element 121, the superactinide series is expected to begin, when the 8s electrons and the filling 8p 1/2, 7d 3/2, 6f 5/2, and 5g 7/2 subshells determine the chemistry of these elements. Complete and accurate calculations are not available for elements beyond 123 because of the extreme complexity of the situation: the 5g, 6f, and 7d orbitals should have about the same energy level, and in the region of element 160 the 9s, 8p 3/2, and 9p 1/2 orbitals should also be about equal in energy. This will cause the electron shells to mix so that the block concept no longer applies very well, and will also result in novel chemical properties that will make positioning these elements in a periodic table very difficult; element 164 is expected to mix characteristics of the elements of group 10, 12, and 18.

It has been suggested that elements beyond Z = 126 be called beyond superheavy elements.

Audi, G.; Kondev, F. G.; Wang, M.; et al. (2017). "The NUBASE2016 evaluation of nuclear properties". Chinese Physics C. 41 (3). 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
pp. 030001-1-030001-17, pp. 030001-18-030001-138, Table I. The NUBASE2016 table of nuclear and decay properties

Beiser, A. (2003). Concepts of modern physics (6th ed.). McGraw-Hill. ISBN 978-0-07-244848-1. OCLC 48965418.

Hoffman, D. C.; Ghiorso, A.; Seaborg, G. T. (2000). The Transuranium People: The Inside Story. World Scientific. ISBN 978-1-78-326244-1.

Kragh, H. (2018). From Transuranic to Superheavy Elements: A Story of Dispute and Creation. Springer. ISBN 978-3-319-75813-8.

Zagrebaev, V.; Karpov, A.; Greiner, W. (2013). "Future of superheavy element research: Which nuclei could be synthesized within the next few years?". Journal of Physics: Conference Series. 420 (1). 012001. arXiv:. Bibcode:2013JPhCS.420a2001Z. doi:10.1088/1742-6596/420/1/012001. ISSN 1742-6588.

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Superheavy elements, also known as transactinide elements, transactinides, or super-heavy elements, are the chemical elements with atomic number greater than 103. The superheavy elements are those beyond the actinides in the periodic table; the last actinide is lawrencium (atomic number 103). By definition, superheavy elements are also transuranium elements, i.e., having atomic numbers greater than that of uranium (92).

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A period 7 element is one of the chemical elements in the seventh row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases: a new row is b…

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The transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. All of these elements are synthetic, unstable and decay radioactively into other elements.

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The hexadecimal color code #680384 is a medium dark shade of magenta. In the RGB color model #680384 is comprised of 40.78% red, 1.18% green and 51.76% blue. In the HSL color space #680384 has a hue of 287° (degrees), 96% saturation and 26% lightness. This color has an approximate wavelength of 560.37 nm.
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# data[].attributes.attachment_link.description
The hexadecimal color code #680384 is a medium dark shade of magenta. In the RGB color model #680384 is comprised of 40.78% red, 1.18% green and 51.76% blue. In the HSL color space #680384 has a hue of 287° (degrees), 96% saturation and 26% lightness. This color has an approximate wavelength of 560.37 nm.

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Dmitri Ivanovich Mendeleev ( MEN-dəl-AY-əf;[2][b][a] 8 February [O.S. 27 January] 1834 – 2 February [O.S. 20 January] 1907) was a Russian chemist known for formulating the periodic law and creating a version of the periodic table of elements. He used the periodic law not only to correct the then-accepted properties of some known elements, such as the valence and atomic weight of uranium, but also to predict the properties of three elements that were yet to be discovered (germanium, gallium and scandium).

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http://www.scopeviews.co.uk/Tasco9TE-5.htm

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In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom is 1s ² 2s ² 2p ⁶, using the notation explained below.

Electronic configurations describe each electron as moving independently in an orbital, in an average field created by all other orbitals. Mathematically, configurations are described by Slater determinants or configuration state functions.

According to the laws of quantum mechanics, for systems with only one electron, a level of energy is associated with each electron configuration and in certain conditions, electrons are able to move from one configuration to another by the emission or absorption of a quantum of energy, in the form of a photon.

Knowledge of the electron configuration of different atoms is useful in understanding the structure of the periodic table of elements. This is also useful for describing the chemical bonds that hold atoms together. In bulk materials, this same idea helps explain the peculiar properties of lasers and semiconductors.

s (ℓ=0)

p (ℓ=1)

m=0

m=0

m=±1

s

pz

px

py

n=1

n=2

Electron configuration was first conceived under the Bohr model of the atom, and it is still common to speak of shells and subshells despite the advances in understanding of the quantum-mechanical nature of electrons.

An electron shell is the set of allowed states that share the same principal quantum number, n (the number before the letter in the orbital label), that electrons may occupy. An atom's nth electron shell can accommodate 2 n ² electrons, e.g. the first shell can accommodate 2 electrons, the second shell 8 electrons, the third shell 18 electrons and so on. The factor of two arises because the allowed states are doubled due to electron spin-each atomic orbital admits up to two otherwise identical electrons with opposite spin, one with a spin +1/2 (usually denoted by an up-arrow) and one with a spin −1/2 (with a down-arrow).

A subshell is the set of states defined by a common azimuthal quantum number, ℓ, within a shell. The values ℓ = 0, 1, 2, 3 correspond to the s, p, d, and f labels, respectively. For example, the 3 d subshell has n = 3 and ℓ = 2. The maximum number of electrons that can be placed in a subshell is given by 2(2ℓ+1). This gives two electrons in an s subshell, six electrons in a p subshell, ten electrons in a d subshell and fourteen electrons in an f subshell.

The numbers of electrons that can occupy each shell and each subshell arise from the equations of quantum mechanics, in particular the Pauli exclusion principle, which states that no two electrons in the same atom can have the same values of the four quantum numbers.

Physicists and chemists use a standard notation to indicate the electron configurations of atoms and molecules. For atoms, the notation consists of a sequence of atomic subshell labels (e.g. for phosphorus the sequence 1s, 2s, 2p, 3s, 3p) with the number of electrons assigned to each subshell placed as a superscript. For example, hydrogen has one electron in the s-orbital of the first shell, so its configuration is written 1s ¹. Lithium has two electrons in the 1s-subshell and one in the (higher-energy) 2s-subshell, so its configuration is written 1s ² 2s ¹ (pronounced "one-s-two, two-s-one"). Phosphorus ( atomic number 15) is as follows: 1s ² 2s ² 2p ⁶ 3s ² 3p ³.

For atoms with many electrons, this notation can become lengthy and so an abbreviated notation is used. The electron configuration can be visualized as the core electrons, equivalent to the noble gas of the preceding period, and the valence electrons: each element in a period differs only by the last few subshells. Phosphorus, for instance, is in the third period. It differs from the second-period neon, whose configuration is 1s ² 2s ² 2p ⁶, only by the presence of a third shell. The portion of its configuration that is equivalent to neon is abbreviated as [Ne], allowing the configuration of phosphorus to be written as [Ne] 3s ² 3p ³ rather than writing out the details of the configuration of neon explicitly. This convention is useful as it is the electrons in the outermost shell that most determine the chemistry of the element.

For a given configuration, the order of writing the orbitals is not completely fixed since only the orbital occupancies have physical significance. For example, the electron configuration of the titanium ground state can be written as either [Ar] 4s ² 3d ² or [Ar] 3d ² 4s ². The first notation follows the order based on the Madelung rule for the configurations of neutral atoms; 4s is filled before 3d in the sequence Ar, K, Ca, Sc, Ti. The second notation groups all orbitals with the same value of n together, corresponding to the "spectroscopic" order of orbital energies that is the reverse of the order in which electrons are removed from a given atom to form positive ions; 3d is filled before 4s in the sequence Ti ⁴⁺, Ti ³⁺, Ti ²⁺, Ti⁺, Ti.

The superscript 1 for a singly occupied subshell is not compulsory; for example aluminium may be written as either [Ne] 3s ² 3p ¹ or [Ne] 3s ² 3p. It is quite common to see the letters of the orbital labels (s, p, d, f) written in an italic or slanting typeface, although the International Union of Pure and Applied Chemistry (IUPAC) recommends a normal typeface (as used here). The choice of letters originates from a now-obsolete system of categorizing spectral lines as "sharp", "principal", "diffuse" and "fundamental" (or "fine"), based on their observed fine structure: their modern usage indicates orbitals with an azimuthal quantum number, l, of 0, 1, 2 or 3 respectively. After "f", the sequence continues alphabetically "g", "h", "i"... ( l = 4, 5, 6...), skipping "j", although orbitals of these types are rarely required.

The electron configurations of molecules are written in a similar way, except that molecular orbital labels are used instead of atomic orbital labels (see below).

Energy-ground state and excited states

The energy associated to an electron is that of its orbital. The energy of a configuration is often approximated as the sum of the energy of each electron, neglecting the electron-electron interactions. The configuration that corresponds to the lowest electronic energy is called the ground state. Any other configuration is an excited state.

As an example, the ground state configuration of the sodium atom is 1s ² 2s ² 2p ⁶ 3s ¹, as deduced from the Aufbau principle (see below). The first excited state is obtained by promoting a 3s electron to the 3p orbital, to obtain the 1s ² 2s ² 2p ⁶ 3p ¹ configuration, abbreviated as the 3p level. Atoms can move from one configuration to another by absorbing or emitting energy. In a sodium-vapor lamp for example, sodium atoms are excited to the 3p level by an electrical discharge, and return to the ground state by emitting yellow light of wavelength 589 nm.

Usually, the excitation of valence electrons (such as 3s for sodium) involves energies corresponding to photons of visible or ultraviolet light. The excitation of core electrons is possible, but requires much higher energies, generally corresponding to x-ray photons. This would be the case for example to excite a 2p electron of sodium to the 3s level and form the excited 1s ² 2s ² 2p ⁵ 3s ² configuration.

The remainder of this article deals only with the ground-state configuration, often referred to as "the" configuration of an atom or molecule.

Irving Langmuir was the first to propose in his 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his "concentric theory of atomic structure". Langmuir had developed his work on electron atomic structure from other chemists as is shown in the development of the History of the periodic table and the Octet rule. Niels Bohr (1923) incorporated Langmuir's model that the periodicity in the properties of the elements might be explained by the electronic structure of the atom. His proposals were based on the then current Bohr model of the atom, in which the electron shells were orbits at a fixed distance from the nucleus. Bohr's original configurations would seem strange to a present-day chemist: sulfur was given as 2.4.4.6 instead of 1s ² 2s ² 2p ⁶ 3s ² 3p ⁴ (2.8.6). Bohr used 4 and 6 following Alfred Werner's 1893 paper. In fact, the chemists believed in atoms long before the physicists. Langmuir began his paper referenced above by saying, "The problem of the structure of atoms has been attacked mainly by physicists who have given little consideration to the chemical properties which must ultimately be explained by a theory of atomic structure. The vast store of knowledge of chemical properties and relationships, such as is summarized by the Periodic Table, should serve as a better foundation for a theory of atomic structure than the relatively meager experimental data along purely physical lines... These electrons arrange themselves in a series of concentric shells, the first shell containing two electrons, while all other shells tend to hold eight." The valence electrons in the atom were described by Richard Abegg in 1904.

In 1924, E. C. Stoner incorporated Sommerfeld's third quantum number into the description of electron shells, and correctly predicted the shell structure of sulfur to be 2.8.6. However neither Bohr's system nor Stoner's could correctly describe the changes in atomic spectra in a magnetic field (the Zeeman effect).

Bohr was well aware of this shortcoming (and others), and had written to his friend Wolfgang Pauli to ask for his help in saving quantum theory (the system now known as " old quantum theory"). Pauli realized that the Zeeman effect must be due only to the outermost electrons of the atom, and was able to reproduce Stoner's shell structure, but with the correct structure of subshells, by his inclusion of a fourth quantum number and his exclusion principle (1925):

It should be forbidden for more than one electron with the same value of the main quantum number n to have the same value for the other three quantum numbers k [ l], j [] and m [].

The Schrödinger equation, published in 1926, gave three of the four quantum numbers as a direct consequence of its solution for the hydrogen atom: this solution yields the atomic orbitals that are shown today in textbooks of chemistry (and above). The examination of atomic spectra allowed the electron configurations of atoms to be determined experimentally, and led to an empirical rule (known as Madelung's rule (1936), see below) for the order in which atomic orbitals are filled with electrons.

The aufbau principle (from the German Aufbau, "building up, construction") was an important part of Bohr's original concept of electron configuration. It may be stated as:

a maximum of two electrons are put into orbitals in the order of increasing orbital energy: the lowest-energy orbitals are filled before electrons are placed in higher-energy orbitals.

The principle works very well (for the ground states of the atoms) for the first 18 elements, then decreasingly well for the following 100 elements. The modern form of the aufbau principle describes an order of orbital energies given by Madelung's rule (or Klechkowski's rule). This rule was first stated by Charles Janet in 1929, rediscovered by Erwin Madelung in 1936, and later given a theoretical justification by V.M. Klechkowski:

1. Orbitals are filled in the order of increasing n+l;

2. Where two orbitals have the same value of n+l, they are filled in order of increasing n.

This gives the following order for filling the orbitals:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, (8s, 5g, 6f, 7d, 8p, and 9s)

In this list the orbitals in parentheses are not occupied in the ground state of the heaviest atom now known ( Og, Z = 118).

The aufbau principle can be applied, in a modified form, to the protons and neutrons in the atomic nucleus, as in the shell model of nuclear physics and nuclear chemistry.

The form of the periodic table is closely related to the electron configuration of the atoms of the elements. For example, all the elements of group 2 have an electron configuration of [E] ns ² (where [E] is an inert gas configuration), and have notable similarities in their chemical properties. In general, the periodicity of the periodic table in terms of periodic table blocks is clearly due to the number of electrons (2, 6, 10, 14...) needed to fill s, p, d, and f subshells.

The outermost electron shell is often referred to as the "valence shell" and (to a first approximation) determines the chemical properties. It should be remembered that the similarities in the chemical properties were remarked on more than a century before the idea of electron configuration. It is not clear how far Madelung's rule explains (rather than simply describes) the periodic table, although some properties (such as the common +2 oxidation state in the first row of the transition metals) would obviously be different with a different order of orbital filling.

The aufbau principle rests on a fundamental postulate that the order of orbital energies is fixed, both for a given element and between different elements; in both cases this is only approximately true. It considers atomic orbitals as "boxes" of fixed energy into which can be placed two electrons and no more. However, the energy of an electron "in" an atomic orbital depends on the energies of all the other electrons of the atom (or ion, or molecule, etc.). There are no "one-electron solutions" for systems of more than one electron, only a set of many-electron solutions that cannot be calculated exactly (although there are mathematical approximations available, such as the Hartree-Fock method).

The fact that the aufbau principle is based on an approximation can be seen from the fact that there is an almost-fixed filling order at all, that, within a given shell, the s-orbital is always filled before the p-orbitals. In a hydrogen-like atom, which only has one electron, the s-orbital and the p-orbitals of the same shell have exactly the same energy, to a very good approximation in the absence of external electromagnetic fields. (However, in a real hydrogen atom, the energy levels are slightly split by the magnetic field of the nucleus, and by the quantum electrodynamic effects of the Lamb shift.)

The naïve application of the aufbau principle leads to a well-known paradox (or apparent paradox) in the basic chemistry of the transition metals. Potassium and calcium appear in the periodic table before the transition metals, and have electron configurations [Ar] 4s ¹ and [Ar] 4s ² respectively, i.e. the 4s-orbital is filled before the 3d-orbital. This is in line with Madelung's rule, as the 4s-orbital has n+ l = 4 ( n = 4, l = 0) while the 3d-orbital has n+ l = 5 ( n = 3, l = 2). After calcium, most neutral atoms in the first series of transition metals (Sc-Zn) have configurations with two 4s electrons, but there are two exceptions. Chromium and copper have electron configurations [Ar] 3d ⁵ 4s ¹ and [Ar] 3d ¹⁰ 4s ¹ respectively, i.e. one electron has passed from the 4s-orbital to a 3d-orbital to generate a half-filled or filled subshell. In this case, the usual explanation is that "half-filled or completely filled subshells are particularly stable arrangements of electrons".

The apparent paradox arises when electrons are removed from the transition metal atoms to form ions. The first electrons to be ionized come not from the 3d-orbital, as one would expect if it were "higher in energy", but from the 4s-orbital. This interchange of electrons between 4s and 3d is found for all atoms of the first series of transition metals. The configurations of the neutral atoms (K, Ca, Sc, Ti, V, Cr, ...) usually follow the order 1s, 2s, 2p, 3s, 3p, 4s, 3d, ...; however the successive stages of ionization of a given atom (such as Fe ⁴⁺, Fe ³⁺, Fe ²⁺, Fe⁺, Fe) usually follow the order 1s, 2s, 2p, 3s, 3p, 3d, 4s, ...

This phenomenon is only paradoxical if it is assumed that the energy order of atomic orbitals is fixed and unaffected by the nuclear charge or by the presence of electrons in other orbitals. If that were the case, the 3d-orbital would have the same energy as the 3p-orbital, as it does in hydrogen, yet it clearly doesn't. There is no special reason why the Fe ²⁺ ion should have the same electron configuration as the chromium atom, given that iron has two more protons in its nucleus than chromium, and that the chemistry of the two species is very different. Melrose and Eric Scerri have analyzed the changes of orbital energy with orbital occupations in terms of the two-electron repulsion integrals of the Hartree-Fock method of atomic structure calculation. More recently Scerri has argued that contrary to what is stated in the vast majority of sources including the title of his previous article on the subject, 3d orbitals rather than 4s are in fact preferentially occupied.

Similar ion-like 3d x4s ⁰ configurations occur in transition metal complexes as described by the simple crystal field theory, even if the metal has oxidation state 0. For example, chromium hexacarbonyl can be described as a chromium atom (not ion) surrounded by six carbon monoxide ligands. The electron configuration of the central chromium atom is described as 3d ⁶ with the six electrons filling the three lower-energy d orbitals between the ligands. The other two d orbitals are at higher energy due to the crystal field of the ligands. This picture is consistent with the experimental fact that the complex is diamagnetic, meaning that it has no unpaired electrons. However, in a more accurate description using molecular orbital theory, the d-like orbitals occupied by the six electrons are no longer identical with the d orbitals of the free atom.

Other exceptions to Madelung's rule

There are several more exceptions to Madelung's rule among the heavier elements, and as atomic number increases it becomes more and more difficult to find simple explanations such as the stability of half-filled subshells. It is possible to predict most of the exceptions by Hartree-Fock calculations, which are an approximate method for taking account of the effect of the other electrons on orbital energies. For the heavier elements, it is also necessary to take account of the effects of special relativity on the energies of the atomic orbitals, as the inner-shell electrons are moving at speeds approaching the speed of light. In general, these relativistic effects tend to decrease the energy of the s-orbitals in relation to the other atomic orbitals. The table below shows the ground state configuration in terms of orbital occupancy, but it does not show the ground state in terms of the sequence of orbital energies as determined spectroscopically. For example, in the transition metals, the 4s orbital is of a higher energy than the 3d orbitals; and in the lanthanides, the 6s is higher than the 4f and 5d. The ground states can be seen in the Electron configurations of the elements (data page).

The electron-shell configuration of elements beyond hassium has not yet been empirically verified, but they are expected to follow Madelung's rule without exceptions until element 120. Beyond element 120, Madelung's rule is expected to stop holding altogether due to the closeness in energy of the 5g, 6f, 7d, and 8p 1/2 orbitals.

In molecules, the situation becomes more complex, as each molecule has a different orbital structure. The molecular orbitals are labelled according to their symmetry, rather than the atomic orbital labels used for atoms and monatomic ions: hence, the electron configuration of the dioxygen molecule, O ₂, is written 1σ g ² 1σ u ² 2σ g ² 2σ u ² 3σ g ² 1π u ⁴ 1π g ², or equivalently 1σ g ² 1σ u ² 2σ g ² 2σ u ² 1π u ⁴ 3σ g ² 1π g ². The term 1π g ² represents the two electrons in the two degenerate π*-orbitals (antibonding). From Hund's rules, these electrons have parallel spins in the ground state, and so dioxygen has a net magnetic moment (it is paramagnetic). The explanation of the paramagnetism of dioxygen was a major success for molecular orbital theory.

The electronic configuration of polyatomic molecules can change without absorption or emission of a photon through vibronic couplings.

In a solid, the electron states become very numerous. They cease to be discrete, and effectively blend into continuous ranges of possible states (an electron band). The notion of electron configuration ceases to be relevant, and yields to band theory.

The most widespread application of electron configurations is in the rationalization of chemical properties, in both inorganic and organic chemistry. In effect, electron configurations, along with some simplified form of molecular orbital theory, have become the modern equivalent of the valence concept, describing the number and type of chemical bonds that an atom can be expected to form.

This approach is taken further in computational chemistry, which typically attempts to make quantitative estimates of chemical properties. For many years, most such calculations relied upon the " linear combination of atomic orbitals" (LCAO) approximation, using an ever-larger and more complex basis set of atomic orbitals as the starting point. The last step in such a calculation is the assignment of electrons among the molecular orbitals according to the Aufbau principle. Not all methods in calculational chemistry rely on electron configuration: density functional theory (DFT) is an important example of a method that discards the model.

For atoms or molecules with more than one electron, the motion of electrons are correlated and such a picture is no longer exact. A very large number of electronic configurations are needed to exactly describe any multi-electron system, and no energy can be associated with one single configuration. However, the electronic wave function is usually dominated by a very small number of configurations and therefore the notion of electronic configuration remains essential for multi-electron systems.

A fundamental application of electron configurations is in the interpretation of atomic spectra. In this case, it is necessary to supplement the electron configuration with one or more term symbols, which describe the different energy levels available to an atom. Term symbols can be calculated for any electron configuration, not just the ground-state configuration listed in tables, although not all the energy levels are observed in practice. It is through the analysis of atomic spectra that the ground-state electron configurations of the elements were experimentally determined.

1. ^ In formal terms, the quantum numbers n, ℓ and m ℓ arise from the fact that the solutions to the time-independent Schrödinger equation for hydrogen-like atoms are based on spherical harmonics.

2. ^ Langmuir, Irving (June 1919). "The Arrangement of Electrons in Atoms and Molecules". Journal of the American Chemical Society. 41 (6): 868-934. doi:10.1021/ja02227a002.

3. ^ Bohr, Niels (1923). "Über die Anwendung der Quantumtheorie auf den Atombau. I". Zeitschrift für Physik. 13 (1): 117. Bibcode:1923ZPhy...13..117B. doi:10.1007/BF01328209.

4. ^ Abegg, R. (1904). "Die Valenz und das periodische System. Versuch einer Theorie der Molekularverbindungen" [Valency and the periodic system. Attempt at a theory of molecular compounds]. Zeitschrift für Anorganische Chemie. 39 (1): 330-380. doi:10.1002/zaac.19040390125.

5. ^ Stoner, E.C. (1924). "The distribution of electrons among atomic levels". Philosophical Magazine. 6th Series. 48 (286): 719-36. doi:10.1080/14786442408634535.

6. ^ Pauli, Wolfgang (1925). "Über den Einfluss der Geschwindigkeitsabhändigkeit der elektronmasse auf den Zeemaneffekt". Zeitschrift für Physik. 31 (1): 373. Bibcode:1925ZPhy...31..373P. doi:10.1007/BF02980592. English translation from Scerri, Eric R. (1991). "The Electron Configuration Model, Quantum Mechanics and Reduction" (PDF). The British Journal for the Philosophy of Science. 42 (3): 309-25. doi:10.1093/bjps/42.3.309.

7. ^ Madelung, Erwin (1936). Mathematische Hilfsmittel des Physikers. Berlin: Springer.

8. ^ Wong, D. Pan (1979). "Theoretical justification of Madelung's rule". Journal of Chemical Education. 56 (11): 714-18. Bibcode:1979JChEd..56..714W. doi:10.1021/ed056p714.

9. The similarities in chemical properties and the numerical relationship between the ^ atomic weights of calcium, strontium and barium was first noted by Johann Wolfgang Döbereiner in 1817.

10. ^ Scerri, Eric R. (1998). "How Good Is the Quantum Mechanical Explanation of the Periodic System?" (PDF). Journal of Chemical Education. 75 (11): 1384-85. Bibcode:1998JChEd..75.1384S. doi:10.1021/ed075p1384. Ostrovsky, V.N. (2005). "On Recent Discussion Concerning Quantum Justification of the Periodic Table of the Elements". Foundations of Chemistry. 7 (3): 235-39. doi:10.1007/s10698-005-2141-y.

11. Electrons are ^ identical particles, a fact that is sometimes referred to as "indistinguishability of electrons". A one-electron solution to a many-electron system would imply that the electrons could be distinguished from one another, and there is strong experimental evidence that they can't be. The exact solution of a many-electron system is a n-body problem with n ≥ 3 (the nucleus counts as one of the "bodies"): such problems have evaded analytical solution since at least the time of Euler.

12. ^ There are some cases in the second and third series where the electron remains in an s-orbital.

13. ^ Melrose, Melvyn P.; Scerri, Eric R. (1996). "Why the 4s Orbital is Occupied before the 3d". Journal of Chemical Education. 73 (6): 498-503. Bibcode:1996JChEd..73..498M. doi:10.1021/ed073p498.

14. ^ Scerri, Eric (7 November 2013). "The trouble with the aufbau principle". Education in Chemistry. Vol. 50 no. 6. Royal Society of Chemistry. pp. 24-26. Archived from the original on 21 January 2018.

15. ^ Meek, Terry L.; Allen, Leland C. (2002). "Configuration irregularities: deviations from the Madelung rule and inversion of orbital energy levels". Chemical Physics Letters. 362 (5-6): 362-64. Bibcode:2002CPL...362..362M. doi:10.1016/S0009-2614(02)00919-3.

16. ^ Hoffman, Darleane C.; Lee, Diana M.; Pershina, Valeria (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer Science+Business Media. ISBN 978-1-4020-3555-5.

17. The labels are written in lowercase to indicate that they correspond to one-electron functions. They are numbered consecutively for each symmetry type (^ irreducible representation in the character table of the point group for the molecule), starting from the orbital of lowest energy for that type.

18. Miessler G.L. and Tarr D.A. ^ Inorganic Chemistry (2nd ed., Prentice Hall 1999) p.118 ISBN 0-13-841891-8

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In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom is 1s 2 2s 2 2p 6, using the notation explained below.

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Sweden Adopts the Grogorian Calendar (1753)

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Sweden Adopts the Grogorian Calendar (1753)

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The Gregorian calendar is the most widely used civil calendar in the world. It is named after Pope Gregory XIII, who introduced it in October 1582. The calendar spaces leap years to make the average year 365.2425 days long, approximating the 365.2422 day tropical year that is determined by the Earth's revolution around the Sun.

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As Nabokov pointed out himself, the title of John Shade's poem is from Shakespeare's Timon of Athens: "The moon's an arrant thief, / And her pale fire she snatches from the sun" (Act IV, scene 3).

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Timon of Athens ( The Life of Tymon of Athens) is a play by William Shakespeare, probably written in collaboration with Thomas Middleton in about 1605-1606, which was published in the First Folio in 1623. It is about the fortunes of an Athenian named Timon. The central character is a beloved citizen of Athens who through tremendous generosity spends his entire fortune on corrupt hangers-on only interested in getting the next payout.

The earliest-known production of the play was in 1674, when Thomas Shadwell wrote an adaptation under the title The History of Timon of Athens, The Man-hater. Multiple other adaptations followed over the next century, by writers such as Thomas Hull, James Love and Richard Cumberland. The straight Shakespearean text was performed at Smock Alley in Dublin in 1761, but adaptations continued to dominate the stage until well into the 20th century.

Timon of Athens was originally grouped with the tragedies, but some scholars name it one of the problem plays.

Timon: a lord and, later a misanthrope, of Athens.

Alcibiades: captain of a military brigade and good friend to Timon.

Apemantus, sometimes spelled Apermantus, a philosopher and churl.

Flavius is Timon's chief Steward.

Flaminius is one of Timon's servants.

Servilius is another of Timon's servants.

Lucilius is a romantic youth and Timon's servant.

Ventidius, also spelled "Ventidgius", is one of Timon's "friends" and is in debtors' prison.

Lucullus is Timon's "friend".

Lucius, Timon's "friend"

Sempronius is Timon's most jealous "friend".

Poet and Painter are friends, artists who seek Timon's patronage.

Jeweller and Merchant appear briefly

The Senators of Athens.

The Fool is briefly a companion to Apemantus.

Three Strangers, one named Hostilius; friends to Lucius.

The Old Athenian is the father of the woman Lucilius loves.

Four Lords. False friends of Timon.

Servants to Timon, Isidore, Lucullus, Lucius, Varro

Timon's creditors: Titus, Hortensius, Philotus. (Isidore and Varro are also creditors but only their servants appear.)

Phrynia. A prostitute.

Timandra. A prostitute.

Banditti, Soldier, Page, Cupid and Ladies at the Masque.

In the beginning, Timon is a wealthy and generous Athenian gentleman. He hosts a large banquet, attended by nearly all the main characters. Timon gives away money wastefully, and everyone wants to please him to get more, except for Apemantus, a churlish philosopher whose cynicism Timon cannot yet appreciate. He accepts art from Poet and Painter, and a jewel from the Jeweller, but by the end of Act 1 he has given that away to another friend. Timon's servant, Lucilius, has been wooing the daughter of an old Athenian. The man is angry, but Timon pays him three talents in exchange for the couple's being allowed to marry, because the happiness of his servant is worth the price. Timon is told that his friend, Ventidius, is in debtors' prison. He sends money to pay Ventidius's debt, and Ventidius is released and joins the banquet. Timon gives a speech on the value of friendship. The guests are entertained by a masque, followed by dancing. As the party winds down, Timon continues to give things away to his friends: his horses, as well as other possessions. The act is divided rather arbitrarily into two scenes, but the experimental and/or unfinished nature of the play is reflected in that it does not naturally break into a five-act structure.

Now Timon has given away all his wealth. Flavius, Timon's steward, is upset by the way Timon has spent his wealth, overextending his munificence by showering patronage on the parasitic writers and artists, and delivering his dubious friends from their financial straits; this he tells Timon when he returns from a hunt. Timon is upset that he has not been told this before, and begins to vent his anger on Flavius, who tells him that he has tried repeatedly in the past without success, and now he is at the end; Timon's land has been sold. Shadowing Timon is another guest at the banquet: the cynical philosopher Apemantus, who terrorises Timon's shallow companions with his caustic raillery. He was the only guest not angling for money or possessions from Timon. Along with a Fool, he attacks Timon's creditors when they show up to make their demands for immediate payment. Timon cannot pay, and sends out his servants to make requests for help from those friends he considers closest.

Timon's servants are turned down, one by one, by Timon's false friends, two giving lengthy monologues as to their anger with them. Elsewhere, one of Alcibiades's junior officers has reached an even further point of rage, killing a man in "hot blood." Alcibiades pleads with the Senate for mercy, arguing that a crime of passion should not carry as severe a sentence as premeditated murder. The senators disagree, and, when Alcibiades persists, banish him forever. He vows revenge, with the support of his troops. The act finishes with Timon discussing with his servants the revenge he will carry out at his next banquet.

Timon hosts a smaller party, intended only for those he feels have betrayed him. The serving trays are brought in, but under them the friends find rocks and lukewarm water. Timon sprays them with the water, throws the dishes at them, and flees his home. The loyal Flavius vows to find him.

Cursing the city walls, Timon goes into the wilderness and makes his crude home in a cave, sustaining himself on roots. Here he discovers an underground trove of gold. The knowledge of his discovery spreads. Alcibiades, Apemantus, and three bandits are able to find Timon before Flavius does. Accompanying Alcibiades are two prostitutes, Phrynia and Timandra, who trade barbs with the bitter Timon on the subject of venereal disease. Timon offers most of the gold to the rebel Alcibiades to subsidise his assault on the city, which he now wants to see destroyed, as his experiences have reduced him to misanthropy. He gives the rest to his whores to spread disease, and much of the remainder to Poet and Painter, who arrive soon after, leaving little for the senators who visit him. When Apemantus appears and accuses Timon of copying his pessimistic style there is a mutually misanthropic exchange of invective.

Flavius arrives. He wants the money as well, but he also wants Timon to come back into society. Timon acknowledges that he has had one true friend in Flavius, a shining example of an otherwise diseased and impure race, but laments that this man is a mere servant. He invites the last envoys from Athens, who hoped Timon might placate Alcibiades, to go hang themselves, and then dies in the wilderness. Alcibiades, marching on Athens, then throws down his glove, and ends the play reading the bitter epitaph Timon wrote for himself, part of which was composed by Callimachus:

"Here lies a wretched corpse of wretched soul bereft:
Seek not my name: a plague consume you wicked caitiffs left!"
Here lie I, Timon, who alive, all living men did hate,
Pass by, and curse thy fill, but pass and stay not here thy gait."

The play's date is uncertain, though its bitter tone links it with Coriolanus and John Day's play Humour Out of Breath, published in 1608, contains a reference to "the lord that gave all to his followers, and begged more for himself" - a possible allusion to Timon that would, if valid, support a date of composition before 1608. It has been proposed that Shakespeare himself took the role of the Poet, who has the fifth-largest line count in the play.

The play was entered into the Stationers' Register in 1623. There are no contemporary allusions to the play by which its date of composition may be determined, nor is there an agreed means of explaining the play's "loose ends and inconsistencies". Editors since the twentieth century have sought to remedy these defects through conjectures about Shakespeare's emotional development (Chambers); hypotheses concerning the play's "unfinished state" (Ellis-Fermor) and "scribal interference" (Oliver); and through statistical analyses of vocabulary, stage directions, and so forth.

Assuming the play is a collaboration between Shakespeare and Middleton, its date has been placed in the period 1605-1608, most likely 1606. In his 2004 edition for the Oxford Shakespeare, John Jowett argues the lack of act divisions in the Folio text is an important factor in determining a date. The King's Men only began to use act divisions in their scripts when they occupied the indoor Blackfriars Theatre in August 1608 as their winter playhouse. Timon is notoriously difficult to divide into acts, suggesting to Jowett that it was written at a time when act divisions were of no concern to the writer, hence it must have been written prior to August 1608. A terminus post quem may come from a possible topical allusion to the Gunpowder Plot of November 1605; "those that under hot ardent zeal would set whole realms on fire" (Sc.7.32-33). In the context of the play, the line is referring to religious zeal, but some scholars feel it is a subtle reference to the events of November. The play may also have been influenced by a pamphlet published in June 1605, Two Unnatural and Bloody Murders, which served as the primary source for Thomas Middleton's A Yorkshire Tragedy. This would narrow the possible range of dates to sometime between November 1605 and August 1608. Furthermore, MacDonald P. Jackson's rare-word test found the conjectured Shakespearean parts of the text date to 1605-1606. Going further, Jackson found that if one examines the non-Shakespearean sections in the context of Middleton's career, a date of 1605-1606 also results.

Shakespeare, in writing the play, probably drew upon the twenty-eighth novella of William Painter's Palace of Pleasure, the thirty-eighth novella of which was the main source for his All's Well That Ends Well. He also drew upon Plutarch's Lives, and perhaps Lucian's Dialogues and a lost comedy on the subject of Timon, allusions to which survive from 1584.

Since the nineteenth century, suggestions have been made that Timon is the work of two writers, and it has been argued that the play's unusual features are the result of the play being co-authored by playwrights with very different mentalities; the most popular candidate, Thomas Middleton, was first suggested in 1920.

The play contains several narrative inconsistencies uncharacteristic of Shakespeare, an unusually unsatisfying dénouement, drastically different styles in different places and an unusually large number of long lines that do not scan. One theory is that the play as it appears in the First Folio is unfinished. E. K. Chambers believes Shakespeare began the play, but abandoned it due to a mental breakdown, never returning to finish it. F. W. Brownlow believes the play to have been Shakespeare's last, and remained uncompleted at his death. The now-predominant theory of collaborative authorship was proposed by Charles Knight in 1838. Today, many scholars believe that other dramatist was Thomas Middleton. However, the exact nature of the collaboration is disputed. Did Middleton revise a piece begun by Shakespeare, did Shakespeare revise Middleton's work, or did they work together? John Jowett, editor of the play for both the Oxford Shakespeare: Complete Works and the individual Oxford Shakespeare edition, believes Middleton worked with Shakespeare in an understudy capacity and wrote scenes 2 (1.2 in editions which divide the play into acts), 5 (3.1), 6 (3.2), 7 (3.3), 8 (3.4), 9 (3.5), 10 (3.6) and the last eighty lines of 14 (4.3).

A 1917 study by J. M. Robertson posited that George Chapman wrote " A Lover's Complaint" and was the originator of Timon of Athens. These claims were rejected by other commentators, including Bertolt Brecht, Frank Harris, and Rolf Soellner (1979), who thought the play was a theatrical experiment. They argued that if one playwright revised another's play it would have been "fixed" to the standards of Jacobean theatre, which is clearly not the case. Soellner believed the play is unusual because it was written to be performed at the Inns of Court, where it would have found a niche audience with young lawyers.

Linguistic analyses of the text have all discovered apparent confirmation of the theory that Middleton wrote much of the play. It contains numerous words, phrases, and punctuation choices that are characteristic of his work but rare in Shakespeare. These linguistic markers cluster in certain scenes, apparently indicating that the play is a collaboration between Middleton and Shakespeare, not a revision of one's work by the other. The evidence suggests that Middleton wrote around one third of the play, mostly the central scenes. The editor of the Oxford edition, John Jowett, states that Middleton,

wrote the banquet scene (Sc. 2), the central scenes with Timon's creditors and Alcibiades' confrontation with the senate, and most of the episodes figuring the Steward. The play's abrasively harsh humour and its depiction of social relationships that involve a denial of personal relationships are Middletonian traits[.]

Jowett stresses that Middleton's presence does not mean the play should be disregarded, stating " Timon of Athens is all the more interesting because the text articulates a dialogue between two dramatists of a very different temper."

Many scholars find much unfinished about this play including unexplained plot developments, characters who appear unexplained and say little, prose sections that a polished version would have in verse (although close analysis would show this to be almost exclusively in the lines of Apemantus, and probably an intentional character trait), and the two epitaphs, one of which doubtless would have been cancelled in the final version. However, similar duplications appear in Julius Caesar and Love's Labour's Lost and are generally thought to be examples of two versions being printed when only one was ultimately used in production, which could easily be the case here. Frank Kermode refers to the play as "a poor relation of the major tragedies." This is the majority view, but the play has many scholarly defenders as well. Nevertheless, and perhaps unsurprisingly due to its subject matter, it has not proven to be among Shakespeare's popular works.

An anonymous play, Timon, also survives. Its Timon is explicitly hedonistic and spends his money much more on himself than in Shakespeare's version. He also has a mistress. It mentions a London inn called The Seven Stars that did not exist before 1602, yet it contains elements that are in Shakespeare's play but not in Plutarch or in Lucian's dialogue, Timon the Misanthrope, the other major accepted source for Shakespeare's play. Both Jacobean plays deal extensively with Timon's life before his flight into the wilderness, which in both Greek versions is given little more than one sentence each.

Soellner (1979) argues that the play is equal parts tragedy and satire, but that neither term can adequately be used as an adjective, for it is first and foremost a tragedy, and it does not satirise tragedy; rather, it satirises its subjects in the manner of Juvenalian satire while simultaneously being a tragedy.

Herman Melville considered Timon to be among the most profound of Shakespeare's plays, and in his 1850 review " Hawthorne and His Mosses" writes that Shakespeare is not "a mere man of Richard-the-Third humps, and Macbeth daggers," but rather "it is those deep far-away things in him; those occasional flashings-forth of the intuitive Truth in him; those short, quick probings at the very axis of reality: these are the things that make Shakespeare, Shakespeare. Through the mouths of the dark characters of Hamlet, Timon, Lear, and Iago, he craftily says, or sometimes insinuates the things, which we feel to be so terrifically true, that it were all but madness for any good man, in his own proper character, to utter, or even hint of them." In his 1590 Greene's Mourning Garment, Robert Greene used the term " Timonist" to refer to a lonely misanthrope. In his 1852 novel , Melville used the term " Timonism" about an artist's contemptuous rejection of both his audience and mankind in general.

Appreciation of the play often pivots on the reader's perception of Timon's asceticism. Admirers like Soellner point out that Shakespeare's text has Timon neither drink wine nor eat meat: only water and roots are specifically mentioned as being in his diet, which is also true of Apemantus, the philosopher. If one sees Timon's parties not as libations but as vain attempts to genuinely win friends among his peers, he gains sympathy. This is true of Pryce's Timon in the television version mentioned below, whose plate is explicitly shown as being perpetually unsoiled by food, and he tends to be meek and modest. This suggests a Timon who lives in the world but not of it. Other versions, often by creators who regard the play as a lesser work, involve jazz-era swinging (sometimes, such as in the Michael Langham/Brian Bedford production (in which Timon eats flamingo) set to a score that Duke Ellington composed for it in the 1960s), and conclude the first act with a debauchery. The Arkangel Shakespeare audio recording featuring Alan Howard (with Rodway reprising his television role) also takes this route: Howard's line readings suggest that Timon is getting drunker and drunker during the first act; he does not represent the moral or idealistic figure betrayed by the petty perceived by Soellner and Brecht the way Pryce does.

Major motifs in Timon include dogs,[clarification needed ] breath,[clarification needed ] gold (from Act IV on), and "use" (in the sense of usury). One of the most common emendations of the play is the Poet's line "Our Poesie Is as a Gowne, which uses From whence 'tis nourisht", to "our poesy is as a gum, which oozes from whence 'tis nourished" (originated by Pope and Johnson). Soellner says that such emendations erode the importance of this motif, and suggests a better emendation would be "from" to "form," creating a mixed metaphor "revelatory of the poet's inanity."

One odd emendation that often appears near the end of the play is Alcibiades commanding his troops to "cull th' infected fourth" from the Senate, as if he intends to destroy a fourth of the Senate. The word in the folio is, in fact, "forth", suggesting that "th' infected" are simply the ones who argued strongly against the cases of Timon and Alicibiades's officer, and that the troops are to leave alone those who just went along with it.

Banquets and feasting in Shakespeare are dramatically significant; besides sometimes being of central and structural importance, they often present dramatic spectacles in themselves. The first banquet of Timon of Athens reflects contemporary understandings of lavish Athenian entertainment at which Timon celebrates friendship and society. All the citizens are welcome to the banquet, as in accordance with the democratic principles of Athens. The second banquet functions as a parody of the first, as Timon uses it to exact revenge on his false friends, before abandoning feasting and the city completely by exiling himself. The senses are absent from this feast: Timon mocks the insatiable appetite of his guests as he uncovers dishes of smoke and water. Timon is misled by facades of friendship, and so inflicts apropos revenge: misleading those that had misled him by having them suffer the disillusionment of mortal senses with the mere spectacle of a banquet.

Shakespeare includes the character of Alcibiades in the play, the ultimate redeemer of iniquitous Athens. He would have been known among the educated of the audience for his presence at the Greek banquet in Plato's Symposium at which he gets the last word on the nature of love, proposing that it cannot be found in superficial appearance.

Performance history in Shakespeare's lifetime is unknown, though the same is also true of his more highly regarded plays such as Antony and Cleopatra and Coriolanus, which most scholars believe were written in the same period.

The earliest known performance of the straight Shakespearean text was at Smock Alley Theatre in Dublin in 1761. The earliest-known production of a predominantly Shakespearean version of the play in the United Kingdom was at Sadler's Wells in 1851.

It has played once on Broadway, in 1993, with Brian Bedford in the title role. This was a production of The Public Theater, which revived the play in February 2011 with Richard Thomas in the lead role, citing it as a play for the Great Recession.

The Chicago Shakespeare Theater first staged the play in 1997. It was the company's first modern-dress production. In April 2012, C.S.T. again staged the play with the Scottish actor Ian McDiarmid playing Timon. The play was given a new ending by director Barbara Gaines.

In August 2011, the Hudson Shakespeare Company of New Jersey staged Timon of Athens as part of their summer Shakespeare in the Parks series. As a departure from several other modern dress productions, director Jon Ciccarelli set the action in the " Roaring 20s" with corrupt politicians, mobsters and making the characters of Alcibiades, Timon of Athens and Flavius veterans of World War I. Timon (Imran Sheikh) was portrayed as a ' Great Gatsby' type figure who loses his great fortune to corrupt "friends".

In July 2012 the British National Theatre produced a version of the play set in modern dress and in the present time of scandal and fraud in the City of London and the British media. The play was directed by Nicholas Hytner. The National Theatre production was broadcast live to cinemas worldwide on 1 November 2012 as part of the National Theatre Live programme.

From 7 December 2018 to 22 February 2019 the play was revived by the Royal Shakespeare Company in a version directed by Simon Godwin, also in modern dress and featuring contemporary visual allusions, starring Kathryn Hunter as Lady Timon, one of several gender changes. Hunter and Godwin's version also had a run in New York City at Theatre for a New Audience in Brooklyn. The show opened on 19 January 2020, and ran through 9 February 2020. The following month the production played at the Shakespeare Theater Company's Kline Theatre in Washington DC.

Rarely performed, Timon of Athens was produced for TV as part of the BBC Television Shakespeare series in 1981 with Jonathan Pryce as Timon, Norman Rodway as Apemantus, John Welsh as Flavius, and John Shrapnel as Alcibiades, with Diana Dors as Timandra, Tony Jay as the Merchant, Sebastian Shaw as the Old Athenian, and John Fortune and John Bird as Poet and Painter. This Elizabethan/Jacobean historical period drama production was directed by Jonathan Miller.

I, Timon was released in 2016 premiered at the 2017 Hoboken International Film Festival (where it was nominated for "Best Director" and "Best Cinematography"). Bramwell Noah appears in the title role (and is also responsible for the original adaptation of the play for the big screen). The film also features a soundtrack based on the musical score Hexachordum Apollinis by Johann Pachelbel.

In 1678 Thomas Shadwell produced a popular adaptation, The History of Timon of Athens, the Man-Hater, to which Henry Purcell later composed the music. Shadwell added two women to the plot: Melissa, Timon's faithless fiancee, and Evandre, his loyal and discarded mistress. James Dance made another adaptation in 1768, soon followed by Richard Cumberland's version at Drury Lane in 1771, in which the dying Timon gives his daughter, Evadne, not present in Shakespeare's original, to Alcibiades.

Further adaptations followed in 1786 (Thomas Hull's at Covent Garden) and 1816 (George Lamb's at Drury Lane), ending with an 1851 production reinstating Shakespeare's original text by Samuel Phelps at Sadler's Wells.

Peter Brook directed a French language production in the sixties in which Timon was portrayed as an innocent idealist in a white tuxedo, ripped and dishevelled in the second part. His cast was primarily young, and Apemantus was Algerian. Commentators who admire the play typically see Timon as intended to have been a young man behaving in a naïve way. The play's detractors usually cite an oblique reference to armour in Act IV as evidence that Timon is a long-retired soldier.

British playwright Glyn Cannon wrote a short adaptation of the play called Timon's Daughter. It premiered in May, 2008 at the Old Fitzroy Theatre in Sydney. Cannon's play revisits the major themes of charity and giving in the original work, with a story that follows the adventures of Timon's daughter (named "Alice" in Cannon's play) when she is taken in by Flavius (renamed "Alan").

Shadwell's adaptation of the play was first performed with music by Louis Grabu in 1678. More famously, the 1695 revival had new music by Henry Purcell, most of it appearing in the masque that ended Act Two. Duke Ellington was commissioned to compose original music for the Stratford Shakespeare Festival's first production of Timon of Athens in 1963. Stephen Oliver, who wrote the incidental music for the BBC television version, composed a two-act opera, Timon of Athens, which was first performed at the Coliseum, London, on 17 May 1991. Singer/songwriter Ben Patton wrote and recorded a song named "Timon of Athens" in 2006 which is included on his album Because the Heart.

Ralph Waldo Emerson alludes to Timon in Essays: Second Series (1844) in an essay entitled "Gifts." Emerson says, "This giving is flat usurpation, and therefore when the beneficiary is ungrateful, as all beneficiaries hate all Timons ... I rather sympathize with the beneficiary, than with the anger of my lord Timon."

Karl Marx discusses and quotes Timon in his Economic and Philosophical Manuscripts of 1844 and Capital, Volume I. Marx's analysis focuses on how passages from Timon of Athens (Act IV, Scene III) shed light on the nature and amoral power of money:

"1. It is the visible divinity - the transformation of all human and natural properties into their contraries, the universal confounding and distorting of things: impossibilities are soldered together by it.

2. It is the common whore, the common procurer of people and nations."

Charlotte Brontë includes an allusion to Timon in (1853). Ginevra Fanshawe affectionately nicknames Lucy "Timon," which highlights Ginevra's role as a foil for Lucy. Herman Melville references Timon repeatedly in his novel The Confidence-Man (1857), when referring to confidence as a preferable trait in all circumstances to misanthropy. Charles Dickens alludes to Timon in Great Expectations (1861) when Wopsle moves to London to pursue a life in the theatre. Thomas Hardy alludes to Timon in his short story, The Three Strangers (1883).

The English artist and writer Wyndham Lewis produced one work of art, a portfolio of drawings titled "Timon of Athens" (1913), a preliminary example of the style of art that would come to be called Vorticist.

Danish author Karen Blixen ( Isak Dinesen) has a story within the tale titled "The Deluge of Norderney" in her Seven Gothic Tales (1934). It tells about a Hamlet-like figure, called Timon of Assens [], who comes from the Danish town of Assens.

Vladimir Nabokov borrowed the title for his novel (1962) from this quotation of Timon's in Act IV, Scene III:

The sun's a thief, and with his great attraction

Robs the vast sea: the moon's an arrant thief,

And her pale fire she snatches from the sun...

A copy of Timon of Athens features variously in the plot of Pale Fire and, at one point, the quotation above is amusingly mistranslated from the fictional language of Zemblan, a trademark prank of the polyglot Nabokov. The theme of thievery to which Timon is alluding is also a principal theme of Pale Fire, referring to Charles Kinbote's misappropriation of the poem by the deceased John Shade that forms part of the novel's structure.

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Timon of Athens ( The Life of Tymon of Athens) is a play by William Shakespeare, probably written in collaboration with Thomas Middleton in about 1605-1606, which was published in the First Folio in 1623. It is about the fortunes of an Athenian named Timon.

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Uppsala University appears in the novel S. by Doug Dorst and J. J. Abrams.

Abrams stated that the idea came from finding a book on a bench that had an inscription: "to whomever finds this book please read it and take it somewhere and leave it for someone else to read."

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Iris ( minor planet designation: 7 Iris) is a large main-belt asteroid and perhaps remnant planetesimal orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the asteroid belt. It is classified as an S-type asteroid, meaning that it has a stony composition.

Iris was discovered on August 13, 1847, by J. R. Hind from London, UK. It was Hind's first asteroid discovery and the seventh asteroid to be discovered overall.

Iris was named after the rainbow goddess Iris in Greek mythology, who was a messenger to the gods, especially Hera. Her quality of attendant of Hera was particularly appropriate to the circumstances of discovery, as Iris was spotted following 3 Juno by less than an hour of right ascension ( Juno is the Roman equivalent of Hera).

Iris's original symbol was a rainbow and a star: or more simply .

Iris is an S-type asteroid. The surface is bright and is probably a mixture nickel- iron metals and magnesium- and iron- silicates. Its spectrum is similar to that of L and LL chondrites with corrections for space weathering, so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites.

Among the S-type asteroids, Iris ranks fifth in geometric mean diameter after Eunomia, Juno, Amphitrite and Herculina. Its shape is consistent with an oblate spheroid with a large equatorial excavation, suggesting it is a remnant planetesimal. No collisional family can be associated with Iris, likely because the excavating impact occurred early in the history of the Solar System, and the debris has since dispersed.

Iris's bright surface and small distance from the Sun make it the fourth-brightest object in the asteroid belt after Vesta, Ceres, and Pallas. It has a opposition magnitude of +7.8, comparable to that of Neptune, and can easily be seen with binoculars at most oppositions. At typical oppositions it marginally outshines the larger though darker Pallas. But at rare oppositions near perihelion Iris can reach a magnitude of +6.7 (last time on October 31, 2017, reaching a magnitude of +6.9), which is as bright as Ceres ever gets.

A study by Hanus et al. using data from the VLT's SPHERE instrument names eight craters 20 to 40 km in diameter, and seven recurring features of unknown nature that remain nameless due to a lack of consistency and their occurrence on the edge of Iris. The names are Greek names of colors, corresponding to the rainbow as the sign of Iris. It is unknown whether these names are under consideration by the IAU. The other 7 features are labeled A through G.

Iris has a rotational period of 7.14 hours. Iris's north pole points towards the ecliptic coordinates (λ, β) estimated to be (18°, +19°) with a 4° uncertainty (Viikinkoski et al. 2017) or (19°, +26°) with a 3° uncertainty (Hanuš et al. 2019). This gives an axial tilt of xx°,[fix ] so that on much of each hemisphere, the sun does not set during summer, and does not rise during winter. On an airless body this gives rise to very large temperature differences.

Iris was observed occulting a star on May 26, 1995, and later on July 25, 1997. Both observations gave a diameter of about 200 km.

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Iris ( minor planet designation: 7 Iris) is a large main-belt asteroid and perhaps remnant planetesimal orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the asteroid belt. It is classified as an S-type asteroid, meaning that it has a stony composition.

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The iris ( pl.: irides or irises) is a thin, annular structure in the eye in most mammals and birds, responsible for controlling the diameter and size of the pupil, and thus the amount of light reaching the retina. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm. Eye color is defined by the iris.

The word "iris" is derived from the Greek word for " rainbow", also its goddess plus messenger of the gods in the , because of the many colours of this eye part.

The iris consists of two layers: the front pigmented fibrovascular layer known as a stroma and, beneath the stroma, pigmented epithelial cells.

The stroma is connected to a sphincter muscle ( sphincter pupillae), which contracts the pupil in a circular motion, and a set of dilator muscles ( dilator pupillae), which pull the iris radially to enlarge the pupil, pulling it in folds.

The iris (brown coloured portion of the eye) controls the size of the pupil by contracting the sphincter pupillae and dilator pupillae muscles

The sphincter pupillae is the opposing muscle of the dilator pupillae. The pupil's diameter, and thus the inner border of the iris, changes size when constricting or dilating. The outer border of the iris does not change size. The constricting muscle is located on the inner border.

The back surface is covered by a heavily pigmented epithelial layer that is two cells thick (the iris pigment epithelium), but the front surface has no epithelium. This anterior surface projects as the dilator muscles. The high pigment content blocks light from passing through the iris to the retina, restricting it to the pupil. The outer edge of the iris, known as the root, is attached to the sclera and the anterior ciliary body. The iris and ciliary body together are known as the anterior uvea. Just in front of the root of the iris is the region referred to as the trabecular meshwork, through which the aqueous humour constantly drains out of the eye, with the result that diseases of the iris often have important effects on intraocular pressure and indirectly on vision. The iris along with the anterior ciliary body provide a secondary pathway for aqueous humour to drain from the eye.

The iris is divided into two major regions:

1. The pupillary zone is the inner region whose edge forms the boundary of the pupil.

2. The ciliary zone is the rest of the iris that extends to its origin at the ciliary body.

The collarette is the thickest region of the iris, separating the pupillary portion from the ciliary portion. The collarette is a vestige of the coating of the embryonic pupil. It is typically defined as the region where the sphincter muscle and dilator muscle overlap. Radial ridges extend from the periphery to the pupillary zone, to supply the iris with blood vessels. The root of the iris is the thinnest and most peripheral.

The muscle cells of the iris are smooth muscle in mammals and amphibians, but are striated muscle in reptiles (including birds). Many fish have neither, and, as a result, their irises are unable to dilate and contract, so that the pupil always remains of a fixed size.

The crypts of Fuchs are a series of openings located on either side of the collarette that allow the stroma and deeper iris tissues to be bathed in aqueous humor. Collagen trabeculae that surround the border of the crypts can be seen in blue irises.

The midway between the collarette and the origin of the iris: These folds result from changes in the surface of the iris as it dilates.[citation needed ]

Crypts on the base of the iris are additional openings that can be observed close to the outermost part of the ciliary portion of the iris.[4]

The radial contraction folds of Schwalbe are a series of very fine radial folds in the pupillary portion of the iris extending from the pupillary margin to the collarette. They are associated with the scalloped appearance of the pupillary ruff.

The structural folds of Schwalbe are radial folds extending from the border of the ciliary and pupillary zones that are much broader and more widely spaced, continuous with the "valleys" between the ciliary processes.

Some of the circular contraction folds are a fine series of ridges that run near the pupillary margin and vary in thickness of the iris pigment epithelium; others are in ciliary portion of iris.[4]

Light micrograph of the iris near to the pupil. M. sph. sphincter muscle, L lens

Constriction of the pupil (miosis) observed by laser Doppler imaging reveals radial vessels of the iris.

A human eye demonstrating its owner's rare ability to voluntarily dilate and constrict his pupil on command, via voluntary control of his iris muscles.

Anterior chamber cross-section imaged by an SD-OCT.

From anterior (front) to posterior (back), the layers of the iris are:

The stroma and the anterior border layer of the iris are derived from the neural crest, and behind the stroma of the iris, the sphincter pupillae and dilator pupillae muscles, as well as the iris epithelium, develop from optic cup neuroectoderm.

The iris controls the size of the pupil by means of contracting the iris sphincter muscle and/or the iris dilator muscle. The size of the pupils is dependent on many factors (including light, emotional state, cognitive load, arousal, stimulation), and can range from less than 2 mm in diameter, to as large as 9 mm in diameter. However, there is considerable variation in maximal pupil diameter by individual humans, and decreases with age. The irises also contract the pupils when accommodation is initiated, to increase the depth of field.

Very few humans possess the ability to exert direct voluntary control over their iris muscles, which grants them the ability to dilate and constrict their pupils on command. However, there is no clear purpose or advantage to this.

Among human phenotypes, blue-green-gray eyes are a relatively rare[citation needed ] eye color and the exact color is often perceived to vary according to its surroundings.

The iris is usually strongly pigmented, with the color typically ranging between brown, hazel, green, gray, and blue. Occasionally, the color of the iris is due to a lack of pigmentation, as in the pinkish-white of oculocutaneous albinism, or to obscuration of its pigment by blood vessels, as in the red of an abnormally vascularised iris. Despite the wide range of colors, the only pigment that contributes substantially to normal iris color is the dark pigment melanin. The quantity of melanin pigment in the iris is one factor in determining the phenotypic eye color of an organism. Structurally, this huge molecule is only slightly different from its equivalent found in skin and hair. Iris color is due to variable amounts of eumelanin (brown/black melanins) and pheomelanin (red/yellow melanins) produced by melanocytes. More of the former is found in brown-eyed people and of the latter in blue- and green-eyed people. The limbal ring appears as a dark ring encircling the iris on some individuals, but is a result of the optical properties of the region between the cornea and sclera, not of pigments in the iris.

A light brown iris with prominent limbal ring. Light brown irises contain pheomelanin

Iris color is a highly complex phenomenon consisting of the combined effects of texture, pigmentation, fibrous tissue, and blood vessels within the iris stroma, which together make up an individual's epigenetic constitution in this context. An organism's "eye color" is actually the color of one's iris, the cornea being transparent and the white sclera entirely outside the area of interest.

Melanin is yellowish to dark hazel in the stromal pigment cells, and black in the iris pigment epithelium, which lies in a thin but very opaque layer across the back of the iris. Most human irises also show a condensation of the brownish stromal melanin in the thin anterior border layer, which by its position has an overt influence on the overall color. The degree of dispersion of the melanin, which is in subcellular bundles called melanosomes, has some influence on the observed color, but melanosomes in the iris of humans and other vertebrates are not mobile, and the degree of pigment dispersion cannot be reversed. Abnormal clumping of melanosomes does occur in disease and may lead to irreversible changes in iris color (see heterochromia, below). Colors other than brown or black are due to selective reflection and absorption from the other stromal components. Sometimes, lipofuscin, a yellow "wear and tear" pigment, also enters into the visible eye color, especially in aged or diseased green eyes.[citation needed ]

The optical mechanisms by which the nonpigmented stromal components influence eye color are complex, and many erroneous statements exist in the literature. Simple selective absorption and reflection by biological molecules ( hemoglobin in the blood vessels, collagen in the vessel and stroma) is the most important element. Rayleigh scattering and Tyndall scattering, (which also happen in the sky) and diffraction also occur. Raman scattering, and constructive interference, as in the feathers of birds, do not contribute to the color of the eye, but interference phenomena are important in the brilliantly colored iris pigment cells ( iridophores) in many animals. Interference effects can occur at both molecular and light-microscopic scales, and are often associated (in melanin-bearing cells) with quasicrystalline formations, which enhance the optical effects. Interference is recognised by characteristic dependence of color on the angle of view, as seen in eyespots of some butterfly wings, although the chemical components remain the same. White babies are usually born blue-eyed since no pigment is in the stroma, and their eyes appear blue due to scattering and selective absorption from the posterior epithelium. If melanin is deposited substantially, brown or black color is seen; if not, they will remain blue or gray.

All the contributing factors towards eye color and its variation are not fully understood. Autosomal recessive/dominant traits in iris color are inherent in other species, but coloration can follow a different pattern.

Example of heterochromia - one eye of the subject is brown, the other hazel.

Heterochromia (also known as a heterochromia iridis or heterochromia iridum) is an ocular condition in which one iris is a different color from the other iris (complete heterochromia), or where the part of one iris is a different color from the remainder (partial heterochromia or sectoral heterochromia). Uncommon in humans, it is often an indicator of ocular disease, such as chronic iritis or diffuse iris melanoma, but may also occur as a normal variant. Sectors or patches of strikingly different colors in the same iris are less common. Anastasius the First was dubbed dikoros (having two irises) for his patent heterochromia since his right iris had a darker color than the left one.

In contrast, heterochromia and variegated iris patterns are common in veterinary practice. Siberian Husky dogs show heterochromia,[better source needed ] possibly analogous to the genetically determined Waardenburg syndrome of humans. Some white cat fancies (e.g., white Turkish Angora or white Turkish van cats) may show striking heterochromia, with the most common pattern being one uniformly blue, the other copper, orange, yellow, or green. Striking variation within the same iris is also common in some animals, and is the norm in some species. Several herding breeds, particularly those with a blue merle coat color (such as Australian Shepherds and Border Collies) may show well-defined blue areas within a brown iris, as well as separate blue and darker eyes.[citation needed ] Some horses (usually within the white, spotted, palomino, or cremello groups of breeds) may show amber, brown, white and blue all within the same eye, without any sign of eye disease.[citation needed ]

One eye with a white or bluish-white iris is also known as a "walleye".

Iridology (also known as iridodiagnosis) is an alternative medicine technique whose proponents believe that patterns, colors, and other characteristics of the iris can be examined to determine information about a patient's systemic health. Practitioners match their observations to "iris charts", which divide the iris into zones corresponding to specific parts of the human body. Iridologists see the eyes as "windows" into the body's state of health.

Iridology is not supported by quality research studies, and is considered pseudoscience.

Fluorescein angiograpy of the iris reveals a radial layout of blood vessels.

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The iris ( pl.: irides or irises) is a thin, annular structure in the eye in most mammals and birds, responsible for controlling the diameter and size of the pupil, and thus the amount of light reaching the retina. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm.

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The Eye of Providence or the All-Seeing Eye of God ( Russian: "Всевидящее око Божие") is a type of orthodox icon that emerged in the Russian iconography in the 19th century. The image of the Eye of Providence, inscribed in a triangle, appeared in the paintings of the Russian Orthodox churches from the end of 18th century to the first half of 19th century, later in the Russian iconography, mostly among the Old Believers. It is a symbolic and allegorical composition of the words from the Holy Scripture that represents the omniscient and vigilant all-seeing eye of Christ.

This icon is a symbolic and allegorical composition of the words form the Bible: "Behold, the eyes of the Lord are on those who fear Him, on those who hope in His mercy." ( Psalms 33:18)

At the heart of the composition of such icons is the recurring motif of circles. In the central circle, Jesus Christ is depicted in the iconographic image of the Saviour Emmanuel with a blessing gesture. From this circle on the diagonal proceed 4 rays, on their tops are 4 small circles, inside of which are the allegorical symbols of the evangelists (see tetramorph), or less often, the images of the four evangelists themselves.

Fragments of the human face - eyes, nose and mouth are placed in the segments of the next circle. Above this circle on the central axis depicted the Virgin Mary with arms raised.

The next circle is green or red, it can represent the sky, sometimes starry. In the outermost circle usually depicted seraphim, or angels with scrolls. Above it on the central axis is a truncated circle, in which the heaven is depicted, God the Father with a gesture of blessing is seen in this circle. From God the Father emanates the Holy Spirit, descending in the form of a dove on the head of the Theotokos.

The inscriptions found in the icon:

Around the red face: "The Burning Coal appeared to Isaiah, the sun arose from the virgin's womb, bringing to those who wandered in darkness the light of the knowledge of God."

Around the green circle is the Ode of the Theotokos: "My soul magnifies the Lord, and my spirit has rejoiced in God my Savior. For He has regarded the lowly state of His maidservant." (Luke 1:46-48)

Around the blue circle: "Your eyes will be upon the faithful of the land, and greet them with cherubim who glorifying God."

Around God the Father and outermost circle is the Hymn of Victory: "Holy, holy, holy, the glory of the Lord of Hosts is full of heaven and earth."

Around the innermost circle is the Greater Doxology: "Glory to God in the highest, and on earth peace, goodwill toward men." (Luke 2:14)

Some modern clergymen do not approve the use of such icons. Metropolitan Hilarion considers that such icons "are not canonical, they do not correspond to any church text and believers should not pray in front of them."

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The Eye of Providence or the All-Seeing Eye of God ( Russian: "Всевидящее око Божие") is a type of orthodox icon that emerged in the Russian iconography in the 19th century.

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The Eye of Providence (or the all-seeing eye of God) is a symbol that depicts an eye, often enclosed in a triangle and surrounded by rays of light or Glory, meant to represent divine providence, whereby the eye of God watches over humanity. A well known example of the Eye of Providence appears on the reverse of the Great Seal of the United States, which is depicted on the United States one-dollar bill.

In 1782, the Eye of Providence was adopted as part of the symbolism featured on the reverse side of the Great Seal of the United States. It was first proposed as an element of the Great Seal by the first of three design committees in 1776, and is thought to be the suggestion of the artistic consultant, Pierre Eugene du Simitiere, and at the time, was a conventional symbol for God's benevolent oversight.

In his original proposal to the committee, Du Simitiere placed the Eye over shields so as to symbolize each of the original thirteen states of the Union. On the version of the seal that would eventually be approved, the Eye is positioned above an unfinished pyramid of thirteen steps (again symbolizing the original States, but also incorporating the nation's potential for future growth). Such symbolism is explained through the motto that appears above the Eye, annuit cœptis, meaning "He approves [our] undertakings" (or "has approved").

Perhaps due to its use in the design of the Great Seal, the Eye has made its way into other American seals and logos, such as, for example:

U.S. currency

The Eye of Providence has been used among various forms of currency throughout U.S. history, including:

The Eye of Providence appears on several Lithuanian insignia, including:

The Eye of Providence appears on the Coat of Arms of Brasłaŭ, Belarus, and of Wilamowice, Poland. The Eye was also part of the flag and coat of arms adopted by the Confederation of the Equator, a short lived 1824 secessionist revolt in the Northeastern provinces of Brazil. In the United Kingdom, the symbol was part of the Guards Division insignia, created in 1915.

In Estonia, the 50 krooni note shows the Eye as part of a depiction of the pipe organ of the Käina church. Likewise, the (old) 500 Ukrainian hryvnia note also depicts the Eye.

The Eye was included in the original publication of France's Declaration of the Rights of Man and of the Citizen, which also borrows iconography from the Ten Commandments. Similarly, the symbol is featured on the front page of the Constitution of Serbia from 1835.

Today, the Eye of Providence is often associated with Freemasonry, first appearing as part of the standard Freemason iconography in 1797 with the publication of Thomas Smith Webb's Freemasons Monitor.

In this use, the Eye, representing the all-seeing eye of God, serves as a reminder that humanity's thoughts and deeds are always observed by God-who is referred to in Masonry as the Great Architect of the Universe. Typically, the Masonic Eye of Providence has a semicircular glory below it, and is sometimes enclosed by a triangle.

Popular among conspiracy theorists is the claim that the Eye of Providence shown atop an unfinished pyramid on the Great Seal of the United States indicates the influence of Freemasonry in the founding of the United States. However, common Masonic use of the Eye dates to 14 years after the creation of the Great Seal. Furthermore, the only Mason among the members of the various design committees for the Great Seal was Benjamin Franklin, whose ideas for the seal were not adopted. Likewise, various Masonic organizations have explicitly denied any connection to the creation of the Seal.

The association of an eye with the concept of Divine Providence is found in Christianity. In late Renaissance European iconography, the Eye, surrounded by a triangle, was an explicit image of the Christian Trinity. The Eye of Providence was later painted over an image of three faces in Pontormo's 1525 Supper at Emmaus. Seventeenth-century depictions of the Eye sometimes show it surrounded by clouds or sunbursts. The Eye of God in a triangle is still used in church architecture and Christian art to symbolize the Trinity and God's omnipresence and divine providence.

The Eye of Providence is notably featured on the following Eastern Orthodox, Mormon, and Catholic buildings, among others:

Commonly in the context of a reference to the Illuminati, numerous video games, TV shows, films, books, and websites contain depictions of the Eye.

University/college insignia and logos of organisations

Several universities and college fraternities use the Eye of Providence in their coats of arms, seals, or badges, notably:

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The Eye of Providence (or the all-seeing eye of God) is a symbol that depicts an eye, often enclosed in a triangle and surrounded by rays of light or Glory, meant to represent divine providence, whereby the eye of God watches over humanity.

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A glory is an optical phenomenon, resembling an iconic saint's halo around the shadow of the observer's head, caused by sunlight or (more rarely) moonlight interacting with the tiny water droplets that comprise mist or clouds. The glory consists of one or more concentric, successively dimmer rings, each of which is red on the outside and bluish towards the centre. Due to its appearance, the phenomenon is sometimes mistaken for a circular rainbow, but the latter has a much larger diameter and is caused by different physical processes.

Glories arise due to wave interference of light internally refracted within small droplets.

Depending on circumstances (such as the uniformity of droplet size in the clouds), one or more of the glory's rings can be visible. The angular size of the inner and brightest ring is much smaller than that of a rainbow, about 5° to 20°, depending on the size of the droplets. In the right conditions, a glory and a rainbow can occur simultaneously.

Like a rainbow, a glory is centred on the antisolar (or, in case of the moon, antilunar) point, which coincides with the shadow of the observer's head. Since this point is by definition diametrically opposed to the sun's (or moon's) position in the sky, it always lies below the observer's horizon when the sun (or moon) is up. In order to see a glory, therefore, the clouds or fog causing it must be located below the observer, in a straight line with the Sun/Moon and the observer's eye. Hence, the glory is commonly observed from a high viewpoint such as a mountain, tall building or from an aircraft. In the latter case, if the plane is flying sufficiently low for its shadow to be visible on the clouds, the glory always surrounds it. This is sometimes called The Glory of the Pilot.

Brocken spectre

When viewed from a mountain or tall building, glories are often seen in association with a Brocken spectre, also called Mountain spectre, the apparently enormously magnified shadow of an observer, cast (when the sun is low) on clouds below the mountain on which the viewer is standing. The name derives from the Brocken, the tallest peak of the Harz mountain range in Germany. Because the peak is above the cloud level and the area is frequently misty, conditions conducive to casting a shadow on a cloud layer are common. Giant shadows that seemed to move by themselves due to movement of the cloud layer (this movement is another part of the definition of the Brocken spectre), and that were surrounded by glories, may have contributed to the reputation the Harz mountains hold as a refuge for witches and evil spirits. In Goethe's Faust, the Brocken is called the Blocksberg and is the site of the Witches' Sabbath on Walpurgis Night.

Modern theories of light, first described by Henri Poincaré in 1887, are able to explain the phenomenon of glories through the complex angular momentum (rotation) of the electromagnetic field of a light wave, and do not need quantum theories. A summary of rainbow-like phenomenon was provided in Scientific American in 1977, and states:

It is gratifying to discover in the elegant but seemingly abstract theory of complex angular momentum an explanation for these two natural phenomena [Glories and 10th order Rainbows], and to find there an unexpected link between them.

Most 20th century work on the phenomenon of rainbows and glories has focused on determining the correct intensity of light at each point in the phenomenon, which does require quantum theories. In 1947, the Dutch astronomer Hendrik van de Hulst suggested that surface waves are involved. He speculated that the brightness of the coloured rings of the glory are caused by two-ray interference between "short" and "long" path surface waves-which are generated by light rays entering the droplets at diametrically opposite points (both rays suffer one internal reflection). A theory by Brazilian physicist Herch Moysés Nussenzveig suggests that the light energy beamed back by a glory originates mostly from classical wave tunneling (synonymous in the paper to the evanescent wave coupling), which is an interaction between an evanescent light wave traveling along the surface of the drop and the waves inside the drop.

C. T. R. Wilson saw a glory while working as a temporary observer at the Ben Nevis weather station. Inspired by the impressive sight, he decided to build a device for creating clouds in the laboratory, so that he could make a synthetic, small-scale glory. His work led directly to the cloud chamber, a device for detecting ionizing radiation for which he and Arthur Compton received the Nobel Prize for Physics in 1927.

In China, the phenomenon is called Buddha's light (or halo). It is often observed on cloud-shrouded high mountains, such as Huangshan and Mount Emei. Records of the phenomenon at Mount Emei date back to A.D. 63. The colourful halo always surrounds the observer's own shadow, and thus was often taken to show the observer's personal enlightenment (associated with Buddha or divinity).[citation needed ]

Stylized glories appear occasionally in Western heraldry. Two glories appear on the Great Seal of the United States: A glory breaking through clouds surrounding a cluster of 13 stars on the obverse, and a glory surrounding the Eye of Providence surmounting an unfinished pyramid on the reverse.[citation needed ]

Mayes, Lawrence (1 September 2003), Glories - an Atmospheric Phenomenon, archived from the original on 16 August 2007

Nussenzveig, H. Moysés (January 2012), "The Science of the Glory", Scientific American, 306 (1): 68-73, doi:10.1038/scientificamerican0112-68, PMID 22279838

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A glory is an optical phenomenon, resembling an iconic saint's halo around the shadow of the observer's head, caused by sunlight or (more rarely) moonlight interacting with the tiny water droplets that comprise mist or clouds. The glory consists of one or more concentric, successively dimmer rings, each of which is red on the outside and bluish towards the centre.

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The Moon is Earth's only natural satellite. It orbits at an average distance of (), about 30 times the planet's diameter. Being tidally locked, it always faces Earth with its near side. This results in the lunar month of 29.5 days matching the lunar day. Exerting gravitational force on Earth, it and to a lesser extent the Sun are the main drivers of the tides.

The Moon is in geophysical terms a planetary-mass object or satellite planet. It has a mass that amounts to 1.2% of Earth's, and a diameter that is roughly one-quarter of Earth's or with 3,474 km (2,159 mi) about as wide as Australia. Within the Solar System it is the most massive and largest satellite in relation to its parent planet, the fifth most massive and largest moon overall, and more massive and larger than all known dwarf planets. Its surface gravity is about one sixth of Earth's, about half of that of Mars, and after Jupiter's moon Io the second highest among all Solar System moons. The body of the Moon is differentiated and terrestrial, with no significant hydrosphere, atmosphere, or magnetic field. It formed 4.51 billion years ago, not long after Earth's formation, out of the debris from a giant impact between Earth and a hypothesized Mars-sized body called Theia.

The lunar surface is covered in lunar dust and marked by mountains, impact craters, their ejecta, ray-like streaks and, mostly on the near side of the Moon, by dark maria ("seas"), which are plains of cooled magma. These maria formed when large impacts on the far side of the Moon heated up low lying layers of its crust on the near side. The Moon is, beside when passing through Earth's shadow during a lunar eclipse, always illuminated by the Sun, but from Earth the visible illumination shifts during its orbit, producing the lunar phases. The Moon is the brightest celestial object in Earth's night sky. This is mainly due to its large angular diameter, while the reflectance of the lunar surface is comparable to that of asphalt. The apparent size is nearly the same as that of the Sun, allowing it to cover the Sun almost completely during a total solar eclipse. From Earth about 59% of the lunar surface is visible over time due to cyclical shifts in perspective ( libration), making parts of the far side of the Moon visible.

For humans the Moon has been an important source of inspiration and knowledge, having been crucial to cosmography, mythology, religion, art, time keeping, natural science, and spaceflight. On September 13, 1959 the first human-made object to reach an extraterrestrial body arrived on the Moon, the Soviet Union's Luna 2 impactor. In 1966 the Moon became the first extraterrestrial body where soft landings and orbital insertions were achieved. On July 20, 1969, humans for the first time landed on the Moon and any extraterrestrial body, at Mare Tranquillitatis with the lander of the United States' Apollo 11 mission. Five more crews were sent between then and 1972, each with two men landing on the surface. The longest stay was 75 hours by the Apollo 17 crew. Thereafter exploration of the Moon has continued robotically, with crewed missions being planned to return starting in the late 2020s.

Names and etymology

The usual English proper name for Earth's natural satellite is simply Moon, with a capital M. The noun moon is derived from Old English mōna, which (like all its Germanic cognates) stems from Proto-Germanic *mēnōn, which in turn comes from Proto-Indo-European *mēnsis "month" (from earlier *mēnōt, genitive *mēneses) which may be related to the verb "measure" (of time).

Occasionally, the name Luna is used in scientific writing and especially in science fiction to distinguish the Earth's moon from others, while in poetry "Luna" has been used to denote personification of the Moon. Cynthia is another poetic name, though rare, for the Moon personified as a goddess, while (literally "Moon") is the Greek goddess of the Moon.

The English adjective pertaining to the Moon is "lunar", derived from the Latin word for the Moon, lūna. Selenian is an adjective used to describe the Moon as a world, rather than as a celestial object, but its use is rare. It is derived from selēnē, the Greek word for the Moon, and its cognate selenic was originally a rare synonym but now nearly always refers to the chemical element selenium. The element name selenium and the prefix seleno- (as in selenography, the study of the physical features of the Moon) come from this Greek word.

The Greek goddess of the wilderness and the hunt, Artemis, equated with the Roman Diana, one of whose symbols was the Moon and who was often regarded as the goddess of the Moon, was also called Cynthia, from her legendary birthplace on Mount Cynthus. These names - Luna, Cynthia and Selene - are reflected in technical terms for lunar orbits such as apolune, pericynthion and selenocentric.

The astronomical symbol for the Moon is a crescent, , for example in M☾ 'lunar mass' (also ML).

Natural history

Lunar geologic timescale
Millions of years before present

The lunar geological periods are named after their characteristic features, from most impact craters outside the dark mare, to the mare and later craters, and finally the young, still bright and therefore readily visible craters with ray systems like Copernicus or Tycho.

The far side of the Moon, lacking the near side's characteristic large dark areas of maria, resembling how the near side of the Moon might have looked early in the Moon's history[35][36]

Isotope dating of lunar samples suggests the Moon formed around 50 million years after the origin of the Solar System. Historically, several formation mechanisms have been proposed, but none satisfactorily explains the features of the Earth-Moon system. A fission of the Moon from Earth's crust through centrifugal force would require too great an initial rotation rate of Earth. Gravitational capture of a pre-formed Moon depends on an unfeasibly extended atmosphere of Earth to dissipate the energy of the passing Moon. A co-formation of Earth and the Moon together in the primordial accretion disk does not explain the depletion of metals in the Moon. None of these hypotheses can account for the high angular momentum of the Earth-Moon system.

The prevailing theory is that the Earth-Moon system formed after a giant impact of a Mars-sized body (named ) with the proto-Earth. The oblique impact blasted material into orbit about the Earth and the material accreted and formed the Moon just beyond the Earth's Roche limit of ~.

Giant impacts are thought to have been common in the early Solar System. Computer simulations of giant impacts have produced results that are consistent with the mass of the lunar core and the angular momentum of the Earth-Moon system. These simulations show that most of the Moon derived from the impactor, rather than the proto-Earth. However, models from 2007 and later suggest a larger fraction of the Moon derived from the proto-Earth. Other bodies of the inner Solar System such as Mars and Vesta have, according to meteorites from them, very different oxygen and tungsten isotopic compositions compared to Earth. However, Earth and the Moon have nearly identical isotopic compositions. The isotopic equalization of the Earth-Moon system might be explained by the post-impact mixing of the vaporized material that formed the two, although this is debated.

The impact would have released enough energy to liquefy both the ejecta and the Earth's crust, forming a magma ocean. The liquefied ejecta could have then re-accreted into the Earth-Moon system. The newly formed Moon would have had its own lunar magma ocean; its depth is estimated from about 500 km (300 miles) to 1,737 km (1,079 miles).

While the giant-impact theory explains many lines of evidence, some questions are still unresolved, most of which involve the Moon's composition. Models that have the Moon acquiring a significant amount of the proto-earth are more difficult to reconcile with geochemical data for the isotopes of zirconium, oxygen, silicon, and other elements. Above a high resolution threshold for simulations, [clarify ] a study published in 2022 finds that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside Earth's Roche limit. Even satellites that initially pass within the Roche limit can reliably and predictably survive, by being partially stripped and then torqued onto wider, stable orbits.

Natural development

Artist's depiction of the Moon as it might have appeared in Earth's sky after the Late Heavy Bombardment around 4 billion years ago, when its orbit was half as close to Earth and it appeared 2.8 times larger than today.[59]

The newly formed Moon settled into a much closer Earth orbit than it has today. Each body therefore appeared much larger in the sky of the other, eclipses were more frequent, and tidal effects were stronger. Due to tidal acceleration, the Moon's orbit around Earth has become significantly larger, with a longer period.

Following formation, the Moon has cooled and most of its atmosphere has been stripped. The lunar surface has since been shaped by large impact events and many small ones, forming a landscape featuring craters of all ages.

The Moon was volcanically active until 1.2 billion years ago, which laid down the prominent lunar maria. Most of the mare basalts erupted during the Imbrian period, 3.3-3.7 billion years ago, though some are as young as 1.2 billion years and some as old as 4.2 billion years. There are differing explanations for the eruption of mare basalts, particularly their uneven occurrence which mainly appear on the near-side. Causes of the distribution of the lunar highlands on the far side are also not well understood. Topological measurements show the near side crust is thinner than the far side. One possible scenario then is that large impacts on the near side may have made it easier for lava to flow onto the surface.

Physical characteristics

The Moon is a very slightly scalene ellipsoid due to tidal stretching, with its long axis displaced 30° from facing the Earth, due to gravitational anomalies from impact basins. Its shape is more elongated than current tidal forces can account for. This 'fossil bulge' indicates that the Moon solidified when it orbited at half its current distance to the Earth, and that it is now too cold for its shape to restore hydrostatic equilibrium at its current orbital distance.

Size and mass

The Moon is by size and mass the fifth largest natural satellite of the Solar System, categorizeable as one of its planetary-mass moons, making it a satellite planet under the geophysical definitions of the term. It is smaller than Mercury and considerably larger than the largest dwarf planet of the Solar System, Pluto. While the minor-planet moon Charon of the Pluto-Charon system is larger relative to Pluto, the Moon is the largest natural satellite of the Solar System relative to their primary planets.

The Moon's diameter is about 3,500 km, more than a quarter of Earth's, with the face of the Moon comparable to the width of either Australia, Europe or the US without Alaska. The whole surface area of the Moon is about 38 million square kilometers, between the size of the Americas ( North and South America) and Africa.

The Moon's mass is 1/81 of Earth's, being the second densest among the planetary moons, and having the second highest surface gravity, after Io, at and an escape velocity of 2.38 km/s .

Moon's internal structure: solid inner core (iron-metallic), molten outer core, hardened mantle and crust. The crust on the Moon's near side permanently facing Earth is thinner, featuring larger areas flooded by material of the once molten mantle forming today's lunar mare.

The Moon is a differentiated body that was initially in hydrostatic equilibrium but has since departed from this condition. It has a geochemically distinct crust, mantle, and core. The Moon has a solid iron-rich inner core with a radius possibly as small as 240 kilometres (150 mi) and a fluid outer core primarily made of liquid iron with a radius of roughly 300 kilometres (190 mi). Around the core is a partially molten boundary layer with a radius of about 500 kilometres (310 mi). This structure is thought to have developed through the fractional crystallization of a global magma ocean shortly after the Moon's formation 4.5 billion years ago.

Crystallization of this magma ocean would have created a mafic mantle from the precipitation and sinking of the minerals olivine, clinopyroxene, and orthopyroxene; after about three-quarters of the magma ocean had crystallized, lower-density plagioclase minerals could form and float into a crust atop. The final liquids to crystallize would have been initially sandwiched between the crust and mantle, with a high abundance of incompatible and heat-producing elements. Consistent with this perspective, geochemical mapping made from orbit suggests a crust of mostly anorthosite. The Moon rock samples of the flood lavas that erupted onto the surface from partial melting in the mantle confirm the mafic mantle composition, which is more iron-rich than that of Earth. The crust is on average about 50 kilometres (31 mi) thick.

The Moon is the second-densest satellite in the Solar System, after Io. However, the inner core of the Moon is small, with a radius of about 350 kilometres (220 mi) or less, around 20% of the radius of the Moon. Its composition is not well understood, but is probably metallic iron alloyed with a small amount of sulfur and nickel; analyses of the Moon's time-variable rotation suggest that it is at least partly molten. The pressure at the lunar core is estimated to be 5 GPa (49,000 atm).

Gravitational field

An astronaut jumping on the Moon, illustrating that the gravitational pull of the Moon is approximately 1/6 of Earth's.

The Moon's gravitational field is not uniform. The details of the gravitational field have been measured through tracking the Doppler shift of radio signals emitted by orbiting spacecraft. The main lunar gravity features are mascons, large positive gravitational anomalies associated with some of the giant impact basins, partly caused by the dense mare basaltic lava flows that fill those basins. The anomalies greatly influence the orbit of spacecraft about the Moon. There are some puzzles: lava flows by themselves cannot explain all of the gravitational signature, and some mascons exist that are not linked to mare volcanism.

Magnetic field

The Moon has an external magnetic field of less than 0.2 nanoteslas, or less than one hundred thousandth that of Earth. The Moon does not currently have a global dipolar magnetic field and only has crustal magnetization likely acquired early in its history when a dynamo was still operating. However, early in its history, 4 billion years ago, its magnetic field strength was likely close to that of Earth today. This early dynamo field apparently expired by about one billion years ago, after the lunar core had completely crystallized. Theoretically, some of the remnant magnetization may originate from transient magnetic fields generated during large impacts through the expansion of plasma clouds. These clouds are generated during large impacts in an ambient magnetic field. This is supported by the location of the largest crustal magnetizations situated near the antipodes of the giant impact basins.

Atmosphere

The thin lunar atmosphere is visible on the Moon's surface at sunrise and sunset with the lunar horizon glow[84] and lunar twilight rays, like Earth's crepuscular rays. This Apollo 17 sketch depicts the glow and rays[85] among the general zodiacal light.[86]

The Moon has an atmosphere so tenuous as to be nearly vacuum, with a total mass of less than 10 tonnes (9.8 long tons; 11 short tons). The surface pressure of this small mass is around 3 × 10 −15 atm (0.3 nPa); it varies with the lunar day. Its sources include outgassing and sputtering, a product of the bombardment of lunar soil by solar wind ions. Elements that have been detected include sodium and potassium, produced by sputtering (also found in the atmospheres of Mercury and Io); helium-4 and neon from the solar wind; and argon-40, radon-222, and polonium-210, outgassed after their creation by radioactive decay within the crust and mantle. The absence of such neutral species (atoms or molecules) as oxygen, nitrogen, carbon, hydrogen and magnesium, which are present in the regolith, is not understood. Water vapor has been detected by Chandrayaan-1 and found to vary with latitude, with a maximum at ~60-70 degrees; it is possibly generated from the sublimation of water ice in the regolith. These gases either return into the regolith because of the Moon's gravity or are lost to space, either through solar radiation pressure or, if they are ionized, by being swept away by the solar wind's magnetic field.

Studies of Moon magma samples retrieved by the Apollo missions demonstrate that the Moon had once possessed a relatively thick atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions, was twice the thickness of that of present-day Mars. The ancient lunar atmosphere was eventually stripped away by solar winds and dissipated into space.

A permanent Moon dust cloud exists around the Moon, generated by small particles from comets. Estimates are 5 tons of comet particles strike the Moon's surface every 24 hours, resulting in the ejection of dust particles. The dust stays above the Moon approximately 10 minutes, taking 5 minutes to rise, and 5 minutes to fall. On average, 120 kilograms of dust are present above the Moon, rising up to 100 kilometers above the surface. Dust counts made by LADEE's Lunar Dust EXperiment (LDEX) found particle counts peaked during the Geminid, Quadrantid, Northern Taurid, and Omicron Centaurid meteor showers, when the Earth, and Moon pass through comet debris. The lunar dust cloud is asymmetric, being more dense near the boundary between the Moon's dayside and nightside.

Surface conditions

Gene Cernan with lunar dust stuck on his suit. Lunar dust is highly abrasive and can cause damage to human lungs, nervous, and cardiovascular systems.[96]

Ionizing radiation from cosmic rays, the Sun and the resulting neutron radiation produce radiation levels on average of 1.369 millisieverts per day during lunar daytime, which is about 2.6 times more than on the International Space Station with 0.53 millisieverts per day at about 400 km above Earth in orbit, 5-10 times more than during a trans-Atlantic flight, 200 times more than on Earth's surface. For further comparison radiation on a flight to Mars is about 1.84 millisieverts per day and on Mars on average 0.64 millisieverts per day, with some locations on Mars possibly having levels as low as 0.342 millisieverts per day.

The Moon's axial tilt with respect to the ecliptic is only 1.5427°, much less than the 23.44° of Earth. Because of this small tilt, the Moon's solar illumination varies much less with season than on Earth and it allows for the existence of some peaks of eternal light at the Moon's north pole, at the rim of the crater Peary.

The surface is exposed to drastic temperature differences ranging from 140 °C to −171 °C depending on the solar irradiance. Because of the lack of atmosphere, temperatures of different areas vary particularly upon whether they are in sunlight or shadow, making topographical details play a decisive role on local surface temperatures. Parts of many craters, particularly the bottoms of many polar craters, are permanently shadowed, these " craters of eternal darkness" have extremely low temperatures. The Lunar Reconnaissance Orbiter measured the lowest summer temperatures in craters at the southern pole at 35 K (−238 °C; −397 °F) and just 26 K (−247 °C; −413 °F) close to the winter solstice in the north polar crater Hermite. This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of Pluto.

Blanketed on top of the Moon's crust is a highly comminuted (broken into ever smaller particles) and impact gardened mostly gray surface layer called regolith, formed by impact processes. The finer regolith, the lunar soil of silicon dioxide glass, has a texture resembling snow and a scent resembling spent gunpowder. The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from 10-15 m (33-49 ft) in the highlands and 4-5 m (13-16 ft) in the maria. Beneath the finely comminuted regolith layer is the megaregolith, a layer of highly fractured bedrock many kilometers thick.

These extreme conditions for example are considered to make it unlikely for spacecraft to harbor bacterial spores at the Moon longer than just one lunar orbit.

Surface features

The topography of the Moon has been measured with laser altimetry and stereo image analysis. Its most extensive topographic feature is the giant far-side South Pole-Aitken basin, some 2,240 km (1,390 mi) in diameter, the largest crater on the Moon and the second-largest confirmed impact crater in the Solar System. At 13 km (8.1 mi) deep, its floor is the lowest point on the surface of the Moon. The highest elevations of the Moon's surface are located directly to the northeast, which might have been thickened by the oblique formation impact of the South Pole-Aitken basin. Other large impact basins such as Imbrium, Serenitatis, Crisium, Smythii, and Orientale possess regionally low elevations and elevated rims. The far side of the lunar surface is on average about 1.9 km (1.2 mi) higher than that of the near side.

The discovery of fault scarp cliffs suggest that the Moon has shrunk by about 90 metres (300 ft) within the past billion years. Similar shrinkage features exist on Mercury. Mare Frigoris, a basin near the north pole long assumed to be geologically dead, has cracked and shifted. Since the Moon does not have tectonic plates, its tectonic activity is slow and cracks develop as it loses heat.

Volcanic features

The main features visible from Earth by the naked eye are dark and relatively featureless lunar plains called (singular mare; Latin for "seas", as they were once believed to be filled with water) are vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water. The majority of these lava deposits erupted or flowed into the depressions associated with impact basins. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side "maria".

Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side compared with 2% of the far side. This is likely due to a concentration of heat-producing elements under the crust on the near side, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt. Most of the Moon's mare basalts erupted during the Imbrian period, 3.3-3.7 billion years ago, though some being as young as 1.2 billion years and as old as 4.2 billion years.

Old hardened lava flows of Mare Imbrium forming wrinkle ridges

In 2006, a study of Ina, a tiny depression in Lacus Felicitatis, found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old. Moonquakes and releases of gas indicate continued lunar activity. Evidence of recent lunar volcanism has been identified at 70 irregular mare patches, some less than 50 million years old. This raises the possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements. Evidence has been found for 2-10 million years old basaltic volcanism within the crater Lowell, inside the Orientale basin. Some combination of an initially hotter mantle and local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities on the far side in the Orientale basin.

The lighter-colored regions of the Moon are called terrae, or more commonly highlands, because they are higher than most maria. They have been radiometrically dated to having formed 4.4 billion years ago, and may represent plagioclase cumulates of the lunar magma ocean. In contrast to Earth, no major lunar mountains are believed to have formed as a result of tectonic events.

The concentration of maria on the near side likely reflects the substantially thicker crust of the highlands of the Far Side, which may have formed in a slow-velocity impact of a second moon of Earth a few tens of millions of years after the Moon's formation. Alternatively, it may be a consequence of asymmetrical tidal heating when the Moon was much closer to the Earth.

Impact craters

A major geologic process that has affected the Moon's surface is impact cratering, with craters formed when asteroids and comets collide with the lunar surface. There are estimated to be roughly 300,000 craters wider than 1 km (0.6 mi) on the Moon's near side. The lunar geologic timescale is based on the most prominent impact events, including Nectaris, Imbrium, and Orientale; structures characterized by multiple rings of uplifted material, between hundreds and thousands of kilometers in diameter and associated with a broad apron of ejecta deposits that form a regional stratigraphic horizon. The lack of an atmosphere, weather, and recent geological processes mean that many of these craters are well-preserved. Although only a few multi-ring basins have been definitively dated, they are useful for assigning relative ages. Because impact craters accumulate at a nearly constant rate, counting the number of craters per unit area can be used to estimate the age of the surface. The radiometric ages of impact-melted rocks collected during the Apollo missions cluster between 3.8 and 4.1 billion years old: this has been used to propose a Late Heavy Bombardment period of increased impacts.

High-resolution images from the Lunar Reconnaissance Orbiter in the 2010s show a contemporary crater-production rate significantly higher than was previously estimated. A secondary cratering process caused by distal ejecta is thought to churn the top two centimeters of regolith on a timescale of 81,000 years. This rate is 100 times faster than the rate computed from models based solely on direct micrometeorite impacts.

Lunar swirls

Wide angle image of a lunar swirl, the 70 kilometer long Reiner Gamma

Lunar swirls are enigmatic features found across the Moon's surface. They are characterized by a high albedo, appear optically immature (i.e. the optical characteristics of a relatively young regolith), and often have a sinuous shape. Their shape is often accentuated by low albedo regions that wind between the bright swirls. They are located in places with enhanced surface magnetic fields and many are located at the antipodal point of major impacts. Well known swirls include the Reiner Gamma feature and Mare Ingenii. They are hypothesized to be areas that have been partially shielded from the solar wind, resulting in slower space weathering.

Presence of water

Liquid water cannot persist on the lunar surface. When exposed to solar radiation, water quickly decomposes through a process known as photodissociation and is lost to space. However, since the 1960s, scientists have hypothesized that water ice may be deposited by impacting comets or possibly produced by the reaction of oxygen-rich lunar rocks, and hydrogen from solar wind, leaving traces of water which could possibly persist in cold, permanently shadowed craters at either pole on the Moon. Computer simulations suggest that up to 14,000 km ² (5,400 sq mi) of the surface may be in permanent shadow. The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation as a cost-effective plan; the alternative of transporting water from Earth would be prohibitively expensive.

In years since, signatures of water have been found to exist on the lunar surface. In 1994, the bistatic radar experiment located on the Clementine spacecraft, indicated the existence of small, frozen pockets of water close to the surface. However, later radar observations by Arecibo, suggest these findings may rather be rocks ejected from young impact craters. In 1998, the neutron spectrometer on the Lunar Prospector spacecraft showed that high concentrations of hydrogen are present in the first meter of depth in the regolith near the polar regions. Volcanic lava beads, brought back to Earth aboard Apollo 15, showed small amounts of water in their interior.

In 2008, NASA's Moon Mineralogy Mapper equipment on India's Chandrayaan-1 discovered, for the first time, water-rich minerals (shown in blue around a small crater from which they were ejected).

The 2008 Chandrayaan-1 spacecraft has since confirmed the existence of surface water ice, using the on-board Moon Mineralogy Mapper. The spectrometer observed absorption lines common to hydroxyl, in reflected sunlight, providing evidence of large quantities of water ice, on the lunar surface. The spacecraft showed that concentrations may possibly be as high as 1,000 ppm. Using the mapper's reflectance spectra, indirect lighting of areas in shadow confirmed water ice within 20° latitude of both poles in 2018. In 2009, sent a 2,300 kg (5,100 lb) impactor into a permanently shadowed polar crater, and detected at least 100 kg (220 lb) of water in a plume of ejected material. Another examination of the LCROSS data showed the amount of detected water to be closer to 155 ± 12 kg (342 ± 26 lb).

In May 2011, 615-1410 ppm water in melt inclusions in lunar sample 74220 was reported, the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17 mission in 1972. The inclusions were formed during explosive eruptions on the Moon approximately 3.7 billion years ago. This concentration is comparable with that of magma in Earth's upper mantle. Although of considerable selenological interest, this insight does not mean that water is easily available since the sample originated many kilometers below the surface, and the inclusions are so difficult to access that it took 39 years to find them with a state-of-the-art ion microprobe instrument.

Analysis of the findings of the Moon Mineralogy Mapper (M3) revealed in August 2018 for the first time "definitive evidence" for water-ice on the lunar surface. The data revealed the distinct reflective signatures of water-ice, as opposed to dust and other reflective substances. The ice deposits were found on the North and South poles, although it is more abundant in the South, where water is trapped in permanently shadowed craters and crevices, allowing it to persist as ice on the surface since they are shielded from the sun.

In October 2020, astronomers reported detecting molecular water on the sunlit surface of the Moon by several independent spacecraft, including the Stratospheric Observatory for Infrared Astronomy (SOFIA).

Earth-Moon system

The Earth and the Moon form the Earth-Moon satellite system with a shared center of mass, or barycenter. This barycenter is 1,700 km (1,100 mi) (about a quarter of Earth's radius) beneath the Earth's surface.

The Moon's orbit is slightly elliptical, with an orbital eccentricity of 0.055. The semi-major axis of the geocentric lunar orbit, called the Lunar distance, is approximately 400,000 km (250,000 miles or 1.28 light-seconds).

The Moon makes a complete orbit around Earth with respect to the fixed stars, its sidereal period, about once every 27.3 days. However, because the Earth-Moon system moves at the same time in its orbit around the Sun, it takes slightly longer, 29.5 days, to return at the same lunar phase, completing a full cycle, as seen from Earth. This synodic period or synodic month is commonly known as the lunar month and is equal to the length of the solar day on the Moon.

Due to tidal locking, the Moon has a 1:1 spin-orbit resonance. This rotation- orbit ratio makes the Moon's orbital periods around Earth equal to its corresponding rotation periods. This is the reason for only one side of the Moon, its so-called near side, being visible from Earth. That said, while the movement of the Moon is in resonance, it still is not without nuances such as libration, resulting in slightly changing perspectives, making over time and location on Earth about 59% of the Moon's surface visible from Earth.

Unlike most satellites of other planets, the Moon's orbital plane is closer to the ecliptic plane than to the planet's equatorial plane. The Moon's orbit is subtly perturbed by the Sun and Earth in many small, complex and interacting ways. For example, the plane of the Moon's orbit gradually rotates once every 18.61years, which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini's laws.

Minimum, mean and maximum distances of the Moon from Earth with its angular diameter as seen from Earth's surface, to scale

Tidal effects

Simplified diagram of the Moon's gravity tidal effect on the Earth

The gravitational attraction that Earth and the Moon (as well as the Sun) exert on each other manifests in a slightly greater attraction on the sides closest to each other, resulting in tidal forces. Ocean tides are the most widely experienced result of this, but tidal forces also considerably affect other mechanics of Earth, as well as the Moon and their system.

The lunar solid crust experiences tides of around 10 cm (4 in) amplitude over 27 days, with three components: a fixed one due to Earth, because they are in synchronous rotation, a variable tide due to orbital eccentricity and inclination, and a small varying component from the Sun. The Earth-induced variable component arises from changing distance and libration, a result of the Moon's orbital eccentricity and inclination (if the Moon's orbit were perfectly circular and un-inclined, there would only be solar tides). According to recent research, scientists suggest that the Moon's influence on the Earth may contribute to maintaining Earth's magnetic field.

The cumulative effects of stress built up by these tidal forces produces moonquakes. Moonquakes are much less common and weaker than are earthquakes, although moonquakes can last for up to an hour - significantly longer than terrestrial quakes - because of scattering of the seismic vibrations in the dry fragmented upper crust. The existence of moonquakes was an unexpected discovery from seismometers placed on the Moon by Apollo astronauts from 1969 through 1972.

The most commonly known effect of tidal forces are elevated sea levels called ocean tides. While the Moon exerts most of the tidal forces, the Sun also exerts tidal forces and therefore contributes to the tides as much as 40% of the Moon's tidal force; producing in interplay the spring and neap tides.

The tides are two bulges in the Earth's oceans, one on the side facing the Moon and the other on the side opposite. As the Earth rotates on its axis, one of the ocean bulges (high tide) is held in place "under" the Moon, while another such tide is opposite. As a result, there are two high tides, and two low tides in about 24 hours. Since the Moon is orbiting the Earth in the same direction of the Earth's rotation, the high tides occur about every 12 hours and 25 minutes; the 25 minutes is due to the Moon's time to orbit the Earth.

If the Earth were a water world (one with no continents) it would produce a tide of only one meter, and that tide would be very predictable, but the ocean tides are greatly modified by other effects:

the frictional coupling of water to Earth's rotation through the ocean floors

the inertia of water's movement

ocean basins that grow shallower near land

the sloshing of water between different ocean basins

As a result, the timing of the tides at most points on the Earth is a product of observations that are explained, incidentally, by theory.

Delays in the tidal peaks of both ocean and solid-body tides cause torque in opposition to the Earth's rotation. This "drains" angular momentum and rotational kinetic energy from Earth's rotation, slowing the Earth's rotation. That angular momentum, lost from the Earth, is transferred to the Moon in a process known as tidal acceleration, which lifts the Moon into a higher orbit while lowering orbital speed around the Earth.

Thus the distance between Earth and Moon is increasing, and the Earth's rotation is slowing in reaction. Measurements from laser reflectors left during the Apollo missions ( lunar ranging experiments) have found that the Moon's distance increases by 38 mm (1.5 in) per year (roughly the rate at which human fingernails grow). Atomic clocks show that Earth's day lengthens by about 17 microseconds every year, slowly increasing the rate at which UTC is adjusted by leap seconds.

This tidal drag makes the rotation of the Earth and the orbital period of the Moon very slowly match. This matching first results in tidally locking the lighter body of the orbital system, as is already the case with the Moon. Theoretically, in 50 billion years, the Earth's rotation will have slowed to the point of matching the Moon's orbital period, causing the Earth to always present the same side to the Moon. However, the Sun will become a red giant, engulfing the Earth-Moon system, long before then.

Position and appearance

The Moon's highest altitude at culmination varies by its lunar phase, or more correctly its orbital position, and time of the year, or more correctly the position of the Earth's axis. The full moon is highest in the sky during winter and lowest during summer (for each hemisphere respectively), with its altitude changing towards dark moon to the opposite.

At the North and South Poles the Moon is 24 hours above the horizon for two weeks every tropical month (about 27.3 days), comparable to the polar day of the tropical year. Zooplankton in the Arctic use moonlight when the Sun is below the horizon for months on end.

The apparent orientation of the Moon depends on its position in the sky and the hemisphere of the Earth from which it is being viewed. In the northern hemisphere it appears upside down compared to the view from the southern hemisphere. Sometimes the "horns" of a crescent moon appear to be pointing more upwards than sideways. This phenomenon is called a wet moon and occurs more frequently in the tropics.

The distance between the Moon and Earth varies from around 356,400 km (221,500 mi) ( perigee) to 406,700 km (252,700 mi) (apogee), making the Moon's apparent size fluctuate. On average the Moon's angular diameter is about 0.52°, roughly the same apparent size as the Sun (see § Eclipses). In addition, a purely psychological effect, known as the Moon illusion, makes the Moon appear larger when close to the horizon.

Despite the Moon's tidal locking, the effect of libration makes about 59% of the Moon's surface visible from Earth over the course of one month.

Comparison between the Moon on the left, rotating tidally locked (correct), and with the Moon on the right, without rotation (incorrect)

The tidally locked synchronous rotation of the Moon as it orbits the Earth results in it always keeping nearly the same face turned towards the planet. The side of the Moon that faces Earth is called the near side, and the opposite the far side. The far side is often inaccurately called the "dark side", but it is in fact illuminated as often as the near side: once every 29.5 Earth days. During dark moon to new moon, the near side is dark.

The Moon originally rotated at a faster rate, but early in its history its rotation slowed and became tidally locked in this orientation as a result of frictional effects associated with tidal deformations caused by Earth. With time, the energy of rotation of the Moon on its axis was dissipated as heat, until there was no rotation of the Moon relative to Earth. In 2016, planetary scientists using data collected on the 1998-99 NASA Lunar Prospector mission, found two hydrogen-rich areas (most likely former water ice) on opposite sides of the Moon. It is speculated that these patches were the poles of the Moon billions of years ago before it was tidally locked to Earth.

Illumination and phases

Half of the Moon's surface is always illuminated by the Sun (except during a lunar eclipse). Earth also reflects light onto the Moon, observable at times as Earthlight when it is again reflected back to Earth from areas of the near side of the Moon that are not illuminated by the Sun.

Since the Moon's axial tilt with respect to the ecliptic is 1.5427°, in every draconic year (346.62 days) the Sun moves from being 1.5427° north of the lunar equator to being 1.5427° south of it and then back, just as on Earth the Sun moves from the Tropic of Cancer to the Tropic of Capricorn and back once every tropical year. The poles of the Moon are therefore in the dark for half a draconic year (or with only part of the Sun visible) and then lit for half a draconic year. The amount of sunlight falling on horizontal areas near the poles depends on the altitude angle of the Sun. But these "seasons" have little effect in more equatorial areas.

With the different positions of the Moon, different areas of it are illuminated by the Sun. This illumination of different lunar areas, as viewed from Earth, produces the different lunar phases during the synodic month. A phase is equal to the area of the visible lunar sphere that is illuminated by the Sun. This area or degree of illumination is given by , where is the elongation (i.e., the angle between Moon, the observer on Earth, and the Sun).

The monthly changes in the angle between the direction of sunlight and view from Earth, and the phases of the Moon that result, as viewed from the Northern Hemisphere. The Earth-Moon distance is not to scale.

On 14 November 2016, the Moon was at full phase closer to Earth than it had been since 1948. It was 14% closer and larger than its farthest position in apogee. This closest point coincided within an hour of a full moon, and it was 30% more luminous than when at its greatest distance because of its increased apparent diameter, which made it a particularly notable example of a " supermoon".

At lower levels, the human perception of reduced brightness as a percentage is provided by the following formula:

When the actual reduction is 1.00 / 1.30, or about 0.770, the perceived reduction is about 0.877, or 1.00 / 1.14. This gives a maximum perceived increase of 14% between apogee and perigee moons of the same phase.

There has been historical controversy over whether observed features on the Moon's surface change over time. Today, many of these claims are thought to be illusory, resulting from observation under different lighting conditions, poor astronomical seeing, or inadequate drawings. However, outgassing does occasionally occur and could be responsible for a minor percentage of the reported lunar transient phenomena. Recently, it has been suggested that a roughly 3 km (1.9 mi) diameter region of the lunar surface was modified by a gas release event about a million years ago.

Albedo and color

The changing apparent color of the Moon, filtered by Earth's atmosphere

The Moon has an exceptionally low albedo, giving it a reflectance that is slightly brighter than that of worn asphalt. Despite this, it is the brightest object in the sky after the Sun. This is due partly to the brightness enhancement of the opposition surge; the Moon at quarter phase is only one-tenth as bright, rather than half as bright, as at full moon. Additionally, color constancy in the visual system recalibrates the relations between the colors of an object and its surroundings, and because the surrounding sky is comparatively dark, the sunlit Moon is perceived as a bright object. The edges of the full moon seem as bright as the center, without limb darkening, because of the reflective properties of lunar soil, which retroreflects light more towards the Sun than in other directions. The Moon's color depends on the light the Moon reflects, which in turn depends on the Moon's surface and its features, having for example large darker regions. In general the lunar surface reflects a brown-tinged gray light.

Viewed from Earth the air filters the reflected light, at times giving it a red color depending on the angle of the Moon in the sky and thickness of the atmosphere, or a blue tinge depending on the particles in the air, as in cases of volcanic particles. The terms blood moon and blue moon do not necessarily refer to circumstances of red or blue moonlight, but are rather particular cultural references such as particular full moons of a year.

Eclipses only occur when the Sun, Earth, and Moon are all in a straight line (termed " syzygy"). Solar eclipses occur at new moon, when the Moon is between the Sun and Earth. In contrast, lunar eclipses occur at full moon, when Earth is between the Sun and Moon. The apparent size of the Moon is roughly the same as that of the Sun, with both being viewed at close to one-half a degree wide. The Sun is much larger than the Moon but it is the vastly greater distance that gives it the same apparent size as the much closer and much smaller Moon from the perspective of Earth. The variations in apparent size, due to the non-circular orbits, are nearly the same as well, though occurring in different cycles. This makes possible both total (with the Moon appearing larger than the Sun) and annular (with the Moon appearing smaller than the Sun) solar eclipses. In a total eclipse, the Moon completely covers the disc of the Sun and the solar corona becomes visible to the naked eye. Because the distance between the Moon and Earth is very slowly increasing over time, the angular diameter of the Moon is decreasing. As it evolves toward becoming a red giant, the size of the Sun, and its apparent diameter in the sky, are slowly increasing. The combination of these two changes means that hundreds of millions of years ago, the Moon would always completely cover the Sun on solar eclipses, and no annular eclipses were possible. Likewise, hundreds of millions of years in the future, the Moon will no longer cover the Sun completely, and total solar eclipses will not occur.

Because the Moon's orbit around Earth is inclined by about 5.145° (5° 9') to the orbit of Earth around the Sun, eclipses do not occur at every full and new moon. For an eclipse to occur, the Moon must be near the intersection of the two orbital planes. The periodicity and recurrence of eclipses of the Sun by the Moon, and of the Moon by Earth, is described by the saros, which has a period of approximately 18 years.

Because the Moon continuously blocks the view of a half-degree-wide circular area of the sky, the related phenomenon of occultation occurs when a bright star or planet passes behind the Moon and is occulted: hidden from view. In this way, a solar eclipse is an occultation of the Sun. Because the Moon is comparatively close to Earth, occultations of individual stars are not visible everywhere on the planet, nor at the same time. Because of the precession of the lunar orbit, each year different stars are occulted.

History of exploration and human presence

Pre-telescopic observation (before 1609)

It is believed by some that 20-30,000 year old tally sticks were used to observe the phases of the Moon, keeping time using the waxing and waning of the Moon's phases. One of the earliest-discovered possible depictions of the Moon is a 5000-year-old rock carvingOrthostat 47 at Knowth, Ireland.

The ( ancient Greek philosopher Anaxagoras () reasoned that the Sun and Moon were both giant spherical rocks, and that the latter reflected the light of the former. Elsewhere in the 5th century BC to 4th century BC, Babylonian astronomers had recorded the 18-year Saros cycle of lunar eclipses, and Indian astronomers had described the Moon's monthly elongation. The Chinese astronomer Shi Shen fl. 4th century BC) gave instructions for predicting solar and lunar eclipses.

In Aristotle's (384-322 BC) description of the universe, the Moon marked the boundary between the spheres of the mutable elements (earth, water, air and fire), and the imperishable stars of aether, an influential philosophy that would dominate for centuries. Archimedes (287-212 BC) designed a planetarium that could calculate the motions of the Moon and other objects in the Solar System. In the 2nd century BC, Seleucus of Seleucia correctly theorized that tides were due to the attraction of the Moon, and that their height depends on the Moon's position relative to the Sun. In the same century, Aristarchus computed the size and distance of the Moon from Earth, obtaining a value of about twenty times the radius of Earth for the distance.

Although the Chinese of the Han Dynasty believed the Moon to be energy equated to , their 'radiating influence' theory recognized that the light of the Moon was merely a reflection of the Sun, and Jing Fang (78-37 BC) noted the sphericity of the Moon. Ptolemy (90-168 AD) greatly improved on the numbers of Aristarchus, calculating a mean distance of 59 times Earth's radius and a diameter of 0.292 Earth diameters, close to the correct values of about 60 and 0.273 respectively. In the 2nd century AD, Lucian wrote the novel A True Story, in which the heroes travel to the Moon and meet its inhabitants. In 499 AD, the Indian astronomer Aryabhata mentioned in his Aryabhatiya that reflected sunlight is the cause of the shining of the Moon. The astronomer and physicist Alhazen (965-1039) found that sunlight was not reflected from the Moon like a mirror, but that light was emitted from every part of the Moon's sunlit surface in all directions. Shen Kuo (1031-1095) of the Song dynasty created an allegory equating the waxing and waning of the Moon to a round ball of reflective silver that, when doused with white powder and viewed from the side, would appear to be a crescent.

During the Middle Ages, before the invention of the telescope, the Moon was increasingly recognised as a sphere, though many believed that it was "perfectly smooth".

Telescopic exploration (1609-1959)

Galileo's sketches of the Moon from the ground-breaking Sidereus Nuncius (1610), publishing among other findings the first descriptions of the Moons topography

In 1609, Galileo Galilei used an early telescope to make drawings of the Moon for his book Sidereus Nuncius, and deduced that it was not smooth but had mountains and craters. Thomas Harriot had made, but not published such drawings a few months earlier.

Telescopic mapping of the Moon followed: later in the 17th century, the efforts of Giovanni Battista Riccioli and Francesco Maria Grimaldi led to the system of naming of lunar features in use today. The more exact 1834-1836 Mappa Selenographica of Wilhelm Beer and Johann Heinrich Mädler, and their associated 1837 book Der Mond, the first trigonometrically accurate study of lunar features, included the heights of more than a thousand mountains, and introduced the study of the Moon at accuracies possible in earthly geography. Lunar craters, first noted by Galileo, were thought to be volcanic until the 1870s proposal of Richard Proctor that they were formed by collisions. This view gained support in 1892 from the experimentation of geologist Grove Karl Gilbert, and from comparative studies from 1920 to the 1940s, leading to the development of lunar stratigraphy, which by the 1950s was becoming a new and growing branch of astrogeology.

First missions to the Moon (1959-1990)

After World War II the first launch systems were developed and by the end of the 1950s they reached capabilities that allowed the Soviet Union and the United States to launch spacecraft into space. The Cold War fueled a closely followed development of launch systems by the two states, resulting in the so-called Space Race and its later phase the Moon Race, accelerating efforts and interest in exploration of the Moon.

First view of the far side of the Moon, taken by Luna 3, 7 October 1959. Clearly visible is Mare Moscoviense (top right) and a mare triplet of Mare Crisium, Mare Marginis and Mare Smythii (left center).

After the first spaceflight of Sputnik 1 in 1957 during International Geophysical Year the spacecraft of the Soviet Union's Luna program were the first to accomplish a number of goals. Following three unnamed failed missions in 1958, the first human-made object escaped Earth's gravity and passed near the Moon in 1959. Later that year the first human-made object reached the Moon's surface by intentionally impacting. By the end of the year reached as the first human-made object the normally occluded far side of the Moon, taking the first photographs of it. The first spacecraft to perform a successful lunar soft landing was and the first vehicle to orbit the Moon was , both in 1966.

Earthrise, the first color image of Earth taken by a human from the Moon, during Apollo 8 (1968) the first time a crewed spacecraft left Earth orbit and reached another astronomical body

Following President John F. Kennedy's 1961 commitment to a crewed Moon landing before the end of the decade, the United States, under NASA leadership, launched a series of uncrewed probes to develop an understanding of the lunar surface in preparation for human missions: the Jet Propulsion Laboratory's Ranger program, the Lunar Orbiter program and the Surveyor program. The crewed Apollo program was developed in parallel; after a series of uncrewed and crewed tests of the Apollo spacecraft in Earth orbit, and spurred on by a potential Soviet lunar human landing, in 1968 Apollo 8 made the first human mission to lunar orbit (the first Earthlings, two tortoises, had circled the Moon three months earlier on the Soviet Union's Zond 5, followed by turtles on Zond 6). The subsequent landing of the first humans on the Moon in 1969 is seen by many as the culmination of the Space Race.

Neil Armstrong became the first person to walk on the Moon as the commander of the American mission Apollo 11 by first setting foot on the Moon at 02:56 UTC on 21 July 1969. An estimated 500 million people worldwide watched the transmission by the Apollo TV camera, the largest television audience for a live broadcast at that time. The Apollo missions 11 to 17 (except Apollo 13, which aborted its planned lunar landing) removed 380.05 kilograms (837.87 lb) of lunar rock and soil in 2,196 separate samples.

Scientific instrument packages were installed on the lunar surface during all the Apollo landings. Long-lived instrument stations, including heat flow probes, seismometers, and magnetometers, were installed at the Apollo 12, 14, 15, 16, and 17 landing sites. Direct transmission of data to Earth concluded in late 1977 because of budgetary considerations, but as the stations' lunar laser ranging corner-cube retroreflector arrays are passive instruments, they are still being used. Apollo 17 in 1972 remains the last crewed mission to the Moon. Explorer 49 in 1973 was the last dedicated U.S. probe to the Moon until the 1990s.

The Soviet Union continued sending robotic missions to the Moon until 1976, deploying in 1970 with Luna 17 the first remote controlled rover Lunokhod 1 on an extraterrestrial surface, and collecting and returning 0.3 kg of rock and soil samples with three Luna sample return missions ( in 1970, in 1972, and in 1976).

Moon Treaty and explorational absence (1976-1990)

A near lunar quietude of fourteen years followed the last Soviet mission to the Moon of 1976. Astronautics had shifted its focus towards the exploration of the inner (e.g. Venera program) and outer (e.g. Pioneer 10, 1972) Solar System planets, but also towards Earth orbit, developing and continuously operating, beside communication satellites, Earth observation satellites (e.g. Landsat program, 1972), space telescopes and particularly space stations (e.g. Salyut program, 1971).

The until 1979 negotiated Moon treaty, with its ratification in 1984 by its few signatories was about the only major activity regarding the Moon until 1990.

Renewed exploration (1990-present)

Map of all soft landing sites on the near side of the Moon (2020)

In 1990 - Hagoromo, the first dedicated lunar mission since 1976, reached the Moon. Sent by Japan, it became the first mission that was not a Soviet Union or U.S. mission to the Moon.

In 1994, the U.S. dedicated a mission to fly a spacecraft (Clementine) to the Moon again for the first time since 1973. This mission obtained the first near-global topographic map of the Moon, and the first global multispectral images of the lunar surface. In 1998, this was followed by the Lunar Prospector mission, whose instruments indicated the presence of excess hydrogen at the lunar poles, which is likely to have been caused by the presence of water ice in the upper few meters of the regolith within permanently shadowed craters.

The next years saw a row of first missions to the Moon by a new group of states actively exploring the Moon. Between 2004 and 2006 the first spacecraft by the European Space Agency (ESA) () reached the Moon, recording the first detailed survey of chemical elements on the lunar surface. The Chinese Lunar Exploration Program began with between 2007 and 2009, obtaining a full image map of the Moon. India reached the Moon in 2008 for the first time with its Chandrayaan-1, creating a high-resolution chemical, mineralogical and photo-geological map of the lunar surface, and confirming the presence of water molecules in lunar soil.

The U.S. launched the Lunar Reconnaissance Orbiter (LRO) and the impactor on 18 June 2009. LCROSS completed its mission by making a planned and widely observed impact in the crater Cabeus on 9 October 2009, whereas LRO is currently in operation, obtaining precise lunar altimetry and high-resolution imagery.

China continued its lunar program in 2010 with , mapping the surface at a higher resolution over an eight-month period, and in 2013 with , a lunar lander along with a lunar rover named ( Chinese: 玉兔; 'Jade Rabbit'). This was the first lunar rover mission since in 1973 and the first lunar soft landing since in 1976.

In 2014 the first privately funded probe, the Manfred Memorial Moon Mission, reached the Moon.

Another Chinese rover mission, , achieved the first landing on the Moon's far side in early 2019.

Also in 2019, India successfully sent its second probe, Chandrayaan-2 to the Moon.

In 2020, China carried out its first robotic sample return mission (), bringing back 1,731 grams of lunar material to Earth.

With the signing of the U.S.-led Artemis Accords in 2020, the Artemis program aims to return the astronauts to the Moon in the 2020s. The Accords have been joined by a growing number of countries. The introduction of the Artemis Accords has fueled a renewed discussion about the international framework and cooperation of lunar activity, building on the Moon Treaty and the ESA-led Moon Village concept. The U.S. developed plans for returning to the Moon beginning in 2004, which resulted in several programs. The Artemis program has advanced the farthest, and includes plans to send the first woman to the Moon as well as build an international lunar space station called Lunar Gateway.

Upcoming lunar missions include the Artemis program missions and Russia's first lunar mission, : an uncrewed lander with a set of seismometers, and an orbiter based on its failed Martian Fobos-Grunt mission.

In 2021, China announced a plan with Russia to develop and construct an International Lunar Research Station in the 2030s.

Human presence

Humans last landed on the Moon during the Apollo Program, a series of crewed exploration missions carried out from 1969 to 1972. Lunar orbit has seen uninterrupted presence of orbiters since 2006, performing mainly lunar observation and providing relayed communication for robotic missions on the lunar surface.

Lunar orbits and orbits around Earth-Moon Lagrange points are used to establish a near-lunar infrastructure to enable increasing human activity in cislunar space as well as on the Moon's surface. Missions at the far side of the Moon or the lunar north and south polar regions need spacecraft with special orbits, such as the Queqiao relay satellite or the planned first extraterrestrial space station, the Lunar Gateway.

Human impact

Artifacts of human activity, Apollo 17's Lunar Surface Experiments Package[251]

While the Moon has the lowest planetary protection target-categorization, its degradation as a pristine body and scientific place has been discussed. If there is astronomy performed from the Moon, it will need to be free from any physical and radio pollution. While the Moon has no significant atmosphere, traffic and impacts on the Moon causes clouds of dust that can spread far and possibly contaminate the original state of the Moon and its special scientific content. Scholar Alice Gorman asserts that, although the Moon is inhospitable, it is not dead, and that sustainable human activity would require treating the Moon's ecology as a co-participant.

The so-called " Tardigrade affair" of the 2019 crashed Beresheet lander and its carrying of tardigrades has been discussed as an example for lacking measures and lacking international regulation for planetary protection.

Space debris beyond Earth around the Moon has been considered as a future challenge with increasing numbers of missions to the Moon, particularly as a danger for such missions. As such lunar waste management has been raised as an issue which future lunar missions, particularly on the surface, need to tackle.

Beside the remains of human activity on the Moon, there have been some intended permanent installations like the Moon Museum art piece, Apollo 11 goodwill messages, six lunar plaques, the Fallen Astronaut memorial, and other artifacts.

Longterm missions continuing to be active are some orbiters such as the 2009-launched Lunar Reconnaissance Orbiter surveilling the Moon for future missions, as well as some Landers such as the 2013-launched Chang'e 3 with its Lunar Ultraviolet Telescope still operational. Five retroreflectors have been installed on the Moon since the 1970s and since used for accurate measurements of the physical librations through laser ranging to the Moon.

There are several missions by different agencies and companies planned to establish a longterm human presence on the Moon, with the Lunar Gateway as the currently most advanced project as part of the Artemis program.

Astronomy from the Moon

The LCRT concept for a radio telescope on the Moon

The Moon is recognized as an excellent site for telescopes. It is relatively nearby; certain craters near the poles are permanently dark and cold and especially useful for infrared telescopes; and radio telescopes on the far side would be shielded from the radio chatter of Earth. The lunar soil, although it poses a problem for any moving parts of telescopes, can be mixed with carbon nanotubes and epoxies and employed in the construction of mirrors up to 50 meters in diameter. A lunar zenith telescope can be made cheaply with an ionic liquid.

In April 1972, the Apollo 16 mission recorded various astronomical photos and spectra in ultraviolet with the Far Ultraviolet Camera/Spectrograph.

The Moon has been also a site of Earth observation, particularly culturally as in the photograph called . The Earth appears in the Moon's sky with an apparent size of 1° 48′ to 2°, three to four times the size of the Moon or Sun in Earth's sky, or about the apparent width of two little fingers at an arm's length away.

Living on the Moon

Astronaut Buzz Aldrin in life-supporting suit looking back at the first lunar habitat and base, the Lunar Module Eagle of Tranquility Base, during Apollo 11 (1969), the first crewed Moon landing

The only instances of humans living on the Moon have taken place in an Apollo Lunar Module for several days at a time (for example, during the Apollo 17 mission). One challenge to astronauts during their stay on the surface is that lunar dust sticks to their suits and is carried into their quarters. Astronauts could taste and smell the dust, calling it the "Apollo aroma". This fine lunar dust can cause health issues.

In 2019, at least one plant seed sprouted in an experiment on the Chang'e 4 lander. It was carried from Earth along with other small life in its Lunar Micro Ecosystem.

Legal status

Although landers scattered pennants of the Soviet Union on the Moon, and U.S. flags were symbolically planted at their landing sites by the Apollo astronauts, no nation claims ownership of any part of the Moon's surface. Likewise no private ownership of parts of the Moon, or as a whole, is considered credible.

The 1967 Outer Space Treaty defines the Moon and all outer space as the " province of all mankind". It restricts the use of the Moon to peaceful purposes, explicitly banning military installations and weapons of mass destruction. A majority of countries are parties of this treaty. The 1979 Moon Agreement was created to elaborate, and restrict the exploitation of the Moon's resources by any single nation, leaving it to a yet unspecified international regulatory regime. As of January 2020, it has been signed and ratified by 18 nations, none of which have human spaceflight capabilities.

Since 2020, countries have joined the U.S. in their Artemis Accords, which are challenging the treaty. The U.S. has furthermore emphasized in a presidential executive order ("Encouraging International Support for the Recovery and Use of Space Resources.") that "the United States does not view outer space as a 'global commons'" and calls the Moon Agreement "a failed attempt at constraining free enterprise."

With Australia signing and ratifying both the Moon Treaty in 1986 as well as the Artemis Accords in 2020, there has been a discussion if they can be harmonized. In this light an Implementation Agreement for the Moon Treaty has been advocated for, as a way to compensate for the shortcomings of the Moon Treaty and to harmonize it with other laws and agreements such as the Artemis Accords, allowing it to be more widely accepted.

In the face of such increasing commercial and national interest, particularly prospecting territories, U.S. lawmakers have introduced in late 2020 specific regulation for the conservation of historic landing sites and interest groups have argued for making such sites World Heritage Sites and zones of scientific value protected zones, all of which add to the legal availability and territorialization of the Moon.

In 2021, the Declaration of the Rights of the Moon was created by a group of "lawyers, space archaeologists and concerned citizens", drawing on precedents in the Rights of Nature movement and the concept of legal personality for non-human entities in space.

Coordination

In light of future development on the Moon some international and multi- space agency organizations have been created:

In culture and life

The Venus of Laussel (c. 25,000 BP) holding a crescent shaped horn, the 13 notches on the horn may symbolize the number of days from menstruation to ovulation, or of menstrual cycles or moons per year.[285][286]

Since pre-historic times people have taken note of the Moon's phases, its waxing and waning, and used it to keep record of time. Tally sticks, notched bones dating as far back as 20-30,000 years ago, are believed by some to mark the phases of the Moon. The counting of the days between the Moon's phases gave eventually rise to generalized time periods of the full lunar cycle as months, and possibly of its phases as weeks.

The words for the month in a range of different languages carry this relation between the period of the month and the Moon etymologically. The English month as well as moon, and its cognates in other Indo-European languages (e.g. the Latin mensis and Ancient Greek ( meis) or (mēn), meaning "month") stem from the Proto-Indo-European (PIE) root of moon, *, derived from the PIE verbal root *-, "to measure", "indicat[ing] a functional conception of the Moon, i.e. marker of the month" ( cf. the English words measure and menstrual). To give another example from a different language family, the Chinese language uses the same word () for moon as well as for month, which furthermore can be found in the symbols for the word week ().

This lunar timekeeping gave rise to the historically dominant, but varied, lunisolar calendars. The 7th-century Islamic calendar is an example of a purely lunar calendar, where months are traditionally determined by the visual sighting of the hilal, or earliest crescent moon, over the horizon.

Of particular significance has been the occasion of full moon, highlighted and celebrated in a range of calendars and cultures. Around autumnal equinox, the Full Moon is called the Harvest Moon and is celebrated with festivities such as the Harvest Moon Festival of the Chinese Lunar Calendar, its second most important celebration after Chinese New Year.

Furthermore, association of time with the Moon can also be found in religion, such as the ancient Egyptian temporal and lunar deity Khonsu.

Cultural representation

Since prehistoric and ancient times humans have drawn the Moon and have described a range of understandings of it, having prominent importance in different cosmologies, often exhibiting a spirit, being a deity or an aspect, particularly in astrology.

For the representation of the Moon, especially its lunar phases, the crescent symbol (🌙) has been particularly used by many cultures. In writing systems such as Chinese the crescent has developed into the symbol , the word for Moon, and in ancient Egyptian it was the symbol 𓇹, which is spelled like the ancient Egyptian lunar deity , meaning Moon.

Iconographically the crescent was used in Mesopotamia as the primary symbol of Nanna/Sîn, the ancient Sumerian lunar deity, who was the father of Innana/Ishtar, the goddess of the planet Venus (symbolized as the eight pointed Star of Ishtar), and Utu/Shamash, the god of the Sun ( symbolized as a disc, optionally with eight rays), all three often depicted next to each other. Nanna was later known as Sîn, and was particularly associated with magic and sorcery.

The crescent was further used as an element of lunar deities wearing headgears or crowns in an arrangement reminiscent of horns, as in the case of the ancient Greek Selene or the ancient Egyptian Khonsu. Selene is associated with Artemis and paralleled by the Roman Luna, which both are occasionally depicted driving a chariot, like the Hindu lunar deity Chandra. The different or sharing aspects of deities within pantheons has been observed in many cultures, especially by later or contemporary culture, particularly forming triple deities. The Moon in Roman mythology for example has been associated with Juno and Diana, while Luna being identified as their byname and as part of a triplet ( diva triformis) with Diana and Proserpina, Hecate being identified as their binding manifestation as trimorphos.

The star and crescent (☪️) arrangement goes back to the Bronze Age, representing either the Sun and Moon, or the Moon and planet Venus, in combination. It came to represent the goddess Artemis or Hecate, and via the patronage of Hecate came to be used as a symbol of Byzantium, possibly influencing the development of the Ottoman flag, specifically the combination of the Turkish crescent with a star. Since then the heraldric use of the star and crescent proliferated becoming a popular symbol for Islam (as the of the Islamic calendar) and for a range of nations.

In Roman Catholic Marian veneration, the Virgin Mary ( Queen of Heaven) has been depicted since the late Middle Ages on a crescent and adorned with stars. In Islam Muhammad is particularly attributed with the Moon through the so-called splitting of the Moon ( Arabic: انشقاق القمر) miracle.

The contrast between the brighter highlands and the darker maria have been seen by different cultures forming abstract shapes, which are among others the Man in the Moon or the Moon Rabbit (e.g. the Chinese Tu'er Ye or in Indigenous American mythologies, as with the aspect of the Mayan Moon goddess).

In Western alchemy silver is associated with the Moon, and gold with the Sun.

Modern culture representation

The perception of the Moon in modern times has been informed by telescope enabled modern astronomy and later by spaceflight enabled actual human activity at the Moon, particularly the culturally impactful lunar landings. These new insights inspired cultural references, connecting romantic reflections about the Moon and speculative fiction such as science-fiction dealing with the Moon.

Contemporarily the Moon has been seen as a place for economic expansion into space, with missions prospecting for lunar resources. This has been accompanied with renewed public and critical reflection on humanity's cultural and legal relation to the celestial body, especially regarding colonialism, as in the 1970 poem " Whitey on the Moon". In this light the Moon's nature has been invoked, particularly for lunar conservation and as a common.

Lunar effect

The lunar effect is a purported unproven correlation between specific stages of the roughly 29.5-day lunar cycle and behavior and physiological changes in living beings on Earth, including humans. The Moon has long been associated with insanity and irrationality; the words lunacy and are derived from the Latin name for the Moon, Luna. Philosophers Aristotle and Pliny the Elder argued that the full moon induced insanity in susceptible individuals, believing that the brain, which is mostly water, must be affected by the Moon and its power over the tides, but the Moon's gravity is too slight to affect any single person. Even today, people who believe in a lunar effect claim that admissions to psychiatric hospitals, traffic accidents, homicides or suicides increase during a full moon, but dozens of studies invalidate these claims.

Explanatory notes

References

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The Moon is Earth's only natural satellite. It orbits at an average distance of (), about 30 times the planet's diameter. Being tidally locked, it always faces Earth with its near side. This results in the lunar month of 29.5 days matching the lunar day.

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A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the Sun. Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew.

In a primary rainbow, the arc shows red on the outer part and violet on the inner side. This rainbow is caused by light being refracted when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it.

In a double rainbow, a second arc is seen outside the primary arc, and has the order of its colours reversed, with red on the inner side of the arc. This is caused by the light being reflected twice on the inside of the droplet before leaving it.

Visibility

Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind the observer at a low altitude angle. Because of this, rainbows are usually seen in the western sky during the morning and in the eastern sky during the early evening. The most spectacular rainbow displays happen when half the sky is still dark with raining clouds and the observer is at a spot with clear sky in the direction of the Sun. The result is a luminous rainbow that contrasts with the darkened background. During such good visibility conditions, the larger but fainter secondary rainbow is often visible. It appears about 10° outside of the primary rainbow, with inverse order of colours.

The rainbow effect is also commonly seen near waterfalls or fountains. In addition, the effect can be artificially created by dispersing water droplets into the air during a sunny day. Rarely, a moonbow, lunar rainbow or nighttime rainbow, can be seen on strongly moonlit nights. As human visual perception for colour is poor in low light, moonbows are often perceived to be white.

It is difficult to photograph the complete semicircle of a rainbow in one frame, as this would require an angle of view of 84°. For a 35 mm camera, a wide-angle lens with a focal length of 19 mm or less would be required. Now that software for stitching several images into a panorama is available, images of the entire arc and even secondary arcs can be created fairly easily from a series of overlapping frames.

From above the Earth such as in an aeroplane, it is sometimes possible to see a rainbow as a full circle. This phenomenon can be confused with the glory phenomenon, but a glory is usually much smaller, covering only 5-20°.

The light of a primary rainbow arc is 96% polarised tangential to the arc. The light of the second arc is 90% polarised.

Number of colours in a spectrum or a rainbow

For colours seen by the human eye, the most commonly cited and remembered sequence is Isaac Newton's sevenfold red, orange, yellow, green, blue, indigo and violet, remembered by the mnemonic Richard Of York Gave Battle In Vain, or as the name of a fictional person ( Roy G. Biv). The initialism is sometimes referred to in reverse order, as VIBGYOR. More modernly, the rainbow is often divided into red, orange, yellow, green, cyan, blue and violet. The apparent discreteness of main colours is an artefact of human perception and the exact number of main colours is a somewhat arbitrary choice.

Newton, who admitted his eyes were not very critical in distinguishing colours, originally (1672) divided the spectrum into five main colours: red, yellow, green, blue and violet. Later he included orange and indigo, giving seven main colours by analogy to the number of notes in a musical scale. Newton chose to divide the visible spectrum into seven colours out of a belief derived from the beliefs of the ancient Greek sophists, who thought there was a connection between the colours, the musical notes, the known objects in the Solar System, and the days of the week. Scholars have noted that what Newton regarded at the time as "blue" would today be regarded as cyan, and what Newton called "indigo" would today be considered blue.

The colour pattern of a rainbow is different from a spectrum, and the colours are less saturated. There is spectral smearing in a rainbow since, for any particular wavelength, there is a distribution of exit angles, rather than a single unvarying angle. In addition, a rainbow is a blurred version of the bow obtained from a point source, because the disk diameter of the sun (0.533°) cannot be neglected compared to the width of a rainbow (2.36°). Further red of the first supplementary rainbow overlaps the violet of the primary rainbow, so rather than the final colour being a variant of spectral violet, it is actually a purple. The number of colour bands of a rainbow may therefore be different from the number of bands in a spectrum, especially if the droplets are particularly large or small. Therefore, the number of colours of a rainbow is variable. If, however, the word rainbow is used inaccurately to mean spectrum, it is the number of main colours in the spectrum.

Moreover, rainbows have bands beyond red and violet in the respective near infrared and ultraviolet regions, however, these bands are not visible to humans. Only near frequencies of these regions to the visible spectrum are included in rainbows, since water and air become increasingly opaque to these frequencies, scattering the light. The UV band is sometimes visible to cameras using black and white film.

The question of whether everyone sees seven colours in a rainbow is related to the idea of linguistic relativity. Suggestions have been made that there is universality in the way that a rainbow is perceived. However, more recent research suggests that the number of distinct colours observed and what these are called depend on the language that one uses, with people whose language has fewer colour words seeing fewer discrete colour bands.

Explanation

When sunlight encounters a raindrop, part of the light is reflected and the rest enters the raindrop. The light is refracted at the surface of the raindrop. When this light hits the back of the raindrop, some of it is reflected off the back. When the internally reflected light reaches the surface again, once more some is internally reflected and some is refracted as it exits the drop. (The light that reflects off the drop, exits from the back, or continues to bounce around inside the drop after the second encounter with the surface, is not relevant to the formation of the primary rainbow.) The overall effect is that part of the incoming light is reflected back over the range of 0° to 42°, with the most intense light at 42°. This angle is independent of the size of the drop, but does depend on its refractive index. Seawater has a higher refractive index than rain water, so the radius of a "rainbow" in sea spray is smaller than that of a true rainbow. This is visible to the naked eye by a misalignment of these bows.

The reason the returning light is most intense at about 42° is that this is a turning point - light hitting the outermost ring of the drop gets returned at less than 42°, as does the light hitting the drop nearer to its centre. There is a circular band of light that all gets returned right around 42°. If the Sun were a laser emitting parallel, monochromatic rays, then the luminance (brightness) of the bow would tend toward infinity at this angle if interference effects are ignored . But since the Sun's luminance is finite and its rays are not all parallel (it covers about half a degree of the sky) the luminance does not go to infinity. Furthermore, the amount by which light is refracted depends upon its wavelength, and hence its colour. This effect is called dispersion. Blue light (shorter wavelength) is refracted at a greater angle than red light, but due to the reflection of light rays from the back of the droplet, the blue light emerges from the droplet at a smaller angle to the original incident white light ray than the red light. Due to this angle, blue is seen on the inside of the arc of the primary rainbow, and red on the outside. The result of this is not only to give different colours to different parts of the rainbow, but also to diminish the brightness. (A "rainbow" formed by droplets of a liquid with no dispersion would be white, but brighter than a normal rainbow.)

The light at the back of the raindrop does not undergo total internal reflection, and most of the light emerges from the back. However, light coming out the back of the raindrop does not create a rainbow between the observer and the Sun because spectra emitted from the back of the raindrop do not have a maximum of intensity, as the other visible rainbows do, and thus the colours blend together rather than forming a rainbow.

A rainbow does not exist at one particular location. Many rainbows exist; however, only one can be seen depending on the particular observer's viewpoint as droplets of light illuminated by the sun. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer's eye. This light is what constitutes the rainbow for that observer. The whole system composed by the Sun's rays, the observer's head, and the (spherical) water drops has an axial symmetry around the axis through the observer's head and parallel to the Sun's rays. The rainbow is curved because the set of all the raindrops that have the right angle between the observer, the drop, and the Sun, lie on a cone pointing at the sun with the observer at the tip. The base of the cone forms a circle at an angle of 40-42° to the line between the observer's head and their shadow but 50% or more of the circle is below the horizon, unless the observer is sufficiently far above the earth's surface to see it all, for example in an aeroplane (see below). Alternatively, an observer with the right vantage point may see the full circle in a fountain or waterfall spray. Conversely, at lower latitudes near midday (specifically, when the sun's elevation exceeds 42 degrees) a rainbow will not be visible against the sky.[better source needed ]

Mathematical derivation

Given a spherical raindrop, and defining the perceived angle of the rainbow as 22 φ, and the angle of the internal reflection as β, then the angle of incidence of the Sun's rays with respect to the drop's surface normal is . Since the angle of refraction is β, Snell's law gives us

where n = 1.333 is the refractive index of water. Solving for φ, we get

The rainbow will occur where the angle φ is maximum with respect to the angle β. Therefore, from calculus, we can set , and solve for β, which yields

Substituting back into the earlier equation for φ yields ≈ 42° as the radius angle of the rainbow.

For red light (wavelength 750nm, n = 1.330 based on the dispersion relation of water), the radius angle is 42.5°; for blue light (wavelength 350nm, n = 1.343), the radius angle is 40.6°.

Variations

Double rainbows

Double rainbow with Alexander's band visible between the primary and secondary bows. Also note the pronounced supernumerary bows inside the primary bow.

A secondary rainbow, at a greater angle than the primary rainbow, is often visible. The term double rainbow is used when both the primary and secondary rainbows are visible. In theory, all rainbows are double rainbows, but since the secondary bow is always fainter than the primary, it may be too weak to spot in practice.

Secondary rainbows are caused by a double reflection of sunlight inside the water droplets. Technically the secondary bow is centred on the sun itself, but since its angular size is more than 90° (about 127° for violet to 130° for red), it is seen on the same side of the sky as the primary rainbow, about 10° outside it at an apparent angle of 50-53°. As a result of the "inside" of the secondary bow being "up" to the observer, the colours appear reversed compared to those of the primary bow.

The secondary rainbow is fainter than the primary because more light escapes from two reflections compared to one and because the rainbow itself is spread over a greater area of the sky. Each rainbow reflects white light inside its coloured bands, but that is "down" for the primary and "up" for the secondary. The dark area of unlit sky lying between the primary and secondary bows is called Alexander's band, after Alexander of Aphrodisias, who first described it.

Twinned rainbow

Unlike a double rainbow that consists of two separate and concentric rainbow arcs, the very rare twinned rainbow appears as two rainbow arcs that split from a single base. The colours in the second bow, rather than reversing as in a secondary rainbow, appear in the same order as the primary rainbow. A "normal" secondary rainbow may be present as well. Twinned rainbows can look similar to, but should not be confused with supernumerary bands. The two phenomena may be told apart by their difference in colour profile: supernumerary bands consist of subdued pastel hues (mainly pink, purple and green), while the twinned rainbow shows the same spectrum as a regular rainbow. The cause of a twinned rainbow is believed to be the combination of different sizes of water drops falling from the sky. Due to air resistance, raindrops flatten as they fall, and flattening is more prominent in larger water drops. When two rain showers with different-sized raindrops combine, they each produce slightly different rainbows which may combine and form a twinned rainbow. A numerical ray tracing study showed that a twinned rainbow on a photo could be explained by a mixture of 0.40 and 0.45 mm droplets. That small difference in droplet size resulted in a small difference in flattening of the droplet shape, and a large difference in flattening of the rainbow top.

Full-circle rainbow

In theory, every rainbow is a circle, but from the ground, usually only its upper half can be seen. Since the rainbow's centre is diametrically opposed to the Sun's position in the sky, more of the circle comes into view as the sun approaches the horizon, meaning that the largest section of the circle normally seen is about 50% during sunset or sunrise. Viewing the rainbow's lower half requires the presence of water droplets below the observer's horizon, as well as sunlight that is able to reach them. These requirements are not usually met when the viewer is at ground level, either because droplets are absent in the required position, or because the sunlight is obstructed by the landscape behind the observer. From a high viewpoint such as a high building or an aircraft, however, the requirements can be met and the full-circle rainbow can be seen. Like a partial rainbow, the circular rainbow can have a secondary bow or supernumerary bows as well. It is possible to produce the full circle when standing on the ground, for example by spraying a water mist from a garden hose while facing away from the sun.

A circular rainbow should not be confused with the glory, which is much smaller in diameter and is created by different optical processes. In the right circumstances, a glory and a (circular) rainbow or fog bow can occur together. Another atmospheric phenomenon that may be mistaken for a "circular rainbow" is the 22° halo, which is caused by ice crystals rather than liquid water droplets, and is located around the Sun (or Moon), not opposite it.

Supernumerary rainbows

In certain circumstances, one or several narrow, faintly coloured bands can be seen bordering the violet edge of a rainbow; i.e., inside the primary bow or, much more rarely, outside the secondary. These extra bands are called supernumerary rainbows or supernumerary bands; together with the rainbow itself the phenomenon is also known as a stacker rainbow. The supernumerary bows are slightly detached from the main bow, become successively fainter along with their distance from it, and have pastel colours (consisting mainly of pink, purple and green hues) rather than the usual spectrum pattern. The effect becomes apparent when water droplets are involved that have a diameter of about 1 mm or less; the smaller the droplets are, the broader the supernumerary bands become, and the less saturated their colours. Due to their origin in small droplets, supernumerary bands tend to be particularly prominent in fogbows.

Supernumerary rainbows cannot be explained using classical geometric optics. The alternating faint bands are caused by interference between rays of light following slightly different paths with slightly varying lengths within the raindrops. Some rays are in phase, reinforcing each other through constructive interference, creating a bright band; others are out of phase by up to half a wavelength, cancelling each other out through destructive interference, and creating a gap. Given the different angles of refraction for rays of different colours, the patterns of interference are slightly different for rays of different colours, so each bright band is differentiated in colour, creating a miniature rainbow. Supernumerary rainbows are clearest when raindrops are small and of uniform size. The very existence of supernumerary rainbows was historically a first indication of the wave nature of light, and the first explanation was provided by Thomas Young in 1804.

Reflected rainbow, reflection rainbow

When a rainbow appears above a body of water, two complementary mirror bows may be seen below and above the horizon, originating from different light paths. Their names are slightly different.

A reflected rainbow may appear in the water surface below the horizon. The sunlight is first deflected by the raindrops, and then reflected off the body of water, before reaching the observer. The reflected rainbow is frequently visible, at least partially, even in small puddles.

A reflection rainbow may be produced where sunlight reflects off a body of water before reaching the raindrops, if the water body is large, quiet over its entire surface, and close to the rain curtain. The reflection rainbow appears above the horizon. It intersects the normal rainbow at the horizon, and its arc reaches higher in the sky, with its centre as high above the horizon as the normal rainbow's centre is below it. Reflection bows are usually brightest when the sun is low because at that time its light is most strongly reflected from water surfaces. As the sun gets lower the normal and reflection bows are drawn closer together. Due to the combination of requirements, a reflection rainbow is rarely visible.

Up to eight separate bows may be distinguished if the reflected and reflection rainbows happen to occur simultaneously: the normal (non-reflection) primary and secondary bows above the horizon (1, 2) with their reflected counterparts below it (3, 4), and the reflection primary and secondary bows above the horizon (5, 6) with their reflected counterparts below it (7, 8).

Monochrome rainbow

Occasionally a shower may happen at sunrise or sunset, where the shorter wavelengths like blue and green have been scattered and essentially removed from the spectrum. Further scattering may occur due to the rain, and the result can be the rare and dramatic monochrome or red rainbow.

Higher-order rainbows

In addition to the common primary and secondary rainbows, it is also possible for rainbows of higher orders to form. The order of a rainbow is determined by the number of light reflections inside the water droplets that create it: One reflection results in the first-order or primary rainbow; two reflections create the second-order or secondary rainbow. More internal reflections cause bows of higher orders-theoretically unto infinity. As more and more light is lost with each internal reflection, however, each subsequent bow becomes progressively dimmer and therefore increasingly difficult to spot. An additional challenge in observing the third-order (or tertiary) and fourth-order ( quaternary) rainbows is their location in the direction of the sun (about 40° and 45° from the sun, respectively), causing them to become drowned in its glare.

For these reasons, naturally occurring rainbows of an order higher than 2 are rarely visible to the naked eye. Nevertheless, sightings of the third-order bow in nature have been reported, and in 2011 it was photographed definitively for the first time. Shortly after, the fourth-order rainbow was photographed as well, and in 2014 the first ever pictures of the fifth-order (or quinary) rainbow were published. The quinary rainbow lies partially in the gap between the primary and secondary rainbows and is far fainter than even the secondary. In a laboratory setting, it is possible to create bows of much higher orders. Felix Billet (1808-1882) depicted angular positions up to the 19th-order rainbow, a pattern he called a "rose of rainbows". In the laboratory, it is possible to observe higher-order rainbows by using extremely bright and well collimated light produced by lasers. Up to the 200th-order rainbow was reported by Ng et al. in 1998 using a similar method but an argon ion laser beam.

Tertiary and quaternary rainbows should not be confused with "triple" and "quadruple" rainbows-terms sometimes erroneously used to refer to the (much more common) supernumerary bows and reflection rainbows.

Rainbows under moonlight

Like most atmospheric optical phenomena, rainbows can be caused by light from the Sun, but also from the Moon. In case of the latter, the rainbow is referred to as a lunar rainbow or . They are much dimmer and rarer than solar rainbows, requiring the Moon to be near-full in order for them to be seen. For the same reason, moonbows are often perceived as white and may be thought of as monochrome. The full spectrum is present, however, but the human eye is not normally sensitive enough to see the colours. Long exposure photographs will sometimes show the colour in this type of rainbow.

Fogbows form in the same way as rainbows, but they are formed by much smaller cloud and fog droplets that diffract light extensively. They are almost white with faint reds on the outside and blues inside; often one or more broad supernumerary bands can be discerned inside the inner edge. The colours are dim because the bow in each colour is very broad and the colours overlap. Fogbows are commonly seen over water when air in contact with the cooler water is chilled, but they can be found anywhere if the fog is thin enough for the sun to shine through and the sun is fairly bright. They are very large-almost as big as a rainbow and much broader. They sometimes appear with a glory at the bow's centre.

Fog bows should not be confused with ice halos, which are very common around the world and visible much more often than rainbows (of any order), yet are unrelated to rainbows.

A sleetbow forms in the same way as a typical rainbow, with the exception that it occurs when light passes through falling sleet (ice pellets) instead of liquid water. As light passes through the sleet, the light is refracted causing the rare phenomena. These have been documented across United States with the earliest publicly documented and photographed sleetbow being seen in Richmond, Virginia on 21 December 2012. Just like regular rainbows, these can also come in various forms, with a monochrome sleetbow being documented on 7 January 2016 in Valparaiso, Indiana.[citation needed ]

Circumhorizontal and circumzenithal arcs

The circumzenithal and circumhorizontal arcs are two related optical phenomena similar in appearance to a rainbow, but unlike the latter, their origin lies in light refraction through hexagonal ice crystals rather than liquid water droplets. This means that they are not rainbows, but members of the large family of halos.

Both arcs are brightly coloured ring segments centred on the zenith, but in different positions in the sky: The circumzenithal arc is notably curved and located high above the Sun (or Moon) with its convex side pointing downwards (creating the impression of an "upside down rainbow"); the circumhorizontal arc runs much closer to the horizon, is more straight and located at a significant distance below the Sun (or Moon). Both arcs have their red side pointing towards the Sun and their violet part away from it, meaning the circumzenithal arc is red on the bottom, while the circumhorizontal arc is red on top.

The circumhorizontal arc is sometimes referred to by the misnomer "fire rainbow". In order to view it, the Sun or Moon must be at least 58° above the horizon, making it a rare occurrence at higher latitudes. The circumzenithal arc, visible only at a solar or lunar elevation of less than 32°, is much more common, but often missed since it occurs almost directly overhead.

Extraterrestrial rainbows

It has been suggested that rainbows might exist on Saturn's moon Titan, as it has a wet surface and humid clouds. The radius of a Titan rainbow would be about 49° instead of 42°, because the fluid in that cold environment is methane instead of water. Although visible rainbows may be rare due to Titan's hazy skies, infrared rainbows may be more common, but an observer would need infrared night vision goggles to see them.

Rainbows with different materials

Droplets (or spheres) composed of materials with different refractive indices than plain water produce rainbows with different radius angles. Since salt water has a higher refractive index, a sea spray bow does not perfectly align with the ordinary rainbow, if seen at the same spot. Tiny plastic or glass marbles may be used in road marking as a reflectors to enhance its visibility by drivers at night. Due to a much higher refractive index, rainbows observed on such marbles have a noticeably smaller radius. One can easily reproduce such phenomena by sprinkling liquids of different refractive indices in the air, as illustrated in the photo.

The displacement of the rainbow due to different refractive indices can be pushed to a peculiar limit. For a material with a refractive index larger than 2, there is no angle fulfilling the requirements for the first order rainbow. For example, the index of refraction of diamond is about 2.4, so diamond spheres would produce rainbows starting from the second order, omitting the first order. In general, as the refractive index exceeds a number n + 1, where n is a natural number, the critical incidence angle for n times internally reflected rays escapes the domain . This results in a rainbow of the n-th order shrinking to the antisolar point and vanishing.

Scientific history

The classical Greek scholar Aristotle (384-322 BC) was first to devote serious attention to the rainbow. According to Raymond L. Lee and Alistair B. Fraser, "Despite its many flaws and its appeal to Pythagorean numerology, Aristotle's qualitative explanation showed an inventiveness and relative consistency that was unmatched for centuries. After Aristotle's death, much rainbow theory consisted of reaction to his work, although not all of this was uncritical."

In Book I of Naturales Quaestiones ( c. 65 AD), the Roman philosopher Seneca the Younger discusses various theories of the formation of rainbows extensively, including those of Aristotle. He notices that rainbows appear always opposite to the Sun, that they appear in water sprayed by a rower, in the water spat by a fuller on clothes stretched on pegs or by water sprayed through a small hole in a burst pipe. He even speaks of rainbows produced by small rods (virgulae) of glass, anticipating Newton's experiences with prisms. He takes into account two theories: one, that the rainbow is produced by the Sun reflecting in each water drop, the other, that it is produced by the Sun reflected in a cloud shaped like a concave mirror; he favours the latter. He also discusses other phenomena related to rainbows: the mysterious "virgae" (rods), halos and parhelia.

According to Hüseyin Gazi Topdemir, the Arab physicist and polymath Ibn al-Haytham (965-1039 AD) attempted to provide a scientific explanation for the rainbow phenomenon. In his Maqala fi al-Hala wa Qaws Quzah ( On the Rainbow and Halo), al-Haytham "explained the formation of rainbow as an image, which forms at a concave mirror. If the rays of light coming from a farther light source reflect to any point on axis of the concave mirror, they form concentric circles in that point. When it is supposed that the sun as a farther light source, the eye of viewer as a point on the axis of mirror and a cloud as a reflecting surface, then it can be observed the concentric circles are forming on the axis."[citation needed ] He was not able to verify this because his theory that "light from the sun is reflected by a cloud before reaching the eye" did not allow for a possible experimental verification. This explanation was repeated by Averroes,[citation needed ] and, though incorrect, provided the groundwork for the correct explanations later given by Kamāl al-Dīn al-Fārisī in 1309 and, independently, by Theodoric of Freiberg (c. 1250-c. 1311)[citation needed ]-both having studied al-Haytham's Book of Optics.

In Song dynasty China (960-1279), a polymath scholar-official named Shen Kuo (1031-1095) hypothesised-as a certain Sun Sikong (1015-1076) did before him-that rainbows were formed by a phenomenon of sunlight encountering droplets of rain in the air. Paul Dong writes that Shen's explanation of the rainbow as a phenomenon of atmospheric refraction "is basically in accord with modern scientific principles."

According to Nader El-Bizri, the Persian astronomer, Qutb al-Din al-Shirazi (1236-1311), gave a fairly accurate explanation for the rainbow phenomenon. This was elaborated on by his student, Kamāl al-Dīn al-Fārisī (1267-1319), who gave a more mathematically satisfactory explanation of the rainbow. He "proposed a model where the ray of light from the sun was refracted twice by a water droplet, one or more reflections occurring between the two refractions." An experiment with a water-filled glass sphere was conducted and al-Farisi showed the additional refractions due to the glass could be ignored in his model. As he noted in his Kitab Tanqih al-Manazir ( The Revision of the Optics), al-Farisi used a large clear vessel of glass in the shape of a sphere, which was filled with water, in order to have an experimental large-scale model of a rain drop. He then placed this model within a camera obscura that has a controlled aperture for the introduction of light. He projected light unto the sphere and ultimately deduced through several trials and detailed observations of reflections and refractions of light that the colours of the rainbow are phenomena of the decomposition of light.

In Europe, Ibn al-Haytham's Book of Optics was translated into Latin and studied by Robert Grosseteste. His work on light was continued by Roger Bacon, who wrote in his Opus Majus of 1268 about experiments with light shining through crystals and water droplets showing the colours of the rainbow. In addition, Bacon was the first to calculate the angular size of the rainbow. He stated that the rainbow summit can not appear higher than 42° above the horizon. Theodoric of Freiberg is known to have given an accurate theoretical explanation of both the primary and secondary rainbows in 1307. He explained the primary rainbow, noting that "when sunlight falls on individual drops of moisture, the rays undergo two refractions (upon ingress and egress) and one reflection (at the back of the drop) before transmission into the eye of the observer." He explained the secondary rainbow through a similar analysis involving two refractions and two reflections.

Descartes' 1637 treatise, Discourse on Method, further advanced this explanation. Knowing that the size of raindrops did not appear to affect the observed rainbow, he experimented with passing rays of light through a large glass sphere filled with water. By measuring the angles that the rays emerged, he concluded that the primary bow was caused by a single internal reflection inside the raindrop and that a secondary bow could be caused by two internal reflections. He supported this conclusion with a derivation of the law of refraction (subsequently to, but independently of, Snell) and correctly calculated the angles for both bows. His explanation of the colours, however, was based on a mechanical version of the traditional theory that colours were produced by a modification of white light.

Isaac Newton demonstrated that white light was composed of the light of all the colours of the rainbow, which a glass prism could separate into the full spectrum of colours, rejecting the theory that the colours were produced by a modification of white light. He also showed that red light is refracted less than blue light, which led to the first scientific explanation of the major features of the rainbow. Newton's corpuscular theory of light was unable to explain supernumerary rainbows, and a satisfactory explanation was not found until Thomas Young realised that light behaves as a wave under certain conditions, and can interfere with itself.

Young's work was refined in the 1820s by George Biddell Airy, who explained the dependence of the strength of the colours of the rainbow on the size of the water droplets. Modern physical descriptions of the rainbow are based on Mie scattering, work published by Gustav Mie in 1908. Advances in computational methods and optical theory continue to lead to a fuller understanding of rainbows. For example, Nussenzveig provides a modern overview.

Experiments

Experiments on the rainbow phenomenon using artificial raindrops, i.e. water-filled spherical flasks, go back at least to Theodoric of Freiberg in the 14th century. Later, also Descartes studied the phenomenon using a Florence flask. A flask experiment known as Florence's rainbow is still often used today as an imposing and intuitively accessible demonstration experiment of the rainbow phenomenon. It consists in illuminating (with parallel white light) a water-filled spherical flask through a hole in a screen. A rainbow will then appear thrown back / projected on the screen, provided the screen is large enough. Due to the finite wall thickness and the macroscopic character of the artificial raindrop, several subtle differences exist as compared to the natural phenomenon, including slightly changed rainbow angles and a splitting of the rainbow orders.

A very similar experiment consists in using a cylindrical glass vessel filled with water or a solid transparent cylinder and illuminated either parallel to the circular base (i.e. light rays remaining at a fixed height while they transit the cylinder) or under an angle to the base. Under these latter conditions the rainbow angles change relative to the natural phenomenon since the effective index of refraction of water changes (Bravais' index of refraction for inclined rays applies).

Other experiments use small liquid drops (see text above).

Culture and mythology

1803 depiction by Joseph Anton Koch of the rainbow in the Book of Genesis

Niagara, by Frederic Edwin Church (1857), depicts a rainbow at the Horseshoe Falls section of Niagara Falls.

Rainbows occur frequently in mythology, and have been used in the arts. The first literary occurrence of a rainbow is in the Book of Genesis chapter 9, as part of the flood story of Noah, where it is a sign of God's covenant to never destroy all life on Earth with a global flood again. In Norse mythology, the rainbow bridge Bifröst connects the world of men ( Midgard) and the realm of the gods ( Asgard). Cuchavira was the god of the rainbow for the Muisca in present-day Colombia and when the regular rains on the Bogotá savanna were over the people thanked him, offering gold, snails and small emeralds. Some forms of Tibetan Buddhism or Dzogchen reference a rainbow body. The Irish leprechaun's secret hiding place for his pot of gold is usually said to be at the end of the rainbow. This place is appropriately impossible to reach, because the rainbow is an optical effect which cannot be approached. In Greek mythology, the goddess Iris is the personification of the rainbow, a messenger goddess who, like the rainbow, connects the mortal world with the gods through messages. In Albanian folk beliefs the rainbow is regarded as the belt of the goddess Prende, and oral legend has it that anyone who jumps over the rainbow changes their sex.

In heraldry, the rainbow proper consists of 4 bands of colour ( argent, gules, or, and vert) with the ends resting on clouds. Generalised examples in coat of arms include those of the towns of Regen and Pfreimd, both in Bavaria, Germany; of Bouffémont, France; and of the 69th Infantry Regiment (New York) of the United States Army National Guard.

Rainbow flags have been used for centuries. It was a symbol of the Cooperative movement in the German Peasants' War in the 16th century, of peace in Italy, and of LGBT pride and LGBT social movements; the rainbow flag as a symbol of LGBT pride and the June pride month since it was designed by Gilbert Baker in 1978. In 1994, Archbishop Desmond Tutu and President Nelson Mandela described newly democratic post- apartheid South Africa as the rainbow nation. The rainbow has also been used in technology product logos, including the Apple computer logo. Many political alliances spanning multiple political parties have called themselves a " Rainbow Coalition".

References

Further reading

Boyer, Carl B. (1987). The Rainbow, From Myth to Mathematics. Princeton University Press. ISBN 978-0-691-08457-2.

Graham, Lanier F., ed. (1976). The Rainbow Book. Berkeley, California: Shambhala Publications and The Fine Arts Museums of San Francisco. (Large format handbook for the Summer 1976 exhibition The Rainbow Art Show which took place primarily at the De Young Museum but also at other museums. The book is divided into seven sections, each coloured a different colour of the rainbow.)

Greenler, Robert (1980). Rainbows, Halos, and Glories. Cambridge University Press. ISBN 978-0-19-521833-6.

Lee, Raymond L. & Alastair B. Fraser (2001). The Rainbow Bridge: Rainbows in Art, Myth and Science. New York: Pennsylvania State University Press and SPIE Press. ISBN 978-0-271-01977-2.

Lynch, David K.; Livingston, William (2001). Color and Light in Nature (2nd ed.). Cambridge University Press. ISBN 978-0-521-77504-5.

Minnaert, Marcel G.J.; Lynch, David K.; Livingston, William (1993). Light and Color in the Outdoors. Springer-Verlag. ISBN 978-0-387-97935-9.

Minnaert, Marcel G.J.; Lynch, David K.; Livingston, William (1973). The Nature of Light and Color in the Open Air. Dover Publications. ISBN 978-0-486-20196-2.

Naylor, John; Lynch, David K.; Livingston, William (2002). Out of the Blue: A 24-Hour Skywatcher's Guide. Cambridge University Press. ISBN 978-0-521-80925-2.

The Mathematics of Rainbows, article from the American mathematical society

Interactive simulation of light refraction in a drop (java applet)

Rainbow seen through infrared filter and through ultraviolet filter

Atmospheric Optics website by Les Cowley - Description of multiple types of bows, including: "bows that cross, red bows, twinned bows, coloured fringes, dark bands, spokes", etc.

Merrifield, Michael. "Rainbows". Sixty Symbols. Brady Haran for the University of Nottingham.

Creating Circular and Double Rainbows! - video explanation of basics, shown artificial rainbow at night, second rainbow and circular one.

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A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the Sun.

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The ancient Greek noun Ἶρις means both the rainbow[2] and the halo of the Moon.

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In ancient Greek religion and mythology, Iris (; EYE-riss; Greek: , Îris, "rainbow," Ancient Greek: ) is a daughter of the gods Thaumas and Electra, the personification of the rainbow and messenger of the gods, a servant to the Olympians and especially Queen Hera. Iris appears in several stories carrying messages from and to the gods or running errands but has no unique mythology of her own. Similarly, very little to none of a historical cult and worship of Iris is attested in surviving records, with only a few traces surviving from the island of Delos. In ancient art, Iris is depicted as a winged young woman carrying a caduceus, the symbol of the messengers, and a pitcher of water for the gods. Iris was traditionally seen as the consort of Zephyrus, the god of the west wind and one of the four Anemoi, by whom she is the mother of Pothos in some versions.

The ancient Greek noun means both the rainbow and the halo of the Moon. An inscription from Corinth provides evidence for an original form ( wîris) with a digamma that was eventually dropped. The noun seems to be of pre-Greek origin. A Proto-Indo-European pre-form has been suggested, although Beekes finds it 'hard to motivate.'

[Morpheus and Iris fr] by Pierre-Narcisse Guérin (1811)

According to Hesiod's , Iris is the daughter of Thaumas and the Oceanid Electra and the sister of the Harpies: Arke and Ocypete. During the Titanomachy, Iris was the messenger of the Olympian gods while her sister Arke betrayed the Olympians and became the messenger of the gods' enemy, the Titans. She is the goddess of the rainbow. She also serves nectar to the goddesses and gods to drink. Zephyrus, who is the god of the west wind, is her consort. Together they had a son named Pothos, or alternatively they were the parents of Eros, the god of love, according to sixth century BC Greek lyric poet Alcaeus, though Eros is usually said to be the son of Ares and Aphrodite. According to the Dionysiaca of Nonnus, Iris' brother is Hydaspes.

She is also known as one of the goddesses of the sea and the sky. Iris links the gods to humanity. She travels with the speed of wind from one end of the world to the other and into the depths of the sea and the underworld.

Winged female figure holding a caduceus: Iris (messenger of the gods) or Nike (Victory)

Iris is said to travel on the rainbow while carrying messages from the gods to mortals. In some records, Iris is a sister to fellow messenger goddess Arke ("swift", "quick"), who flew out of the company of Olympian gods to join the Titans as their messenger goddess during the Titanomachy, making the two sisters enemy messenger goddesses. After the war was won by Zeus and his allies, Zeus tore Arke's wings from her and in time gave them as a gift to the Nereid Thetis at her wedding to Peleus, who in turn gave them to her son, Achilles, who wore them on his feet. Achilles was sometimes known as podarkes (feet like [the wings of] Arke). Podarces was also the original name of Priam, the king of Troy.

Iris stands behind the seated Juno (right) in a Pompeii fresco

Following her daughter Persephone's abduction by Hades, the goddess of agriculture Demeter withdrew to her temple in Eleusis and made the earth barren, causing a great famine that killed off mortals, and as a result sacrifices to the gods ceased. Zeus then sent Iris to Demeter, calling her to join the other gods and lift her curse; but as her daughter was not returned, Demeter was not persuaded.

In one narrative, after Leto and her children pleaded with Zeus to release Prometheus from his torment, Zeus relented, and sent Iris to order Heracles to free the unfortunate Prometheus.

After Ceyx drowned in a shipwreck, Hera made Iris convey her orders to Hypnos, the god of sleep. Iris flew and found him in his cave, and informed him that Hera wished for Ceyx's wife, Alcyone, to be informed of her loved one's death in her dreams. After delivering Hera's command, Iris left immediately, not standing to be near Hypnos for too long, for his powers took hold of her, and made her dizzy and sleepy.

In Aristophanes's comedy , the titular birds build a city in the sky and plan to supplant the Olympian gods. Iris, as the messenger, goes to meet them, but she is ridiculed, insulted, and threatened with rape by their leader Pisetaerus, an elderly Athenian man. Iris appears confused that Pisetearus does not know who the gods are and that she is one of them. Pisetaerus then tells her that the birds are the gods now, the deities whom the humans must sacrifice to. After Pisetaerus threatens to rape her, Iris scolds him for his foul language and leaves, warning him that Zeus, whom she refers to as her father, will deal with him and make him pay.

Iris also appears several times in Virgil's , usually as an agent of Juno. In Book 4, Juno dispatches her to pluck a lock of hair from the head of Queen Dido, so that she may die and enter Hades. In book 5, Iris, having taken on the form of a Trojan woman, stirs up the other Trojan mothers to set fire to four of Aeneas' ships in order to prevent them from leaving Sicily.

Iris Carrying the Water of the River Styx to Olympus for the Gods to Swear By, by Guy Head (c. 1793)

According to the Roman poet Ovid, after Romulus was deified as the god Quirinus, his wife Hersilia pleaded with the gods to let her become immortal as well so that she could be with her husband once again. Juno heard her plea and sent Iris down to her. With a single finger, Iris touched Hersilia and transformed her into an immortal goddess. Hersilia flew to Olympus, where she became one of the Horae and was permitted to live with her husband forevermore.

According to the lost epic by Stasinus, it was Iris who informed Menelaus, who had sailed off to Crete, of what had happened back in Sparta while he was gone, namely his wife Helen's elopement with the Trojan Prince Paris as well as the death of Helen's brother Castor.

Iris is frequently mentioned as a divine messenger in , which is attributed to Homer. She does not, however, appear in The Odyssey, where her role is instead filled by Hermes. Like Hermes, Iris carries a caduceus or winged staff. By command of Zeus, the king of the gods, she carries a ewer of water from the River Styx, with which she puts to sleep all who perjure themselves. In Book XXIII, she delivers Achilles's prayer to Boreas and Zephyrus to light the funeral pyre of Patroclus. In the last book, Zeus sends Iris to King Priam, to tell him that he should go to the Achaean camp alone and ransom the body of his slain son Hector from Achilles. Iris swiftly delivers the message to Priam and returns to Olympus.

Iris, Attic lekythos in Six's technique (superposed colours), circa 500-490 BC, found in Tanagra, now in Louvre.

According to the " Homeric Hymn to Apollo", when Leto was in labor prior to giving birth to her twin children Apollo and Artemis, all the goddesses were in attendance except for two, Hera and Eileithyia, the goddess of childbirth. On the ninth day of her labor, Leto told Iris to bribe Eileithyia and ask for her help in giving birth to her children, without allowing Hera to find out. According to Callimachus, Iris along with Ares ordered, on Hera's orders, all cities and other places to shun the pregnant Leto and deny her shelter where she could bring forth her twins. After Asteria, now transformed into the island of Delos, offered shelter to Leto, Iris flew back to Hera to inform her that Leto had been allowed to give birth due to Asteria defying Hera's orders, and took her seat beside Hera.

According to Apollonius Rhodius, Iris turned back the Argonauts Zetes and Calais, who had pursued the Harpies to the Strophades ("Islands of Turning"). The brothers had driven off the monsters from their torment of the prophet Phineus, but did not kill them upon the request of Iris, who promised that Phineus would not be bothered by the Harpies again.

After King Creon of Thebes forbade the burial of the dead Argive soldiers who had raised their arms against Thebes, Hera ordered Iris to moisturize their dead bodies with dew and ambrosia.

In a lesser-known narrative, Iris once came close to being raped by the satyrs after she attempted to disrupt their worship of Dionysus, perhaps at the behest of Hera. About fifteen black-and-red-figure vase paintings dating from the fifth century BC depict said satyrs either menacingly advancing toward or getting hold of her when she tries to interfere with the sacrifice. In another cup, Iris is depicted being assaulted by the satyrs, who apparently are trying to prevent Iris from stealing sacrificial meat from the altar of Dionysus, who is also present in the scene. On the other side, the satyrs are attacking Hera, who stands between Hermes and Heracles. The ancient playwright Achaeus wrote Iris, a now lost satyr play, which might have been the source of those vases' subject.

In Euripides' play Heracles Gone Mad, Iris appears alongside Lyssa, the goddess of madness and insanity, cursing Heracles with the fit of madness in which he kills his three sons and his wife Megara. Iris also prepared the bed of Zeus and Hera.

Weber-Laborde head Louvre, possibly the head of Iris.

Iris, sculpture from the west pediment of the Parthenon, now at the British Museum.[34]

Unlike the other prominent messenger god of the Greeks, Hermes, Iris did not play a large part in the ancient Greek religion and was rarely worshipped. There are no known temples, shrines, or sanctuaries to Iris, or festivals held in her honour. While she is frequently depicted on vases and in bas-reliefs, few statues are known to have been made of Iris during antiquity. She was however depicted in sculpture on the west pediment of Parthenon in Athens.

Iris does appear to have been the object of at least some minor worship, but the only trace preserved of her cult is the note by Athenaeus in Scholars at Dinner that the people of Delos sacrificed to Iris, offering her cheesecakes called basyniae, a type of cake of wheat-flour, suet, and honey, boiled up together.

Iris had numerous poetic titles and epithets, including chrysopteros (χρυσόπτερος "golden winged"), podas ōkea ( "swift footed") or podēnemos ōkea (ποδήνεμος ὠκέα "wind-swift footed"), roscida ("dewy", Latin), and Thaumantias or Thaumantis (Θαυμαντιάς , , "Daughter of Thaumas, Wondrous One"), aellopus ( "storm-footed, storm-swift). She also watered the clouds with her pitcher, obtaining the water from the sea.

Iris is represented either as a rainbow or as a beautiful young maiden with wings on her shoulders. As a goddess, Iris is associated with communication, messages, the rainbow, and new endeavors. This personification of a rainbow was once described as being a link to the heavens and earth.

In some texts she is depicted wearing a coat of many colors. With this coat she actually creates the rainbows she rides to get from place to place. Iris' wings were said to be so beautiful that she could even light up a dark cavern, a trait observable from the story of her visit to Somnus in order to relay a message to Alcyone.

While Iris was principally associated with communication and messages, she was also believed to aid in the fulfillment of humans' prayers, either by fulfilling them herself or by bringing them to the attention of other deities.

The plant iris was named after her due to the wide variety of colours its flowers have.

7 Iris, a main-belt asteroid named after this goddess.

The chemical element iridium was named after Iris for its colorful salts.

Apollodorus, Apollodorus, The Library, with an English Translation by Sir James George Frazer, F.B.A., F.R.S. in 2 Volumes. Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1921. Online version at the Perseus Digital Library.

Apollonius Rhodius, Argonautica translated by Robert Cooper Seaton (1853-1915), R. C. Loeb Classical Library Volume 001. London, William Heinemann Ltd, 1912. Online version at the Topos Text Project.

Callimachus. Hymns, translated by Alexander William Mair (1875-1928). London: William Heinemann; New York: G.P. Putnam's Sons. 1921. Online version at the Topos Text Project.

Hesiod, , in The Homeric Hymns and Homerica with an English Translation by Hugh G. Evelyn-White, Cambridge, MA., Harvard University Press; London, William Heinemann Ltd. 1914. Online version at the Perseus Digital Library.

Homer, The Iliad with an English Translation by A.T. Murray, PhD in two volumes. Cambridge, MA., Harvard University Press; London, William Heinemann, Ltd. 1924. Online version at the Perseus Digital Library.

Evelyn-White, Hugh, The Homeric Hymns and Homerica with an English Translation by Hugh G. Evelyn-White. Homeric Hymns. Cambridge, Massachusetts, Harvard University Press; London, William Heinemann Ltd. 1914.

Euripides, The Complete Greek Drama', edited by Whitney J. Oates and Eugene O'Neill, Jr. in two volumes. 2. The Phoenissae, translated by E. P. Coleridge. New York. Random House. 1938.

Ovid. Metamorphoses, Volume I: Books 1-8. Translated by Frank Justus Miller. Revised by G. P. Goold. Loeb Classical Library No. 42. Cambridge, Massachusetts: Harvard University Press, 1977, first published 1916. ISBN 978-0-674-99046-3. Online version at Harvard University Press.

Statius, , Volume II: Thebaid: Books 8-12. . Edited and translated by D. R. Shackleton Bailey. Loeb Classical Library 498. Cambridge, MA: Harvard University Press, 2004.

Theocritus, Idylls and Epigrams with an Epilogue, translation by Daryl Hine, New York, Atheneum, 1982, ISBN 0-689-11320-X.

Valerius Flaccus, Argonautica. Translated by J. H. Mozley. Loeb Classical Library 286. Cambridge, MA: Harvard University Press, 1934.

Vergil, Theodore C. Williams. trans. Boston. Houghton Mifflin Co. 1910. Online version at the Perseus Digital Library.

Antonopoulos, Andreas P.; Christopoulos, Menelaos M.; Harrison, George W. M. (July 5, 2021). Reconstructing Satyr Drama. De Gruyter. ISBN 9783110725216.

Beekes, Robert S. P. (2009). Etymological Dictionary of Greek. Leiden: Brill Publications. p. 1:598.

Grimal, Pierre (1996). "Iris". The Dictionary of Classical Mythology. ISBN 978-0-631-20102-1. pp. 237-238.

Peyré, Yves (2009). "Iris". A Dictionary of Shakespeare's Classical Mythology, ed. Yves Peyré.

Sells, Donald (2019). Parody, Politics and the Populace in Greek Old Comedy. Bloomsbury Academic. ISBN 978-1-3500-6051-7.

Welsh, Alexander (2014). The Humanist Comedy. New Haven, Connecticut: Yale University Press. ISBN 978-0-300-19751-8.

Smith, William (1873). "Iris". Dictionary of Greek and Roman Biography and Mythology. London.

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In ancient Greek religion and mythology, Iris (; EYE-riss ; Greek: , Îris , "rainbow," Ancient Greek: ) is a daughter of the gods Thaumas and Electra, the personification of the rainbow and messenger of the gods, a servant to the Olympians and especially Queen Hera.

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It takes its name from the Greek word ἶρις îris "rainbow", which is also the name for the Greek goddess of the rainbow, Iris.

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Iris is a genus of 260-300 species of flowering plants with showy flowers. It takes its name from the Greek word for a rainbow, which is also the name for the Greek goddess of the rainbow, Iris. Some authors state that the name refers to the wide variety of flower colors found among the many species. As well as being the scientific name, iris is also widely used as a common name for all Iris species, as well as some belonging to other closely related genera. A common name for some species is 'flags', while the plants of the subgenus are widely known as ' junos', particularly in horticulture. It is a popular garden flower.

The often-segregated, monotypic genera Belamcanda (blackberry lily, I. domestica), Hermodactylus (snake's head iris, I. tuberosa), and Pardanthopsis (vesper iris, I. dichotoma) are currently included in Iris.

Three Iris varieties are used in the Iris flower data set outlined by Ronald Fisher in his 1936 paper The use of multiple measurements in taxonomic problems as an example of linear discriminant analysis.

Irises are perennial plants, growing from creeping rhizomes (rhizomatous irises) or, in drier climates, from bulbs (bulbous irises). They have long, erect flowering stems which may be simple or branched, solid or hollow, and flattened or have a circular cross-section. The rhizomatous species usually have 3-10 basal sword-shaped leaves growing in dense clumps. The bulbous species have cylindrical, basal leaves.

The inflorescences are in the shape of a fan and contain one or more symmetrical six-lobed flowers. These grow on a pedicel or peduncle. The three sepals, which are usually spreading or droop downwards, are referred to as "falls". They expand from their narrow base (the "claw" or "haft"), into a broader expanded portion ("limb" or "blade") and can be adorned with veining, lines or dots. In the centre of the blade, some of the rhizomatous irises have a "beard" (a tuft of short upright extensions growing in its midline), which are the plant's filaments.

The three, sometimes reduced, petals stand upright, partly behind the sepal bases. They are called "standards". Some smaller iris species have all six lobes pointing straight outwards, but generally limb and standards differ markedly in appearance. They are united at their base into a floral tube that lies above the ovary (known as an epigynous or inferior ovary). The styles divide towards the apex into petaloid branches; this is significant in pollination.

The iris flower is of interest as an example of the relation between flowering plants and pollinating insects. The shape of the flower and the position of the pollen-receiving and stigmatic surfaces on the outer petals form a landing-stage for a flying insect, which in probing for nectar, will first come into contact with the perianth, then with the stigmatic stamens in one whorled surface which is borne on an ovary formed of three carpels. The shelf-like transverse projection on the inner whorled underside of the stamens is beneath the overarching style arm below the stigma, so that the insect comes in contact with its pollen-covered surface only after passing the stigma; in backing out of the flower it will come in contact only with the non-receptive lower face of the stigma. Thus, an insect bearing pollen from one flower will, in entering a second, deposit the pollen on the stigma; in backing out of a flower, the pollen which it bears will not be rubbed off on the stigma of the same flower.

The iris fruit is a capsule which opens up in three parts to reveal the numerous seeds within. In some species, the seeds bear an aril.

Iris is the largest genus of the family Iridaceae with up to 300 species - many of them natural hybrids. Modern classifications, starting with Dykes (1913), have subdivided them. Dykes referred to the major subgroupings as sections. Subsequent authors such as Lawrence (1953) and Rodionenko (1987) have generally called them subgenera, while essentially retaining Dykes' groupings, using six subgenera further divided into twelve sections. Of these, section Limneris (subgenus Limneris) was further divided into sixteen series. Like some older sources, Rodionenko moved some of the bulbous subgenera ( Xiphium, Scorpiris and Hermodactyloides) into separate genera ( Xiphion, and Iridodictyum respectively), but this has not been accepted by later writers such as Mathew (1989), although the latter kept Hermodactylus as a distinct genus, to include Hermodactylus tuberosus, now returned to Hermodactyloides as Iris tuberosa.

Rodionenko also reduced the number of sections in subgenus Iris, from six to two, depending on the presence ( Hexapogon) or absence ( Iris) of arils on the seeds, referred to as arilate or nonarilate. Taylor (1976) provides arguments for not including all arilate species in Hexapogon.

In general, modern classifications usually recognise six subgenera, of which five are restricted to the Old World; the sixth (subgenus Limniris) has a Holarctic distribution. The two largest subgenera are further divided into sections.

Iris (Bearded rhizomatous irises)

Limniris (Beardless rhizomatous irises)

(Smooth-bulbed bulbous irises: Formerly genus Xiphion)

Nepalensis (Bulbous irises: Formerly genus Junopsis)

(Smooth-bulbed bulbous irises: Formerly genus )

Hermodactyloides (Reticulate-bulbed bulbous irises: Formerly genus Iridodictyum)

Sections, series and species

Nearly all species are found in temperate Northern hemisphere zones, from Europe to Asia and across North America. Although diverse in ecology, Iris is predominantly found in dry, semi-desert, or colder rocky mountainous areas, other habitats include grassy slopes, meadowlands, bogs and riverbanks.

Iris is extensively grown as ornamental plant in home and botanical gardens. Presby Memorial Iris Gardens in New Jersey, for example, is a living iris museum with over 10,000 plants, while in Europe the most famous iris garden is arguably the Giardino dell'Iris in Florence (Italy) which every year hosts a well attended iris breeders' competition. Irises, especially the multitude of bearded types, feature regularly in shows such as the Chelsea Flower Show.

For garden cultivation, iris classification differs from taxonomic classification. Garden iris are classed as either bulb iris or rhizome iris (called rhizomatous) with a number of further subdivisions. Due to a wide variety of geographic origins, and thus great genetic diversity, cultivation needs of iris vary greatly.

Iris grow well in most any garden soil types providing they are well-drained. The earliest to bloom are species like and I. reichenbachii, which flower as early as February and March in the Northern Hemisphere, followed by the dwarf forms of , and then by most of the tall bearded varieties, such as the German iris and its variety florentina, sweet iris, Hungarian iris, lemon-yellow iris (I. flavescens), Iris sambucina, , and their natural and horticultural hybrids such as those described under names like I. neglecta or I. squalens and best united under .

The iris is promoted in the United Kingdom by the British Iris Society. The national collection of Arthur Bliss Irises is held by Anne Milner in Gloucestershire.

Bearded iris are classified as dwarf, tall, or aril. In Europe, the most commonly found garden iris is a hybrid iris (falsely called German iris, I. germanica which is sterile) and its numerous cultivars. Various wild forms (including Iris aphylla) and naturally occurring hybrids of the Sweet iris ( I. pallida) and the Hungarian iris (I. variegata) form the basis of almost all modern hybrid bearded irises. Median forms of bearded iris (intermediate bearded, or IB; miniature tall bearded, or MTB; etc.) are derived from crosses between tall and dwarf species like Iris pumila.

Bearded iris are easy to cultivate and propagate and have become very popular in gardens. A small selection is usually held by garden centres at appropriate times during the season, but there are thousands of cultivars available from specialist suppliers (more than 30 000 cultivars only for the tall bearded irises !). They are best planted as bare root plants in late summer, in a sunny open position with the rhizome visible on the surface of the soil and facing the sun. They should be divided in summer every two or three years, when the clumps become congested.

A truly red bearded iris, like a truly blue rose, remains an unattained goal despite frequent hybridizing and selection. There are species and selections, most notably based on the beardless rhizomatous Copper iris (), which have a relatively pure red color. However, getting this color into a modern bearded iris breed has proven very difficult, and thus, the vast majority of irises are in the purple and blue range of the color spectrum, with yellow, pink, orange and white breeds also available.

The following is a selection of bearded irises that have gained the Royal Horticultural Society's Award of Garden Merit:

'Alizes' (tall bearded, blue & white)

'Bumblebee Deelite' (miniature tall bearded, yellow/purple)

'Early Light' (tall bearded, pale yellow)

'Jane Phillips' (tall bearded, pale blue)

'Langport Wren' (intermediate bearded, maroon)

'Maui Moonlight' (intermediate bearded, pale yellow)

'Orinoco Flow' (border bearded, white/violet)

'Raspberry Blush' (intermediate bearded, pink)

'Sarah Taylor' (dwarf bearded, pale yellow)

'Thornbird' (tall bearded, pale yellow)

'Titan's Glory' (tall bearded, deep blue)

Bearded iris Oncocyclus section

This section contains the cushion irises or royal irises, a group of plants noted for their large, strongly marked flowers. Between 30 and 60 species are classified in this section, depending on the authority. Compared with other irises the cushion varieties are scantily furnished with narrow sickle-shaped leaves and the flowers are usually borne singly on the stalks; they are often very dark and in some almost blackish. The cushion irises are somewhat fastidious growers, and to be successful with them they must be planted rather shallow in very gritty well-drained soil. They should not be disturbed in the autumn, and after the leaves have withered the roots should be protected from heavy rains until growth starts again naturally.

Bearded iris Regelia section

This section, closely allied to the cushion irises, includes several garden hybrids with species in section Oncocyclus, known as Regelio-cyclus irises. They are best planted in September or October in warm sunny positions, the rhizomes being lifted the following July after the leaves have withered.

There are six major subgroupings of the beardless iris, depending on origin. They are divided into Pacific Coast, Siberica, Spuria, Louisiana, Japanese, and other.

Beardless rhizomatous iris types commonly found in the European garden are the Siberian iris ( I. sibirica) and its hybrids, and the Japanese Iris () and its hybrids. " Japanese iris" is also a catch-all term for the Japanese iris proper ( hanashōbu), the blood iris (I. sanguinea, ayame) and the rabbit-ear iris ( I. laevigata, kakitsubata). I. unguicularis is a late-winter-flowering species from Algeria, with sky-blue flowers blotched with yellow, produced from Winter to Spring. Yet another beardless rhizomatous iris popular in gardening is I. ruthenica, which has much the same requirements and characteristics as the tall bearded irises. In North America, Louisiana iris and its hybrids are often cultivated.

One specific species, Iris cristata from North America.

Often called ' junos', this type of iris is one of the more popular bulb irises in cultivation. They are generally earliest to bloom.

This group includes irises generally of European descent, and are also classified as Dutch, English, or Spanish iris.

Iris reticulata and Iris persica, both of which are fragrant, are also popular with florists.

Iris xiphium, the Spanish Iris (also known as Dutch Iris) and

Iris latifolia, the English Iris. Despite the common names both the Spanish and English iris are of Spanish origin, and have very showy flowers, so they are popular with gardeners and florists. They are among the hardier bulbous irises, and can be grown in northern Europe. They require to be planted in thoroughly drained beds in very light open soil, moderately enriched, and should have a rather sheltered position. Both these present a long series of beautiful varieties of the most diverse colours, flowering in May, June and July, the smaller Spanish iris being the earlier of the two.

Reticulate irises with their characteristic bulbs, including the yellow I. danfordiae, and the various blue-purple I. histrioides and I. reticulata, flower as early as February and March. These reticulate-bulbed irises are miniatures and popular spring bulbs, being one of the first to bloom in the garden. Many of the smaller species of bulbous iris, being liable to perish from excess of moisture, should have a well-drained bed of good but porous soil made up for them, in some sunny spot, and in winter should be protected by a covering of half-decayed leaves or fresh coco-fiber.

Rhizomes of the German Iris ( I. germanica) and Sweet Iris ( I. pallida) are traded as orris root and are used in perfume and medicine, though more common in ancient times than today. Today Iris essential oil ( absolute) from flowers are sometimes used in aromatherapy as sedative medicines. The dried rhizomes are also given whole to babies to help in teething. Gin brands such as Bombay Sapphire and Magellan Gin use orris root and sometimes iris flowers for flavor and color.

For orris root production, iris rhizomes are harvested, dried, and aged for up to 5 years. In this time, the fats and oils inside the roots undergo degradation and oxidation, which produces many fragrant compounds that are valuable in perfumery. The scent is said to be similar to violets. The aged rhizomes are steam-distilled which produces a thick oily compound, known in the perfume industry as "iris butter" or orris oil.

Iris rhizomes also contain notable amounts of terpenes, and organic acids such as ascorbic acid, myristic acid, tridecylenic acid and undecylenic acid. Iris rhizomes can be toxic. Larger blue flag (I. versicolor) and other species often grown in gardens and widely hybridized contain elevated amounts of the toxic glycoside iridin. These rhizomes can cause nausea, vomiting, diarrhea, and/or skin irritation, but poisonings are not normally fatal. Irises should only be used medicinally under professional guidance.

In water purification, yellow iris ( I. pseudacorus) is often used. The roots are usually planted in a substrate (e.g. lava-stone) in a reedbed-setup. The roots then improve water quality by consuming nutrient pollutants, such as from agricultural runoff. This highly aggressive grower is now considered a noxious weed and banned in some states of the US where it is found clogging natural waterways.

The Iris is one of the flowers listed as birth flower for February. In Christianity, the iris represents Our Lady of Sorrows as its sharp leaves are like swords.

The Iris croatica is the unofficial National Flower of Croatia . Iris nigricans, the Black Iris is the national flower of Jordan. Iris bismarckiana, the Nazareth Iris, is the symbol of the city of Upper Nazareth.

In 1998, Iris lacustris, the Dwarf Lake Iris was designated the state wildflower of Michigan, where the vast majority of populations exist.

In 1990, the Louisiana iris was voted the state wildflower of Louisiana, though the state flower is the magnolia blossom.

An iris - species unspecified - is one of the state flowers of Tennessee. It is generally accepted that the species Iris versicolor, the Purple Iris is the state flower alongside the wild-growing purple passionflower ( Passiflora incarnata), the state's other floral emblem. Greeneville, Tennessee, is home to the annual Iris Festival celebrating the iris, local customs, and culture. The species Iris versicolor is also the provincial flower of Quebec, having replaced the Madonna lily which is not native to the province. and it is the official flower of Kappa Pi International Honorary Art Fraternity.

The artist George Gessert has specialised in breeding irises.

The artist Vincent van Gogh painted several famous pictures of irises.

The American artist Joseph Mason - a friend of John James Audubon - painted a precise image of what was then known as the Louisiana flag or copper iris (), to which Audubon subsequently added two Northern paraula birds (Parula americana) for inclusion as Plate 15 in his Birds of America.

The artist Philip Hermogenes Calderon painted an iris in his 1856 work Broken Vows; he followed the principles of the Pre-Raphaelite Brotherhood. An ancient belief is that the iris serves as a warning to be heeded, as it was named for the messenger of Olympus. It also conveys images of lost love and silent grief, for young girls were led into the afterlife by Iris. Broken Vows was accompanied with poetry by Henry Wadsworth Longfellow when it was first exhibited.

French King Clovis I (466-511), when he converted to Christianity, changed his symbol on his banner from three toads to irises (the Virgin's flower).

The fleur-de-lis, a stylized iris, first occurs in its modern use as the emblem of the House of Capet. The fleur-de-lis has been associated with France since Louis VII adopted it as a symbol in the 12th century. The yellow fleur-de-lis reflects the yellow iris ( I. pseudacorus), common in Western Europe. Contemporary uses can be seen in the Quebec flag and the logo of the New Orleans Saints professional football team and on the flag of Saint Louis, Missouri.

The red fleur-de-lis in the coat-of-arms and flag of Florence, Italy, descends from the white iris which is native to Florence and which grew even in its city walls. This white iris displayed against a red background was the symbol of Florence until the Medici family reversed the colors to signal a change in political power, setting in motion a centuries-long and still on-going breeding program to hybridize a red iris.

The fleur-de-lis is the almost-universal symbol of Scouting and one of the symbols adopted by the sorority Kappa Kappa Gamma.

A stylized yellow iris is the symbol of Brussels, since historically the important Saint Gaugericus Island was carpeted in them. The iris symbol is now the sole feature on the flag of the Brussels-Capital Region. The provincial flower of Québec ( Canada) is the harlequin blueflag ( I. versicolor), called iris versicolore in French.

It is thought in China, that Iris anguifuga has the ability to keep snakes from entering the garden. It grows all winter, keeping snakes out, but then goes dormant in the spring, allowing the snakes back into the garden. In the autumn, the iris re-appears and can stop the snakes again.

In the Homeric Hymn to Demeter, the goddess Persephone and her companion nymphs (the Oceanids along with Artemis and Athena) were gathering flowers such as rose, crocus, violet, iris (also called 'agallis' or ἀγαλλίς (in Greek script), lily, larkspur, and hyacinth in a springtime meadow before she was abducted by the god Hades.

It has been suggested that the 'agallis' mentioned was a dwarf iris, as described by leaf and root shape,) and identified as Iris attica.

Chancery of the Prime Minister, Kingdom of Belgium [2007]: Brussels Town Hall. Retrieved November 11, 2007.

Rina Kamenetsky; Hiroshi Okubo, eds. (2012). "Iridaceae". Ornamental Geophytes: From Basic Science to Sustainable Production. CRC Press. p. 24. ISBN 978-1-4398-4924-8.

Mancoff, Debra N. (2003): Flora Symbolica: Flowers in Pre-Raphaelite Art. Prestel Publishing, New York, USA. ISBN 3-7913-2851-4.

Pioch, Nicolas (2002): Gogh, Vincent van: Irises. Bersion of 2002-AUG-19. Retrieved December 10, 2008.

Species Group of the British Iris Society (1996): A Guide to Species Irises: Their Identification and Cultivation; Cambridge University Press, Cambridge, UK. ISBN 0-521-44074-2.

West, Ruth [2008]: George Gessert. Retrieved December 10, 2008.

American Iris Society. Systematic Treatment of the Genus Iris by Baker. 2012

Dykes, W. R. (1913): The Genus Iris. Cambridge University Press, Cambridge, UK. ISBN 0486230376

Harris, Gwenda. CLASSIFICATION OF IRISES. New Zealand Iris Society 2011

Brian Mathew. The Iris. Batsford, London 1989

George Hill Mathewson Lawrence. A Reclassification of the Genus Iris. Gentes Herb 8:346-371 1953

Rodionenko, G. I.: The Genus Iris L. (Questions of Morphology, Biology, Evolution and Systematics). British Iris Society, London 1987. (trans.)

Taylor, J.J. 1976. A reclassification of Iris species bearing arillate seeds. Proceedings of the Biological Society, Washington. 89: 411-420.

Wilson, Carol. Phylogeny of the genus Iris based on DNA sequence data. Rancho Santa Ana 2004

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Iris is a genus of 260-300 species of flowering plants with showy flowers. It takes its name from the Greek word for a rainbow, which is also the name for the Greek goddess of the rainbow, Iris. Some authors state that the name refers to the wide variety of flower colors found among the many species.

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Species Plantarum ( Latin for "The Species of Plants") is a book by Carl Linnaeus, originally published in 1753, which lists every species of plant known at the time, classified into genera. It is the first work to consistently apply binomial names and was the starting point for the naming of plants.

was published on 1 May 1753 by Laurentius Salvius in Stockholm, in two volumes. A second edition was published in 1762-1763, and a third edition in 1764, although this "scarcely differed" from the second. Further editions were published after Linnaeus' death in 1778, under the direction of Karl Ludwig Willdenow, the director of the Berlin Botanical Garden; the fifth edition (1800) was published in four volumes.

was the first botanical work to consistently apply the binomial nomenclature system of naming to any large group of organisms (Linnaeus' tenth edition of would apply the same technique to animals for the first time in 1758). Prior to this work, a plant species would be known by a long polynomial, such as Plantago foliis ovato-lanceolatis pubescentibus, spica cylindrica, scapo tereti (meaning " plantain with pubescent ovate-lanceolate leaves, a cylindrical spike and a terete scape") or Nepeta floribus interrupte spicatis pedunculatis (meaning " Nepeta with flowers in a stalked, interrupted spike"). In , these cumbersome names were replaced with two-part names, consisting of a single-word genus name, and a single-word specific epithet or "trivial name"; the two examples above became Plantago media and Nepeta cataria, respectively. The use of binomial names had originally been developed as a kind of shorthand in a student project about the plants eaten by cattle.

After the specific epithet, Linnaeus gave a short description of each species, and a synonymy. The descriptions were careful and terse, consisting of few words in small genera; in Glycyrrhiza, for instance, the three species (Glycyrrhiza echinata, Glycyrrhiza glabra and " Glycyrrhiza hirsuta", respectively) were described as "leguminibus echinatis ", "" and "".

Because it is the first work in which binomial nomenclature was consistently applied, was chosen as the "starting point" for the nomenclature of most plants (the nomenclature of some non-vascular plants and all fungi uses later starting points).

contained descriptions of the thousands of plant species known to Linnaeus at the time. In the first edition, there were 5,940 names, from Acalypha australis to Zygophyllum spinosum. In his introduction, Linnaeus estimated that there were fewer than 10,000 plant species in existence; there are now thought to be around 400,000 species of flowering plants alone.

The species were arranged in around a thousand genera, which were grouped into 24 classes, according to Linnaeus' sexual system of classification. There are no descriptions of the genera in ; these are supplied in the companion volume ("the genera of plants"), the fifth edition of which was printed at a similar time to the first edition of . Linnaeus' sexual system is now acknowledged to be an artificial system, rather than one which accurately reflects shared ancestry, but the system's simplicity made it easier for non-specialists to rapidly find the correct class, being based on simple counts of floral parts such as stigmas and stamens.

1. ^ "Carolus Linnæus, Species Plantarum, Stockholm 1762-3". Collection Highlight Summer 2007. University of Aberdeen. 2007. Archived from the original on 30 April 2018.

2. ^ Winston, Judith (20 April 2012). Describing Species: Practical Taxonomic Procedure for Biologists. Columbia University Press. p. 35. ISBN 9780231506656.

3. ^ McNeill, J.; Barrie, F.R.; Buck, W.R.; Demoulin, V.; Greuter, W.; Hawksworth, D.L.; Herendeen, P.S.; Knapp, S.; Marhold, K.; Prado, J.; Prud'homme Van Reine, W.F.; Smith, G.F.; Wiersema, J.H.; Turland, N.J. (2012). International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011. Vol. Regnum Vegetabile 154. A.R.G. Gantner Verlag KG. ISBN 978-3-87429-425-6.

4. ^ Clive A. Stace (1991). "The development of plant taxonomy". Plant Taxonomy and Biosystematics (2nd ed.). Cambridge University Press. pp. 17-64. ISBN 978-0-521-42785-2.

5. ^ Robert W. Kiger. "Index to Binomials Cited in the First Edition of Linnaeus' Species Plantarum". Hunt Institute for Botanical Documentation. Archived from the original on 12 July 2018.

6. ^ H. G. Bongard (1835). "Historical sketch of the progress of botany in Russia, from the time of Peter the Great to the present day; and on the part which the Academy has borne in the advancement of this science". Companion to the Botanical Magazine. 1: 177-186.

Linnaeus, Carl (1753). Species Plantarum: exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas (1st. ed.). Stockholm: Impensis Laurentii Salvii.

Linnaeus, Carl (1763). Species Plantarum: exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas (2nd. ed.). Stockholm: Impensis Laurentii Salvii.

Linnaeus Link Union Catalogue

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Species Plantarum ( Latin for "The Species of Plants") is a book by Carl Linnaeus, originally published in 1753, which lists every species of plant known at the time, classified into genera. It is the first work to consistently apply binomial names and was the starting point for the naming of plants.

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Spathula foetidissima (L.) Fourr. | Plants of the World Online | Kew Science

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First published in Ann. Soc. Linn. Lyon, n.s., 17: 163 (1869)

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The Iliad (; Ancient Greek: Ἰλιάς, Iliás, Attic Greek: ; "a poem about Ilium (Troy)") is one of two major ancient Greek epic poems attributed to Homer. It is one of the oldest extant works of literature still widely read by modern audiences.

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Pompeian Wall-painting depicting Odysseus (far left) carrying off the Palladion from Troy, with the help of Diomedes (middle) and Eurybates (right) against the resistance of Cassandra (far right), from the National Archaeological Museum of Naples in Italy

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This article Please add a needs attention from an expert in literature. reason or a talk parameter to this template to explain the issue with the article. WikiProject Literature may be able to help recruit an expert.

Chiastic structure, or chiastic pattern, is a literary technique in narrative motifs and other textual passages. An example of chiastic structure would be two ideas, A and B, together with variants A' and B', being presented as A,B,B',A'. Chiastic structures that involve more components are sometimes called "ring structures", "ring compositions", or, in cases of very ambitious chiasmus, "onion-ring compositions". These may be regarded as chiasmus scaled up from words and clauses to larger segments of text.

These often symmetrical patterns are commonly found in ancient literature such as the epic poetry of the and the . Classicist Bruno Gentili describes this technique as "the cyclical, circular, or 'ring' pattern ( ring composition). Here the idea that introduced a compositional section is repeated at its conclusion, so that the whole passage is framed by material of identical content". Meanwhile, in classical prose, scholars often find chiastic narrative techniques in the of Herodotus:

"Herodotus frequently uses ring composition or 'epic regression' as a way of supplying background information for something discussed in the narrative. First an event is mentioned briefly, then its precedents are reviewed in reverse chronological order as far back as necessary; at that point the narrative reverses itself and moves forward in chronological order until the event in the main narrative line is reached again."

Various chiastic structures are also seen in the Hebrew Bible, the New Testament, the Book of Mormon, and the Quran.

The term chiastic derives from the mid-17th century term chiasmus, which refers to a crosswise arrangement of concepts or words that are repeated in reverse order. Chiasmus derives from the Greek word khiasmos, a word that is khiazein, marked with the letter . From khi comes chi.

Chi is made up of two lines crossing each other as in the shape of an X. The line that starts leftmost on top, comes down, and is rightmost on the bottom, and vice versa. If one thinks of the lines as concepts, one sees that concept A, which comes first, is also last, and concept B, which comes after A, comes before A. If one adds in more lines representing other concepts, one gets a chiastic structure with more concepts. See Proverbs 1:20-33; vs 20-21=A, v 22=B, v 23=C, vs 24-25=D, vs 26-28=E, vs 29-30=D', v 31=C', v 32=B', v 33=A'.

Oral literature is especially rich in chiastic structure, possibly as an aid to memorization and oral performance. In his study of Homer's Iliad and Odyssey, Cedric Whitman, for instance, finds chiastic patterns "of the most amazing virtuosity" that simultaneously performed both aesthetic and mnemonic functions, permitting the oral poet easily to recall the basic structure of the composition during performances. Steve Reece has demonstrated several ambitious ring compositions in Homer's Odyssey and compared their aesthetic and mnemonic functions with examples of demonstrably oral Serbo-Croatian epic.

In 1986, William H. Shea proposed that the Book of Daniel is composed of a double-chiasm. He argued that the chiastic structure is emphasized by the two languages that the book is written in: Aramaic and Hebrew. The first chiasm is written in Aramaic from chapters 2-7 following an ABC...CBA pattern. The second chiasm is in Hebrew from chapters 8-12, also using the ABC...CBA pattern. However, Shea represents Daniel 9:26 as "D", a break in the center of the pattern.

Gordon Wenham has analyzed the Genesis Flood narrative and believes that it is essentially an elaborate chiasm. Based on the earlier study of grammatical structure by F. I. Andersen, Wenham illustrated a chiastic structure as displayed in the following two tables.

A: Noah and his sons (Gen 6:10)

B: All life on earth (6:13:a)

C: Curse on earth (6:13:b)

D: Flood announced (6:7)

E: Ark (6:14-16)

F: All living creatures (6:17-20 )

G: Food (6:21)

H: Animals in man's hands (7:2-3)

I: Entering the Ark (7:13-16)

J: Waters increase (7:17-20)
X: God remembers Noah (8:1)

J': Waters decrease (8:13-14)

I': Exiting the Ark (8:15-19)

H': Animals (9:2,3)

G': Food (9:3,4)

F': All living creatures (9:10a)

E': Ark (9:10b)

D': No flood in future (9:11)

C': Blessing on earth (9:12-17)

B': All life on earth (9:16)

A': Noah and his sons (9:18,19a)

Within this overall structure, there is a numerical mini-chiasm of 7s, 40s, and 150s:

α: Seven days waiting to enter Ark (7:4)

β: Second mention of seven days waiting (7:10)

β': Seven days waiting for dove (8:10)

α': Second seven days waiting for dove (8:12)

Form critic, Nils Lund, acknowledged Jewish and classical patterns of writing in the New Testament, including the use of chiastic structures throughout.

The writer of the book of Ephesians uses a chiastic structure to bracket the entire book.

A Grace to you

B and peace... (Eph 1:2)

Bʹ Peace be to the whole community... (Eph. 6:23)

Aʹ Grace be with all. (Eph. 6:24).

Chiastic structure is found throughout the Book of Mormon, for example in Mosiah 5:8-9:

8 And under this head ye are made free, and there is no other head whereby ye can be made free.

A There is no other name given whereby salvation cometh;

B therefore, I would that ye should take upon you the name of Christ,

C all you that have entered into the covenant with God

D that ye should be obedient unto the end of your lives.

9 D And it shall come to pass that whosoever doeth this

C shall be found at the right hand of God,

B for he shall know the name by which he is called;

A for he shall be called by the name of Christ.

While there are many examples of chiastic structure in the Quran, perhaps the most well known is in the 'Verse of the Throne' or 'Ayat al-Kursi'. The verse contains 9 sentences which exhibit chiasmus, but perhaps more interesting is that it is found in the longest chapter of the Quran, Al-Baqara, which itself contains a fractal chiastic structure in its 286 verses, i.e. where each (outer) chiasm is composed of (inner) chiastic structures reflected in some sense in the analogue outer chiasm. One such analysis of the chapter is shown below (from; alternate and/or more detail analyses can be found in,).

A: Belief (1-20)

Aa: Believers (1-5)

Ab: Unbelievers (6-20)

B: God's creation and knowledge (21-39)

Ba: Evidence of God: Life and death, bringing the dead back to life (28)

Bb: God knows all (29-30, 32-33)

C: Early prophets and books (40-103)

Ca: God gave Moses the Book (43, 87)

Cb: Solomon, son of David (102)

D: Trials (104-152)

Da: Abraham tested by God (124)

Db: Abraham and Ishmael built Ka'ba (127)

Dc: Concealing testimony (140)

Dd: People of the book (Jews and Christians) say... (111, 113, 116, 118, 135)

D': Trials (153-177)

Da': Muslims will be tested (155)

Db': Pilgrimage to the Ka'ba (158)

Dc': Concealing God's signs and revelations (159, 174)

Dd': Polytheists say... (167, 170)

C': Early prophets and books (178-253)

Ca': It has been written (prescribed) for you (178, 180, 183, 216)

Cb': David, father of Solomon (251)

B': God's creation and knowledge (254-284)

Ba': Evidence of God: Life and death, bringing the dead back to life (258-260)

Bb': God knows all (255-256,261,268,270-271,273,282-284)

A': Belief (285-286)

Aa': Believers (285)

Ab': Unbelievers (286)

ABC...CBA pattern

In literary texts with a possible oral origin, such as , chiastic or ring structures are often found on an intermediate level, that is, between the (verbal and/or grammatical) level of chiasmus and the higher level of chiastic structure such as noted in the Torah. John D. Niles provides examples of chiastic figures on all three levels. He notes that for the instances of ll. 12-19, the announcement of the birth of (Danish) Beowulf, are chiastic, more or less on the verbal level, that of chiasmus. Then, each of the three main fights are organized chiastically, a chiastic structure on the level of verse paragraphs and shorter passages. For instance, the simplest of these three, the fight with Grendel, is schematized as follows:

A: Preliminaries

Grendel approaching

Grendel rejoicing

Grendel devouring Handscioh

B: Grendel's wish to flee ("fingers cracked")

C: Uproar in hall; Danes stricken with terror
HEOROT IN DANGER OF FALLING

C': Uproar in hall; Danes stricken with terror

B': "Joints burst"; Grendel forced to flee

A': Aftermath

Grendel slinking back toward fens

Beowulf rejoicing

Beowulf left with Grendel's arm

Finally, Niles provides a diagram of the highest level of chiastic structure, the organization of the poem as a whole, in an introduction, three major fights with interludes before and after the second fight (with Grendel's mother), and an epilogue. To illustrate, he analyzes Prologue and Epilogue as follows:

D': Beowulf's order to build his barrow

C': History of Geats after Beowulf ("messenger's prophecy")

B': Beowulf's funeral

The overall chiastic structure of John Milton's Paradise Lost is also of the ABC...CBA type:

A: Satan's sinful actions (Books 1-3)

B: Entry into Paradise (Book 4)

C: War in heaven (destruction) (Books 5-6)

C': Creation of the world (Books 7-8)

B': Loss of paradise (Book 9)

Douglas, Mary (2007). Thinking in Circles: an essay on ring composition. New Haven, CT: Yale University Press. ISBN 978-0-300-16785-6.

Lund, Nils Wilhelm (1942), Chiasmus in the New Testament, a study in formgeschichte, Chapel Hill: University of North Carolina Press, OCLC 2516087

Martin, Gary D. (2004), Ring Composition and Related Phenomena in Herodotus (PDF)

McCoy, Brad (Fall 2003), "Chiasmus: An Important Structural Device Commonly Found in Biblical Literature" (PDF), CTS Journal, 9 (2): 18-34, archived from the original (PDF) on 2012-11-22

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Prewitt, Terry J. (1990), The Elusive Covenant: A Structural-Semiotic Reading of Genesis, Bloomington: Indiana University Press, ISBN 978-0253345998, OCLC 20827915

Ramirez, Matthew Eric (January 2011). "Descanting on Deformity: The Irregularities in Shakespeare's Large Chiasms". Text and Performance Quarterly. 31 (1): 37-49. doi:10.1080/10462937.2010.526240.

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# data[].attributes.attachment_link.description
This article Please add a needs attention from an expert in literature. reason or a talk parameter to this template to explain the issue with the article. WikiProject Literature may be able to help recruit an expert. Chiastic structure, or chiastic pattern, is a literary technique in narrative motifs and other textual passages.

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Pronunciation

Ancient Greek

Its value in Ancient Greek was an aspirated velar stop /kʰ/ (in the Western Greek alphabet: /ks/).

Koine Greek

In Koine Greek and later dialects it became a fricative ([x]/[ç]) along with Θ and Φ.

Modern Greek

In Modern Greek, it has two distinct pronunciations: In front of high or front vowels (/e/ or /i/) it is pronounced as a voiceless palatal fricative [ç], as in German ich or like the h in some pronunciations of the English words hew and human. In front of low or back vowels (/a/, /o/ or /u/) and consonants, it is pronounced as a voiceless velar fricative ([x]), as in German ach.

Transliteration

Chi is romanized as ⟨ch⟩ in most systematic transliteration conventions, but sometimes ⟨kh⟩ is used. In addition, in Modern Greek, it is often also romanized as ⟨h⟩ or ⟨x⟩ in informal practice.

Greek numeral

In the system of Greek numerals, it has a value of 600.

In ancient times, some local forms of the Greek alphabet used the chi instead of xi to represent the /ks/ sound. This was borrowed into the early Latin language, which led to the use of the letter X for the same sound in Latin, and many modern languages that use the Latin alphabet.

Chi was also included in the Cyrillic script as the letter Х, with the phonetic value /x/ or /h/.

International Phonetic Alphabet

In the International Phonetic Alphabet, the minuscule chi is the symbol for the voiceless uvular fricative.

Chi is the basis for the name literary chiastic structure and the name of chiasmus.

In Plato's , it is explained that the two bands that form the soul of the world cross each other like the letter Χ. Plato's analogy, along with several other examples of chi as a symbol occur in Thomas Browne's discourse The Garden of Cyrus (1658).

Chi or X is often used to abbreviate the name Christ, as in the holiday Christmas ( Xmas). When fused within a single typespace with the Greek letter rho, it is called the labarum and used to represent the person of Jesus Christ.

Character encodings

Mathematical chi

These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.

Math and science

In statistics, the term chi-squared or has various uses, including the chi-squared distribution, the chi-squared test, and chi-squared target models.

In algebraic topology, Chi is used to represent the Euler characteristic of a surface.

In neuroanatomy, crossings of peripheral nerves (such as the optic chiasm) are named for the letter Chi because of its Χ-shape.

In chemistry, the mole fraction[6][7] and electronegativity[8] may be denoted by the lowercase .

In physics, denotes electric or magnetic susceptibility.

In rhetoric, both chiastic structure (a literary device) and the figure of speech Chiasmus derive from their names from the shape of the letter Chi.

In mechanical engineering, chi is used as a symbol for the reduction factor of relevant buckling loads in the EN 1993, a European Standard for the design of steel structures.

In graph theory, a lowercase chi is used to represent a graph's chromatic number.

References

# data[].attributes.attachment_link.description
Ancient Greek Its value in Ancient Greek was an aspirated velar stop /kʰ/ (in the Western Greek alphabet: /ks/). Koine Greek In Koine Greek and later dialects it became a fricative ([x]/[ç]) along with Θ and Φ.

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Magnetohydrodynamics ( MHD; also called magneto-fluid dynamics or hydromagnetics) is the study of the magnetic properties and behaviour of electrically conducting fluids. Examples of such magnetofluids include plasmas, liquid metals, salt water, and electrolytes. The word "magnetohydrodynamics" is derived from magneto- meaning magnetic field, hydro- meaning water, and dynamics meaning movement. The field of MHD was initiated by Hannes Alfvén, for which he received the Nobel Prize in Physics in 1970.

The fundamental concept behind MHD is that magnetic fields can induce currents in a moving conductive fluid, which in turn polarizes the fluid and reciprocally changes the magnetic field itself. The set of equations that describe MHD are a combination of the Navier-Stokes equations of fluid dynamics and Maxwell's equations of electromagnetism. These differential equations must be solved simultaneously, either analytically or numerically.

The first recorded use of the word magnetohydrodynamics is by Hannes Alfvén in 1942:

At last some remarks are made about the transfer of momentum from the Sun to the planets, which is fundamental to the theory (§11). The importance of the Magnetohydrodynamic waves in this respect are pointed out.

The ebbing salty water flowing past London's Waterloo Bridge interacts with the Earth's magnetic field to produce a potential difference between the two river-banks. Michael Faraday called this effect "magneto-electric induction" and tried this experiment in 1832 but the current was too small to measure with the equipment at the time, and the river bed contributed to short-circuit the signal. However, by a similar process the voltage induced by the tide in the English Channel was measured in 1851.

Faraday carefully omitted the term of hydrodynamics in this work.

The simplest form of MHD, Ideal MHD, assumes that the fluid has so little resistivity that it can be treated as a perfect conductor. This is the limit of infinite magnetic Reynolds number. In ideal MHD, Lenz's law dictates that the fluid is in a sense tied to the magnetic field lines. To explain, in ideal MHD a small rope-like volume of fluid surrounding a field line will continue to lie along a magnetic field line, even as it is twisted and distorted by fluid flows in the system. This is sometimes referred to as the magnetic field lines being "frozen" in the fluid. The connection between magnetic field lines and fluid in ideal MHD fixes the topology of the magnetic field in the fluid-for example, if a set of magnetic field lines are tied into a knot, then they will remain so as long as the fluid/plasma has negligible resistivity. This difficulty in reconnecting magnetic field lines makes it possible to store energy by moving the fluid or the source of the magnetic field. The energy can then become available if the conditions for ideal MHD break down, allowing magnetic reconnection that releases the stored energy from the magnetic field.

The ideal MHD equations consist of the continuity equation, the Cauchy momentum equation, Ampere's Law neglecting displacement current, and a temperature evolution equation. As with any fluid description to a kinetic system, a closure approximation must be applied to highest moment of the particle distribution equation. This is often accomplished with approximations to the heat flux through a condition of adiabaticity or isothermality.

The main quantities which characterize the electrically conducting fluid are the bulk plasma velocity field v, the current density J, the mass density ρ, and the plasma pressure p. The flowing electric charge in the plasma is the source of a magnetic field electric field B and t. E. All quantities generally vary with time Vector operator notation will be used, in particular ∇ is gradient, ∇ ⋅ is divergence, and ∇ × is curl.

The mass continuity equation is

The Cauchy momentum equation is

The Lorentz force term can be expanded using Ampère's law and the vector calculus identity

to give

where the first term on the right hand side is the magnetic tension force and the second term is the magnetic pressure force.

The ideal Ohm's law for a plasma is given by

Faraday's law is

The low-frequency Ampère's law neglects displacement current and is given by

The magnetic divergence constraint is

The energy equation is given by

where is the ratio of specific heats for an adiabatic equation of state. This energy equation is only applicable in the absence of shocks or heat conduction as it assumes that the entropy of a fluid element does not change.

Ideal MHD is only strictly applicable when:

1. The plasma is strongly collisional, so that the time scale of collisions is shorter than the other characteristic times in the system, and the particle distributions are therefore close to Maxwellian.

2. The resistivity due to these collisions is small. In particular, the typical magnetic diffusion times over any scale length present in the system must be longer than any time scale of interest.

3. Interest in length scales much longer than the ion skin depth and Larmor radius perpendicular to the field, long enough along the field to ignore Landau damping, and time scales much longer than the ion gyration time (system is smooth and slowly evolving).

In an imperfectly conducting fluid the magnetic field can generally move through the fluid following a diffusion law with the resistivity of the plasma serving as a diffusion constant. This means that solutions to the ideal MHD equations are only applicable for a limited time for a region of a given size before diffusion becomes too important to ignore. One can estimate the diffusion time across a solar active region (from collisional resistivity) to be hundreds to thousands of years, much longer than the actual lifetime of a sunspot-so it would seem reasonable to ignore the resistivity. By contrast, a meter-sized volume of seawater has a magnetic diffusion time measured in milliseconds.

Even in physical systems-which are large and conductive enough that simple estimates of the Lundquist number suggest that the resistivity can be ignored-resistivity may still be important: many instabilities exist that can increase the effective resistivity of the plasma by factors of more than 10 ⁹. The enhanced resistivity is usually the result of the formation of small scale structure like current sheets or fine scale magnetic turbulence, introducing small spatial scales into the system over which ideal MHD is broken and magnetic diffusion can occur quickly. When this happens, magnetic reconnection may occur in the plasma to release stored magnetic energy as waves, bulk mechanical acceleration of material, particle acceleration, and heat.

Magnetic reconnection in highly conductive systems is important because it concentrates energy in time and space, so that gentle forces applied to a plasma for long periods of time can cause violent explosions and bursts of radiation.

When the fluid cannot be considered as completely conductive, but the other conditions for ideal MHD are satisfied, it is possible to use an extended model called resistive MHD. This includes an extra term in Ohm's Law which models the collisional resistivity. Generally MHD computer simulations are at least somewhat resistive because their computational grid introduces a numerical resistivity.

Another limitation of MHD (and fluid theories in general) is that they depend on the assumption that the plasma is strongly collisional (this is the first criterion listed above), so that the time scale of collisions is shorter than the other characteristic times in the system, and the particle distributions are Maxwellian. This is usually not the case in fusion, space and astrophysical plasmas. When this is not the case, or the interest is in smaller spatial scales, it may be necessary to use a kinetic model which properly accounts for the non-Maxwellian shape of the distribution function. However, because MHD is relatively simple and captures many of the important properties of plasma dynamics it is often qualitatively accurate and is therefore often the first model tried.

Effects which are essentially kinetic and not captured by fluid models include double layers, Landau damping, a wide range of instabilities, chemical separation in space plasmas and electron runaway. In the case of ultra-high intensity laser interactions, the incredibly short timescales of energy deposition mean that hydrodynamic codes fail to capture the essential physics.

In many MHD systems most of the electric current is compressed into thin nearly-two-dimensional ribbons termed current sheets. These can divide the fluid into magnetic domains, inside of which the currents are relatively weak. Current sheets in the solar corona are thought to be between a few meters and a few kilometers in thickness, which is quite thin compared to the magnetic domains (which are thousands to hundreds of thousands of kilometers across). Another example is in the Earth's magnetosphere, where current sheets separate topologically distinct domains, isolating most of the Earth's ionosphere from the solar wind.

The wave modes derived using MHD plasma theory are called magnetohydrodynamic waves or MHD waves. In general there are three MHD wave modes:

Pure (or oblique) Alfvén wave

Slow MHD wave

Fast MHD wave

All these waves have constant phase velocities for all frequencies, and hence there is no dispersion. At the limits when the angle between the wave propagation vector k and magnetic field B is either 0° (180°) or 90°, the wave modes are called:

The phase velocity depends on the angle between the wave vector k and the magnetic field B. An MHD wave propagating at an arbitrary angle θ with respect to the time independent or bulk field will satisfy the dispersion relation

where

is the Alfvén speed. This branch corresponds to the shear Alfvén mode. Additionally the dispersion equation gives

where

is the ideal gas speed of sound. The plus branch corresponds to the fast-MHD wave mode and the minus branch corresponds to the slow-MHD wave mode.

The MHD oscillations will be damped if the fluid is not perfectly conducting but has a finite conductivity, or if viscous effects are present.

MHD waves and oscillations are a popular tool for the remote diagnostics of laboratory and astrophysical plasmas, for example, the corona of the Sun ( Coronal seismology).

Resistive

Resistive MHD describes magnetized fluids with finite electron diffusivity (η ≠ 0). This diffusivity leads to a breaking in the magnetic topology; magnetic field lines can 'reconnect' when they collide. Usually this term is small and reconnections can be handled by thinking of them as not dissimilar to shocks; this process has been shown to be important in the Earth-Solar magnetic interactions.

Extended

Extended MHD describes a class of phenomena in plasmas that are higher order than resistive MHD, but which can adequately be treated with a single fluid description. These include the effects of Hall physics, electron pressure gradients, finite Larmor Radii in the particle gyromotion, and electron inertia.

Two-fluid

Two-fluid MHD describes plasmas that include a non-negligible Hall electric field. As a result, the electron and ion momenta must be treated separately. This description is more closely tied to Maxwell's equations as an evolution equation for the electric field exists.

Hall

In 1960, M. J. Lighthill criticized the applicability of ideal or resistive MHD theory for plasmas. It concerned the neglect of the "Hall current term", a frequent simplification made in magnetic fusion theory. Hall-magnetohydrodynamics (HMHD) takes into account this electric field description of magnetohydrodynamics. The most important difference is that in the absence of field line breaking, the magnetic field is tied to the electrons and not to the bulk fluid.

Electron MHD

Electron Magnetohydrodynamics (EMHD) describes small scales plasmas when electron motion is much faster than the ion one. The main effects are changes in conservation laws, additional resistivity, importance of electron inertia. Many effects of Electron MHD are similar to effects of the Two fluid MHD and the Hall MHD. EMHD is especially important for z-pinch, magnetic reconnection, ion thrusters, neutron stars, and plasma switches.

Collisionless

MHD is also often used for collisionless plasmas. In that case the MHD equations are derived from the Vlasov equation.

Reduced

By using a multiscale analysis the (resistive) MHD equations can be reduced to a set of four closed scalar equations. This allows for, amongst other things, more efficient numerical calculations.

Beneath the Earth's mantle lies the core, which is made up of two parts: the solid inner core and liquid outer core. Both have significant quantities of iron. The liquid outer core moves in the presence of the magnetic field and eddies are set up into the same due to the Coriolis effect. These eddies develop a magnetic field which boosts Earth's original magnetic field-a process which is self-sustaining and is called the geomagnetic dynamo.

Based on the MHD equations, Glatzmaier and Paul Roberts have made a supercomputer model of the Earth's interior. After running the simulations for thousands of years in virtual time, the changes in Earth's magnetic field can be studied. The simulation results are in good agreement with the observations as the simulations have correctly predicted that the Earth's magnetic field flips every few hundred thousand years. During the flips, the magnetic field does not vanish altogether-it just gets more complex.

Earthquakes

Some monitoring stations have reported that earthquakes are sometimes preceded by a spike in ultra low frequency (ULF) activity. A remarkable example of this occurred before the 1989 Loma Prieta earthquake in California, although a subsequent study indicates that this was little more than a sensor malfunction. On December 9, 2010, geoscientists announced that the DEMETER satellite observed a dramatic increase in ULF radio waves over Haiti in the month before the magnitude 7.0 M w 2010 earthquake. Researchers are attempting to learn more about this correlation to find out whether this method can be used as part of an early warning system for earthquakes.

MHD applies to astrophysics, including stars, the interplanetary medium (space between the planets), and possibly within the interstellar medium (space between the stars) and jets. Most astrophysical systems are not in local thermal equilibrium, and therefore require an additional kinematic treatment to describe all the phenomena within the system (see Astrophysical plasma).

Sunspots are caused by the Sun's magnetic fields, as Joseph Larmor theorized in 1919. The solar wind is also governed by MHD. The differential solar rotation may be the long-term effect of magnetic drag at the poles of the Sun, an MHD phenomenon due to the Parker spiral shape assumed by the extended magnetic field of the Sun.

Previously, theories describing the formation of the Sun and planets could not explain how the Sun has 99.87% of the mass, yet only 0.54% of the angular momentum in the Solar System. In a closed system such as the cloud of gas and dust from which the Sun was formed, mass and angular momentum are both conserved. That conservation would imply that as the mass concentrated in the center of the cloud to form the Sun, it would spin faster, much like a skater pulling their arms in. The high speed of rotation predicted by early theories would have flung the proto-Sun apart before it could have formed. However, magnetohydrodynamic effects transfer the Sun's angular momentum into the outer solar system, slowing its rotation.

Breakdown of ideal MHD (in the form of magnetic reconnection) is known to be the likely cause of solar flares. The magnetic field in a solar active region over a sunspot can store energy that is released suddenly as a burst of motion, X-rays, and radiation when the main current sheet collapses, reconnecting the field.

Magnetohydrodynamic sensors are used for precision measurements of angular velocities in inertial navigation systems such as in aerospace engineering. Accuracy improves with the size of the sensor. The sensor is capable of surviving in harsh environments.

MHD is related to engineering problems such as plasma confinement, liquid-metal cooling of nuclear reactors, and electromagnetic casting (among others).

A magnetohydrodynamic drive or MHD propulsor is a method for propelling seagoing vessels using only electric and magnetic fields with no moving parts, using magnetohydrodynamics. The working principle involves electrification of the propellant (gas or water) which can then be directed by a magnetic field, pushing the vehicle in the opposite direction. Although some working prototypes exist, MHD drives remain impractical.

The first prototype of this kind of propulsion was built and tested in 1965 by Steward Way, a professor of mechanical engineering at the University of California, Santa Barbara. Way, on leave from his job at Westinghouse Electric, assigned his senior-year undergraduate students to develop a submarine with this new propulsion system. In the early 1990s, a foundation in Japan (Ship & Ocean Foundation (Minato-ku, Tokyo)) built an experimental boat, the , which used a magnetohydrodynamic drive incorporating a superconductor cooled by liquid helium, and could travel at 15 km/h.

MHD power generation fueled by potassium-seeded coal combustion gas showed potential for more efficient energy conversion (the absence of solid moving parts allows operation at higher temperatures), but failed due to cost-prohibitive technical difficulties. One major engineering problem was the failure of the wall of the primary-coal combustion chamber due to abrasion.

In microfluidics, MHD is studied as a fluid pump for producing a continuous, nonpulsating flow in a complex microchannel design.

MHD can be implemented in the continuous casting process of metals to suppress instabilities and control the flow.

Industrial MHD problems can be modeled using the open-source software EOF-Library. Two simulation examples are 3D MHD with a free surface for electromagnetic levitation melting, and liquid metal stirring by rotating permanent magnets.

An important task in cancer research is developing more precise methods for delivery of medicine to affected areas. One method involves the binding of medicine to biologically compatible magnetic particles (such as ferrofluids), which are guided to the target via careful placement of permanent magnets on the external body. Magnetohydrodynamic equations and finite element analysis are used to study the interaction between the magnetic fluid particles in the bloodstream and the external magnetic field.

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Magnetohydrodynamics ( MHD; also called magneto-fluid dynamics or hydro­magnetics) is the study of the magnetic properties and behaviour of electrically conducting fluids. Examples of such magneto­fluids include plasmas, liquid metals, salt water, and electrolytes. The word "magneto­hydro­dynamics" is derived from magneto- meaning magnetic field, hydro- meaning water, and dynamics meaning movement.

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Hannes Olof Gösta Alfvén ( Swedish: ; 30 May 1908 - 2 April 1995) was a Swedish electrical engineer, plasma physicist and winner of the 1970 Nobel Prize in Physics for his work on magnetohydrodynamics (MHD). He described the class of MHD waves now known as Alfvén waves. He was originally trained as an electrical power engineer and later moved to research and teaching in the fields of plasma physics and electrical engineering. Alfvén made many contributions to plasma physics, including theories describing the behavior of aurorae, the Van Allen radiation belts, the effect of magnetic storms on the Earth's magnetic field, the terrestrial magnetosphere, and the dynamics of plasmas in the Milky Way galaxy.

Alfvén received his PhD from the University of Uppsala in 1934. His thesis was titled "Investigations of High-frequency Electromagnetic Waves."

In 1934, Alfvén taught physics at both the University of Uppsala and the Nobel Institute for Physics (later renamed the Manne Siegbahn Institute of Physics) in Stockholm, Sweden. In 1940, he became professor of electromagnetic theory and electrical measurements at the Royal Institute of Technology in Stockholm. In 1945, he acquired the nonappointive position of Chair of Electronics. His title was changed to Chair of Plasma Physics in 1963. From 1954 to 1955, Alfvén was a Fulbright Scholar at the University of Maryland, College Park. In 1967, after leaving Sweden and spending time in the Soviet Union, he moved to the United States. Alfvén worked in the departments of electrical engineering at both the University of California, San Diego and the University of Southern California.

In 1991, Alfvén retired as professor of electrical engineering at the University of California, San Diego and professor of plasma physics at the Royal Institute of Technology in Stockholm.

Alfvén spent his later adult life alternating between California and Sweden. He died at the age of 86.

In 1937, Alfvén argued that if plasma pervaded the universe, it could then carry electric currents capable of generating a galactic magnetic field. After winning the Nobel Prize for his works in magnetohydrodynamics, he emphasized that:

In order to understand the phenomena in a certain plasma region, it is necessary to map not only the magnetic but also the electric field and the electric currents. Space is filled with a network of currents which transfer energy and momentum over large or very large distances. The currents often pinch to filamentary or surface currents. The latter are likely to give space, as also interstellar and intergalactic space, a cellular structure.

His theoretical work on field-aligned electric currents in the aurora (based on earlier work by Kristian Birkeland) was confirmed in 1967, these currents now being known as Birkeland currents.

Alfvén's work was disputed for many years by the senior scientist in space physics, the British mathematician and geophysicist Sydney Chapman. Alfvén was regarded as a person with unorthodox opinions in the field by many physicists, R. H. Stuewer noting that "... he remained an embittered outsider, winning little respect from other scientists even after he received the Nobel Prize..." and was often forced to publish his papers in obscure journals. Alfvén recalled:

When I describe [plasma phenomena] according to this formalism most referees do not understand what I say and turn down my papers. With the referee system which rules US science today, this means that my papers are rarely accepted by the leading US journals.

Alfvén played a central role in the development of:

In 1939, Alfvén proposed the theory of magnetic storms and auroras and the theory of plasma dynamics in the earth's magnetosphere. This was the paper rejected by the U.S. journal Terrestrial Magnetism and Atmospheric Electricity.

Applications of Alfvén's research in space science include:

Alfvén's views followed those of the founder of magnetospheric physics, Kristian Birkeland. At the end of the nineteenth century, Birkeland proposed (backed by extensive data) that electric currents flowing down along the Earth's magnetic fields into the atmosphere caused the aurora and polar magnetic disturbances.

Areas of technology benefiting from Alfvén's contributions include:

Contributions to astrophysics:

Galactic magnetic field (1937)

Identified nonthermal synchrotron radiation from astronomical sources (1950)

Alfvén waves (low frequency hydromagnetic plasma oscillations) are named in his honor, and propagate at the Alfvén speed. Many of his theories about the solar system were verified as late as the 1980s through external measurements of cometary and planetary magnetospheres. However, Alfvén himself noted that astrophysical textbooks poorly represented known plasma phenomena:

A study of how a number of the most used textbooks in astrophysics treat important concepts such as double layers, critical velocity, pinch effects, and circuits is made. It is found that students using these textbooks remain essentially ignorant of even the existence of these concepts, despite the fact that some of them have been well known for half a century (e.g, double layers, Langmuir, 1929; pinch effect, Bennet, 1934).

Alfvén reported that of 17 of the most used textbooks on astrophysics, none mention the pinch effect, none mentioned critical ionization velocity, only two mentioned circuits, and three mentioned double layers.

Alfvén believed the problem with the Big Bang was that astrophysicists tried to extrapolate the origin of the universe from mathematical theories developed on the blackboard, rather than starting from known observable phenomena. He also considered the Big Bang to be a myth devised to explain creation. Alfvén and colleagues proposed the Alfvén-Klein model as an alternative cosmological theory to both the Big Bang and steady state theory cosmologies.

Alfvén was married for 67 years to his wife Kerstin (1910-1992). They raised five children, one boy and four girls. Their son became a physician, while one daughter became a writer and another a lawyer in Sweden. The writer was Inger Alfvén and is well known for her work in Sweden. The composer Hugo Alfvén was Hannes Alfvén's uncle.

Alfvén studied the history of science, oriental philosophy, and religion. On his religious views, Alfven was irreligious and critical of religion. He spoke Swedish, English, German, French, and Russian, and some Spanish and Chinese. He expressed great concern about the difficulties of permanent high-level radioactive waste management." Alfvén was also interested in problems in cosmology and all aspects of auroral physics, and used Schröder's well known book on aurora, Das Phänomen des Polarlichts. Letters of Alfvén, Treder, and Schröder were published on the occasion of Treder's 70th birthday. The relationships between Hans-Jürgen Treder, Hannes Alfvén and Wilfried Schröder were discussed in detail by Schröder in his publications.

Alfvén died on 2 April, 1995 at Djursholm aged 86.

The Hannes Alfvén Prize, awarded annually by the European Physical Society for outstanding contributions in plasma physics, is named after him. The asteroid 1778 Alfvén is named in his honour.

Alfvén was one of the few scientists who was a foreign member of both the United States and Soviet Academies of Sciences.

For full list of publications see.

Cosmical Electrodynamics, International Series of Monographs on Physics, Oxford: Clarendon Press, 1950. (See also 2nd Ed. 1963, co-authored with Carl-Gunne Fälthammar.)

Worlds-Antiworlds: Antimatter in Cosmology (1966).

The Great Computer: A Vision (1968) (a political-scientific satire under the pen name Olof Johannesson; publ. Gollancz, ISBN 0-575-00059-7).

Atom, Man, and the Universe: A Long Chain of Complications, W.H. Freeman and Company, 1969.

Living on the Third Planet, authored with Kerstin Alfvén, W.H. Freeman and Company, 1972. ISBN 0-7167-0340-8.

Cosmic Plasma, Astrophysics and Space Science Library, Vol. 82 (1981) Springer Verlag. ISBN 90-277-1151-8

Schröder, Wilfried, and Hans Jürgen Treder. 2007. Theoretical physics and geophysics: Recollections of Hans-Jürgen Treder (1928-2006). Potsdam: Science Editions.

1. ^ "Alfvén, Hannes Olof Gosta". Who Was Who in America, 1993-1996, vol. 11. New Providence, N.J.: Marquis Who's Who. 1996. p. 4. ISBN 978-0-8379-0225-8.

2. ^ Hannes, A (1990). "Cosmology in the Plasma Universe: An Introductory Exposition". IEEE Transactions on Plasma Science. 18 (1): 5-10. Bibcode:1990ITPS...18....5P. doi:10.1109/27.45495. ISSN 0093-3813.

3. ^ Peratt, A. L., Peter, W., & Snell, C. M. (June 19-23, 1989). "3-dimensional particle-in-cell simulations of spiral galaxies". Proceedings of the 140th Symposium of IAU. Galactic and intergalactic magnetic fields. Heidelberg, Federal Republic of Germany: Kluwer Academic Publishers. pp. 143-150. Bibcode:1990IAUS..140..143P.

4. Hannes Alfvén, "Memoirs of a Dissident Scientist", ^ American Scientist, Volume 76, No 3, May-June 1988, pp. 249-251. Quoted in Joseph Paul Martino, Science Funding: Politics and Porkbarrel 1992, Transaction Publishers, ISBN 1-56000-033-3

5. Hannes Alfvén, "^ Double layers and circuits in astrophysics" (1986) IEEE Transactions on Plasma Science (ISSN 0093-3813), vol. PS-14, Dec. 1986, pp. 779-793.

6. ^ Alfvén, Hannes (1984). "Cosmology-Myth or Science?". Journal of Astrophysics and Astronomy. 5 (1): 79-98. Bibcode:1984JApA....5...79A. doi:10.1007/BF02714974. S2CID 122751100.

7. "Nuclear power is uniquely unforgiving: as Swedish Nobel physicist Hannes Alfvén said, "No acts of God can be permitted."" Amory Lovins, ^ Inside NOVA - Nuclear After Japan: Amory Lovins, pbs.org.

8. ^ Helge Kragh (2004). Matter and Spirit in the Universe: Scientific and Religious Preludes to Modern Cosmology. OECD Publishing. p. 252. ISBN 9781860944697. Alfven dismissed in his address religion as a "myth," and passionately criticized the big-bang theory for being dogmatic and violating basic standards of science, to be no less mythical than religion.

9. ^ Abbotts, John (October 1979). "Radioactive waste: A technical solution?". Bulletin of the Atomic Scientists. 35 (8): 12-18. Bibcode:1979BuAtS..35h..12A. doi:10.1080/00963402.1979.11458649.

10. ^ Schröder, Wilfried . 2000. The Aurora in time. (Das Phänomen des Polarlichts). Darmstadt: Reproduction.

11. ^ Fälthammer, C. G. (1997). "Plasma physics from laboratory to cosmos-the life and achievements of Hannes Alfven". IEEE Transactions on Plasma Science. 25 (3): 409-414. Bibcode:1997ITPS...25..409F. doi:10.1109/27.597253. S2CID 123514422.

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Hannes Olof Gösta Alfvén ( Swedish: ; 30 May 1908 - 2 April 1995) was a Swedish electrical engineer, plasma physicist and winner of the 1970 Nobel Prize in Physics for his work on magnetohydrodynamics (MHD). He described the class of MHD waves now known as Alfvén waves.

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Karl Manne Georg Siegbahn FRS(For) H FRSE (3 December 1886 - 26 September 1978) was a Swedish physicist who was awarded the Nobel Prize in Physics in 1924 "for his discoveries and research in the field of X-ray spectroscopy".

Siegbahn was born in Örebro, Sweden, the son of Georg Siegbahn and his wife, Emma Zetterberg.

He graduated in Stockholm 1906 and began his studies at Lund University in the same year. During his education he was secretarial assistant to Johannes Rydberg. In 1908 he studied at the University of Göttingen. He obtained his doctorate (PhD) at the Lund University in 1911, his thesis was titled Magnetische Feldmessungen (magnetic field measurements). He became acting professor for Rydberg when his (Rydberg's) health was failing, and succeeded him as full professor in 1920. However, in 1922 he left Lund for a professorship at Uppsala University.

In 1937, Siegbahn was appointed Director of the Physics Department of the Nobel Institute of the Royal Swedish Academy of Sciences. In 1988 this was renamed the Manne Siegbahn Institute (MSI). The institute research groups have been reorganized since, but the name lives on in the Manne Siegbahn Laboratory hosted by Stockholm University.

Manne Siegbahn began his studies of X-ray spectroscopy in 1914. Initially he used the same type of spectrometer as Henry Moseley had done for finding the relationship between the wavelength of some elements and their place at the periodic system. Shortly thereafter he developed improved experimental apparatus which allowed him to make very accurate measurements of the X-ray wavelengths produced by atoms of different elements. Also, he found that several of the spectral lines that Moseley had discovered consisted of more components. By studying these components and improving the spectrometer, Siegbahn got an almost complete understanding of the electron shell. He developed a convention for naming the different spectral lines that are characteristic to elements in X-ray spectroscopy, the Siegbahn notation. Siegbahn's precision measurements drove many developments in quantum theory and atomic physics.

Siegbahn was awarded the Nobel Prize in Physics in 1924. He won the Hughes Medal 1934 and Rumford Medal 1940. In 1944, he patented the Siegbahn pump. Siegbahn was elected a Foreign Member of the Royal Society in 1954.

Siegbahn married Karin Högbom in 1914. They had two children: Bo Siegbahn (1915-2008), a diplomat and politician, and Kai Siegbahn (1918-2007), a physicist who received the Nobel Prize in Physics in 1981 for his contribution to the development of X-ray photoelectron spectroscopy.

Media related to Manne Siegbahn at Wikimedia Commons

Manne Siegbahn on Nobelprize.org including the Nobel Lecture, December 11, 1925 The X-ray Spectra and the Structure of the Atoms

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Karl Manne Georg Siegbahn FRS(For) H FRSE (3 December 1886 - 26 September 1978) was a Swedish physicist who was awarded the Nobel Prize in Physics in 1924 "for his discoveries and research in the field of X-ray spectroscopy". Siegbahn was born in Örebro, Sweden, the son of Georg Siegbahn and his wife, Emma Zetterberg.

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Third Clue - THE_FINALS_Promo_ISEULT_Candy_3 LMG

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Third Clue - THE_FINALS_Promo_ISEULT_Candy_3 LMG

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1076 Viola , provisional designation 1926 TE, is a Nysian asteroid from the inner regions of the asteroid belt, approximately 22 kilometers in diameter. It was discovered on 5 October 1926, by German astronomer Karl Reinmuth at the Heidelberg Observatory in southwest Germany. The asteroid was named after the flowering plant .

Viola is a non- family asteroid of the main belt's background population when applying the Hierarchical Clustering Method to its proper orbital elements. The asteroid has also been classified as a member of the Nysa family (), the largest asteroid family of the main belt, consisting of stony and carbonaceous subfamilies. The family, named after 44 Nysa, is located near the Kirkwood gap (3:1 orbital resonance with Jupiter), a depleted zone that separates the central main belt.

Viola orbits the Sun in the inner asteroid belt at a distance of 2.1-2.8 AU once every 3 years and 11 months (1,422 days; semi-major axis of 2.47 AU). Its orbit has an eccentricity of 0.14 and an inclination of 3 ° with respect to the ecliptic. The body's observation arc begins at Heidelberg in January 1951, or more than 24 years after its official discovery observation.

In the Tholen classification, Viola is a rare F-type asteroid, while in the SMASS taxonomy, it is classified as a common, carbonaceous C-type.

Rotation period

In the 1980s, a rotational lightcurve of Viola was obtained from photometric observations by American astronomer Richard Binzel. Lightcurve analysis gave a well-defined rotation period of 7.336 hours with a brightness amplitude of 0.12 magnitude (). A tentative period of 14.4 hours was measured by French amateur astronomer René Roy in January 2009, but later retracted from the LCDB ().

Diameter and albedo

According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Viola measures between 21.412 and 26.39 kilometers in diameter and its surface has an albedo between 0.032 and 0.0428.

The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0415 and a diameter of 22.63 kilometers based on an absolute magnitude of 12.30.

This minor planet was named after , a genus of flowering plants within the violet family. The official naming citation was mentioned in The Names of the Minor Planets by Paul Herget in 1955 ().

Reinmuth's flowers

Due to his many discoveries, Karl Reinmuth submitted a large list of 66 newly named asteroids in the early 1930s. The list covered his discoveries with numbers between (1009) and (1200). This list also contained a sequence of 28 asteroids, starting with 1054 Forsytia, that were all named after plants, in particular flowering plants (also see list of minor planets named after animals and plants).

1. ^ "JPL Small-Body Database Browser: 1076 Viola (1926 TE)" (2017-03-29 last obs.). Jet Propulsion Laboratory.

2. ^ Schmadel, Lutz D. (2007). "(1076) Viola". Dictionary of Minor Planet Names - (1076) Viola. Springer Berlin Heidelberg. p. 92. doi:10.1007/978-3-540-29925-7_1077. ISBN 978-3-540-00238-3.

3. ^ "LCDB Data for (1076) Viola". Asteroid Lightcurve Database (LCDB).

4. ^ "Asteroid 1076 Viola - Nesvorny HCM Asteroid Families V3.0". Small Bodies Data Ferret.

5. ^ Masiero, Joseph R.; Grav, T.; Mainzer, A. K.; Nugent, C. R.; Bauer, J. M.; Stevenson, R.; et al. (August 2014). "Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos". The Astrophysical Journal. 791 (2): 11. arXiv:. Bibcode:2014ApJ...791..121M. doi:10.1088/0004-637X/791/2/121.

6. ^ Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T.

7. ^ Binzel, R. P.; Mulholland, J. D. (December 1983). "A photoelectric lightcurve survey of small main belt asteroids". Icarus. 56 (3): 519-533. Bibcode:1983Icar...56..519B. doi:10.1016/0019-1035(83)90170-7. ISSN 0019-1035.

8. ^ is the pronunciation of the musical instrument, rather than the flower that this asteroid is named after.

9. ^ Behrend, Raoul. "Asteroids and comets rotation curves - (1076) Viola". Geneva Observatory.

10. ^ Schmadel, Lutz D. (2007). "(1054) Forsytia". Dictionary of Minor Planet Names - (1054) Forsytia. Springer Berlin Heidelberg. p. 90. doi:10.1007/978-3-540-29925-7_1055. ISBN 978-3-540-00238-3.

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A small satellite, miniaturized satellite, or smallsat is a satellite of low mass and size, usually under 1,200 kg (2,600 lb). While all such satellites can be referred to as "small", different classifications are used to categorize them based on mass. Satellites can be built small to reduce the large economic cost of launch vehicles and the costs associated with construction. Miniature satellites, especially in large numbers, may be more useful than fewer, larger ones for some purposes - for example, gathering of scientific data and radio relay. Technical challenges in the construction of small satellites may include the lack of sufficient power storage or of room for a propulsion system.

One rationale for miniaturizing satellites is to reduce the cost; heavier satellites require larger rockets with greater thrust that also have greater cost to finance. In contrast, smaller and lighter satellites require smaller and cheaper launch vehicles and can sometimes be launched in multiples. They can also be launched 'piggyback', using excess capacity on larger launch vehicles. Miniaturized satellites allow for cheaper designs and ease of mass production.

Another major reason for developing small satellites is the opportunity to enable missions that a larger satellite could not accomplish, such as:

Constellations for low data rate communications

Using formations to gather data from multiple points

In-orbit inspection of larger satellites

University-related research

Testing or qualifying new hardware before using it on a more expensive spacecraft

The nanosatellite and microsatellite segments of the satellite launch industry have been growing rapidly in recent years. Development activity in the 1-50 kg (2.2-110.2 lb) range has been significantly exceeding that in the 50-100 kg (110-220 lb) range.

In the 1-50 kg range alone, fewer than 15 satellites were launched annually in 2000 to 2005, 34 in 2006, then fewer than 30 launches annually during 2007 to 2011. This rose to 34 launched in 2012 and 92 launched in 2013.

European analyst Euroconsult projects more than 500 smallsats being launched in 2015-2019 with a market value estimated at US$7.4 billion.

By mid-2015, many more launch options had become available for smallsats, and rides as secondary payloads had become both greater in quantity and easier to schedule on shorter notice.

The term "small satellite", or sometimes "minisatellite", often refers to an artificial satellite with a wet mass (including fuel) between 100 and 500 kg (220 and 1,100 lb), but in other usage has come to mean any satellite under 500 kg (1,100 lb).

Although smallsats have traditionally been launched as secondary payloads on larger launch vehicles, a number of companies currently are developing or have developed launch vehicles specifically targeted at the smallsat market. In particular, the secondary payload paradigm does not provide the specificity required for many small satellites that have unique orbital and launch-timing requirements.

Companies offering smallsat launch vehicles include:

The term "microsatellite" or "microsat" is usually applied to the name of an artificial satellite with a wet mass between 10 and 100 kg (22 and 220 lb). However, this is not an official convention and sometimes those terms can refer to satellites larger than that, or smaller than that (e.g., 1-50 kg (2.2-110.2 lb)). Sometimes, designs or proposed designs from some satellites of these types have microsatellites working together or in a formation. The generic term "small satellite" or "smallsat" is also sometimes used, as is "satlet".

Examples: Astrid-1 and Astrid-2,[citation needed ] as well as the set of satellites currently announced for LauncherOne (below)

In 2018, the two Mars Cube One microsats-massing just 13.5 kg (30 lb) each-became the first CubeSats to leave Earth orbit for use in interplanetary space. They flew on their way to Mars alongside the successful Mars lander mission. The two microsats accomplished a flyby of Mars in November 2018, and both continued communicating with ground stations on Earth through late December. Both went silent by early January 2019.

A number of commercial and military-contractor companies are currently developing microsatellite launch vehicles to perform the increasingly targeted launch requirements of microsatellites. While microsatellites have been carried to space for many years as secondary payloads aboard larger launchers, the secondary payload paradigm does not provide the specificity required for many increasingly sophisticated small satellites that have unique orbital and launch-timing requirements.

In July 2012, Virgin Galactic announced LauncherOne, an orbital launch vehicle designed to launch "smallsat" primary payloads of 100 kg (220 lb) into low Earth orbit, with launches projected to begin in 2016. Several commercial customers have already contracted for launches, including GeoOptics, Skybox Imaging, Spaceflight Industries, and Planetary Resources. Both Surrey Satellite Technology and Sierra Nevada Space Systems are developing satellite buses "optimized to the design of LauncherOne". Virgin Galactic has been working on the LauncherOne concept since late 2008, and as of 2015, is making it a larger part of Virgin's core business plan as the Virgin human spaceflight program has experienced multiple delays and a fatal accident in 2014.

In December 2012, DARPA announced that the Airborne Launch Assist Space Access program would provide the microsatellite rocket booster for the DARPA SeeMe program that intended to release a " constellation of 24 micro-satellites (~20 kg (44 lb) range) each with 1-m imaging resolution." The program was cancelled in December 2015.

In April 2013, Garvey Spacecraft was awarded a US$200,000 contract to evolve their Prospector 18 suborbital launch vehicle technology into an orbital nanosat launch vehicle capable of delivering a 10 kg (22 lb) payload into a 250 km (160 mi) orbit to an even-more-capable clustered "20/450 Nano/Micro Satellite Launch Vehicle" (NMSLV) capable of delivering 20 kg (44 lb) payloads into 450 km (280 mi) circular orbits.

The Boeing Small Launch Vehicle is an air-launched three-stage-to-orbit launch vehicle concept aimed to launch small payloads of 45 kg (100 lb) into low Earth orbit. The program is proposed to drive down launch costs for U.S. military small satellites to as low as US$300,000 per launch ($7,000/kg) and, if the development program was funded, as of 2012 could be operational by 2020.

The Swiss company Swiss Space Systems (S3) has announced plans in 2013 to develop a suborbital spaceplane named SOAR that would launch a microsat launch vehicle capable of putting a payload of up to 250 kg (550 lb) into low Earth orbit.

The Spanish company PLD Space born in 2011 with the objective of developing low cost launch vehicles called Miura 1 and Miura 5 with the capacity to place up to 150 kg (330 lb) into orbit.

The term "nanosatellite" or "nanosat" is applied to an artificial satellite with a wet mass between 1 and 10 kg (2.2 and 22.0 lb). Designs and proposed designs of these types may be launched individually, or they may have multiple nanosatellites working together or in formation, in which case, sometimes the term "satellite swarm" or " fractionated spacecraft" may be applied. Some designs require a larger "mother" satellite for communication with ground controllers or for launching and docking with nanosatellites. Over 1600 nanosatellites have been launched as of August 2021.

A CubeSat is a common type of nanosatellite, built in cube form based on multiples of 10 cm × 10 cm × 10 cm, with a mass of no more than 1.33 kilograms (2.9 lb) per unit. The CubeSat concept was first developed in 1999 by a collaborative team of California Polytechnic State University and Stanford University, and the specifications, for use by anyone planning to launch a CubeSat-style nanosatellite, are maintained by this group.

With continued advances in the miniaturization and capability increase of electronic technology and the use of satellite constellations, nanosatellites are increasingly capable of performing commercial missions that previously required microsatellites. For example, a 6U CubeSat standard has been proposed to enable a satellite constellation of thirty five 8 kg (18 lb) Earth-imaging satellites to replace a constellation of five 156 kg (344 lb) RapidEye Earth-imaging satellites, at the same mission cost, with significantly increased revisit times: every area of the globe can be imaged every 3.5 hours rather than the once per 24 hours with the RapidEye constellation. More rapid revisit times are a significant improvement for nations performing disaster response, which was the purpose of the RapidEye constellation. Additionally, the nanosat option would allow more nations to own their own satellite for off-peak (non-disaster) imaging data collection. As costs lower and production times shorten, nanosatellites are becoming increasingly feasible ventures for companies.

Example nanosatellites: ExoCube (CP-10), ArduSat, SPROUT

In the ten years of nanosat launches prior to 2014, only 75 nanosats were launched. Launch rates picked up substantially when in the three-month period from November 2013-January 2014 94 nanosats were launched.

One challenge of using nanosats has been the economic delivery of such small satellites to anywhere beyond low Earth orbit. By late 2014, proposals were being developed for larger spacecraft specifically designed to deliver swarms of nanosats to trajectories that are beyond Earth orbit for applications such as exploring distant asteroids.

With the emergence of the technological advances of miniaturization and increased capital to support private spaceflight initiatives in the 2010s, several startups have been formed to pursue opportunities with developing a variety of small-payload Nanosatellite Launch Vehicle (NLV) technologies.

NLVs proposed or under development include:

Actual NS launches:

ISRO launched 14 nanosatellites on 22 June 2016, 2 for Indian universities and 12 for the United States under the Flock-2P program. This launch was performed during the PSLV-C34 mission.

The term "picosatellite" or "picosat" (not to be confused with the PicoSAT series of microsatellites) is usually applied to artificial satellites with a wet mass between 0.1 and 1 kg (0.22 and 2.2 lb), although it is sometimes used to refer to any satellite that is under 1 kg in launch mass. Again, designs and proposed designs of these types usually have multiple picosatellites working together or in formation (sometimes the term "swarm" is applied). Some designs require a larger "mother" satellite for communication with ground controllers or for launching and docking with picosatellites.

Picosatellites are emerging as a new alternative for do-it-yourself kitbuilders. Picosatellites are currently commercially available across the full range of 0.1-1 kg (0.22-2.2 lb). Launch opportunities are now available for $12,000 to $18,000 for sub-1 kg picosat payloads that are approximately the size of a soda can.

The term "femtosatellite" or "femtosat" is usually applied to artificial satellites with a wet mass below 100 g (3.5 oz). Like picosatellites, some designs require a larger "mother" satellite for communication with ground controllers.

Three prototype "chip satellites" were launched to the ISS on Space Shuttle Endeavour on its final mission in May 2011. They were attached to the ISS external platform Materials International Space Station Experiment (MISSE-8) for testing. In April 2014, the nanosatellite KickSat was launched aboard a Falcon 9 rocket with the intention of releasing 104 femtosatellite-sized chipsats, or "Sprites". In the event, they were unable to complete the deployment on time due to a failure of an onboard clock and the deployment mechanism reentered the atmosphere on 14 May 2014, without having deployed any of the 5-gram femtosats. ThumbSat is another project intending to launch femtosatellites in the late 2010s. ThumbSat announced a launch agreement with CubeCat in 2017 to launch up to 1000 of the very small satellites.[needs update ]

In March 2019, the CubeSat KickSat-2 deployed 105 femtosats called "ChipSats" into Earth orbit. Each of the ChipSats weighed 4 grams. The satellites were tested for 3 days, and they then reentered the atmosphere and burned up.

Small satellites usually require innovative propulsion, attitude control, communication and computation systems.

Larger satellites usually use monopropellants or bipropellant combustion systems for propulsion and attitude control; these systems are complex and require a minimal amount of volume to surface area to dissipate heat. These systems may be used on larger small satellites, while other micro/nanosats have to use electric propulsion, compressed gas, vaporizable liquids such as butane or carbon dioxide or other innovative propulsion systems that are simple, cheap and scalable.

Small satellites can use conventional radio systems in UHF, VHF, S-band and X-band, although often miniaturized using more up-to-date technology as compared to larger satellites. Tiny satellites such as nanosats and small microsats may lack the power supply or mass for large conventional radio transponders, and various miniaturized or innovative communications systems have been proposed, such as laser receivers, antenna arrays and satellite-to-satellite communication networks. Few of these have been demonstrated in practice.

Electronics need to be rigorously tested and modified to be "space hardened" or resistant to the outer space environment (vacuum, microgravity, thermal extremes, and radiation exposure). Miniaturized satellites allow for the opportunity to test new hardware with reduced expense in testing. Furthermore, since the overall cost risk in the mission is much lower, more up-to-date but less space-proven technology can be incorporated into micro and nanosats than can be used in much larger, more expensive missions with less appetite for risk.

Small satellites are difficult to track with ground-based radar, so it is difficult to predict if they will collide with other satellites or human-occupied spacecraft. The U.S. Federal Communications Commission has rejected at least one small satellite launch request on these safety grounds.

1. "2014 Nano/Microsatellite Market Assessment" (PDF). annual market assessment series. Atlanta, Georgia: SEI. January 2014: 18. Archived (PDF) from the original on 22 February 2014.

2. Tristancho, Joshua; Gutierrez, Jordi (2010). "Implementation of a femto-satellite and a mini-launcher" (PDF). Universitat Politecnica de Catalunya: 3. Archived (PDF) from the original on 3 July 2013.

3. ^ Good, Andrew; Wendel, JoAnna (4 February 2019). "Beyond Mars, the Mini MarCO Spacecraft Fall Silent". Jet Propulsion Laboratory. NASA.

4. ^ EXCLUSIVE: Virgin Galactic unveils LauncherOne name! Archived 14 May 2013 at the Wayback Machine, Rob Coppinger, Flightglobal Hyperbola, 9 December 2008

5. ^ Burn-Callander, Rebecca (22 August 2015). "Virgin Galactic boldly goes into small satellites, telling future astronauts 'you have to wait'". UK Telegraph. Archived from the original on 24 August 2015.

6. ^ Lindsey, Clark (19 December 2012). "DARPA developing microsat constellation orbited with air-launch system". NewSpace Watch. Archived from the original on 26 May 2013.

7. ^ Verhoeven, C.J.M.; Bentum, M.J.; Monna, G.L.E.; Rotteveel, J.; Guo, J. (April-May 2011). "On the origin of satellite swarms" (PDF). Acta Astronautica. 68 (7-8): 1392-1395. Bibcode:2011AcAau..68.1392V. doi:10.1016/j.actaastro.2010.10.002.

8. CubeSat Design Specification Rev. 13 (PDF). The CubeSat Program (Report). California Polytechnic State University. 20 February 2014.

9. Tsitas, S. R.; Kingston, J. (February 2012). "6U CubeSat commercial applications". The Aeronautical Journal. 116 (1176): 189-198. doi:10.1017/S0001924000006692. S2CID 113099378.

10. "Nanosats are go!". Technology Quarterly Q2 2014. The Economist. 7 June 2014. Archived from the original on 12 June 2014. On November 19th Orbital Sciences, an American company, launched a rocket from the Wallops Flight Facility in Virginia. It carried 29 satellites aloft and released them into low-Earth orbit, a record for a single mission. Thirty hours later, Kosmotras, a Russian joint-venture, carried 32 satellites into a similar orbit. Then, in January 2014, Orbital Sciences carried 33 satellites up to the International Space Station (ISS), where they were cast off a month later.

11. ^ Lindsey, Clark (28 January 2013). "North Star rocket family with hybrid propulsion". NewSpace Watch. Archived from the original on 20 June 2013.

12. ^ "DIY Satellite Platforms". KK Technium. 9 November 2012. Archived from the original on 13 December 2012.

13. ^ Elizabeth Simpson (16 May 2011). "Chip satellites -- designed to blow in the solar wind -- depart on Endeavour's final launch". Cornell Chronicle. Archived from the original on 9 December 2012.

14. ^ "KickSat Nanosatellite Mission". European Space Agency. Archived from the original on 16 May 2014.

15. ^ https://www.bizjournals.com/prnewswire/press_releases/2017/07/24/SF48269

16. ^ "Stanford and NASA Ames researchers put inexpensive chip-size satellites into orbit". Stanford News. 3 June 2019.

# data[].attributes.attachment_link.description
A small satellite, miniaturized satellite, or smallsat is a satellite of low mass and size, usually under 1,200 kg (2,600 lb). While all such satellites can be referred to as "small", different classifications are used to categorize them based on mass.

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A minisatellite is a tract of repetitive DNA

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A minisatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from 10-60 base pairs) are typically repeated 5-50 times. Minisatellites occur at more than 1,000 locations in the human genome and they are notable for their high mutation rate and high diversity in the population. Minisatellites are prominent in the centromeres and telomeres of chromosomes, the latter protecting the chromosomes from damage. The name "satellite" refers to the early observation that centrifugation of genomic DNA in a test tube separates a prominent layer of bulk DNA from accompanying "satellite" layers of repetitive DNA. Minisatellites are small sequences of DNA that do not encode proteins but appear throughout the genome hundreds of times, with many repeated copies lying next to each other.

Minisatellites and their shorter cousins, the microsatellites, together are classified as VNTR (variable number of tandem repeats) DNA. Confusingly, minisatellites are often referred to as VNTRs, and microsatellites are often referred to as short tandem repeats (STRs) or simple sequence repeats (SSRs).

Minisatellites consist of repetitive, generally GC-rich, motifs that range in length from 10 to over 100 base pairs. These variant repeats are tandemly intermingled. Some minisatellites contain a central sequence (or "core unit") of nucleobases "GGGCAGGANG" (where N can be any base) or more generally consist of sequence motifs of purines ( Adenine (A) and Guanine (G)) and pyrimidines ( Cytosine (C) and Thymine (T)).

Hypervariable minisatellites have core units 9-64 bp long and are found mainly at the centromeric regions.

In humans, 90% of minisatellites are found at the sub-telomeric region of chromosomes. The human telomere sequence itself is a tandem repeat: TTAGGG TTAGGG TTAGGG ...

Minisatellites have been implicated as regulators of gene expression (e.g. at levels of transcription, alternative splicing, or imprint control). They are generally non-coding DNA but sometimes are part of possible genes.

Minisatellites also constitute the chromosomal telomeres, which protect the ends of a chromosome from deterioration or from fusion with neighbouring chromosomes.

Minisatellites have been associated with chromosome fragile sites and are proximal to a number of recurrent translocation breakpoints.

Some human minisatellites (~1%) have been demonstrated to be hypermutable, with an average mutation rate in the germline higher than 0.5% up to over 20%, making them the most unstable region in the human genome known to date. While other genomes (mouse, rat and pig) contain minisatellite-like sequences, none was found to be hypermutable. Since all hypermutable minisatellites contain internal variants, they provide extremely informative systems for analyzing the complex turnover processes that occur at this class of tandem repeat. Minisatellite variant repeat mapping by PCR (MVR-PCR) has been extensively used to chart the interspersion patterns of variant repeats along the array, which provides details on the structure of the alleles before and after mutation.

Studies have revealed distinct mutation processes operating in somatic and germline cells. Somatic instability detected in blood DNA shows simple and rare intra-allelic events two to three orders of magnitude lower than in sperm. In contrast, complex inter-allelic conversion-like events occur in the germline.

Additional analyses of DNA sequences flanking human minisatellites have also revealed an intense and highly localized meiotic crossover hotspot that is centered upstream of the unstable side of minisatellite arrays. Repeat turnover therefore appears to be controlled by recombinational activity in DNA that flanks the repeat array and results in a polarity of mutation. These findings have suggested that minisatellites most probably evolved as bystanders of localized meiotic recombination hotspots in the human genome.

It has been proposed that minisatellite sequences encourage chromosomes to swap DNA. In alternative models, it is the presence of neighbouring double-strand hotspots which is the primary cause of minisatellite repeat copy number variations. Somatic changes are suggested to result from replication difficulties (which might include replication slippage, among other phenomena).

Studies have shown that the evolutionary fate of minisatellites tends towards an equilibrium distribution in the size of alleles, until mutations in the flanking DNA affect the recombinational activity of a minisatellite by suppressing DNA instability. Such an event would ultimately lead to the extinction of a hypermutable minisatellite by meiotic drive.

The first human minisatellite was discovered in 1980 by A.R. Wyman and R. White,. Discovering their high level of variability, Sir Alec Jeffreys developed DNA fingerprinting based on minisatellites, solving the first immigration case by DNA in 1985, and the first forensic murder case, the Enderby murders in the United Kingdom, in 1986. Minisatellites were subsequently also used for genetic markers in linkage analysis and population studies, but were soon replaced by microsatellite profiling in the 1990s.

The term satellite DNA originates from the observation in the 1960s of a fraction of sheared DNA that showed a distinct buoyant density, detectable as a 'satellite peak' in density gradient centrifugation, and that was subsequently identified as large centromeric tandem repeats. When shorter (10-30-bp) tandem repeats were later identified, they came to be known as minisatellites. Finally, with the discovery of tandem iterations of simple sequence motifs, the term microsatellites was coined.

1. ^ Minisatellite at the US National Library of Medicine Medical Subject Headings (MeSH)

2. ^ Tawn, E. Janet; Rees, Gwen S.; Leith, Cheryl; Winther, Jeanette F.; Curwen, Gillian B.; Stovall, Marilyn; Olsen, Jørgen H.; Rechnitzer, Catherine; Schroeder, Henrik; Guldberg, Per; Boice, John D. (March 2011). "Germline minisatellite mutations in survivors of childhood and young adult cancer treated with radiation". International Journal of Radiation Biology. 87 (3): 330-340. doi:10.3109/09553002.2011.530338. ISSN 0955-3002. PMC . PMID 21087171.

3. ^ Turnpenny, P. & Ellard, S. (2005). Emery's Elements of Medical Genetics, 12th. ed. Elsevier, London.

4. ^ Jangampalli Adi, Pradeep Kiran (May 2011). "Comparison and correlation of Simple Sequence Repeats distribution in genomes of Brucella species". Bioinformation. 6 (5): 179-182. doi:10.6026/97320630006179. PMC . PMID 21738309.

5. ^ Wyman AR, White R (November 1980). "A highly polymorphic locus in human DNA". Proceedings of the National Academy of Sciences of the United States of America. 77 (11): 6754-8. Bibcode:1980PNAS...77.6754W. doi:10.1073/pnas.77.11.6754. PMC . PMID 6935681.

6. ^ Jeffreys AJ, Wilson V, Thein SL (March 1985). "Hypervariable 'minisatellite' regions in human DNA". Nature. 314 (6006): 67-73. Bibcode:1985Natur.314...67J. doi:10.1038/314067a0. PMID 3856104. S2CID 4356170.

# data[].attributes.attachment_link.description
A minisatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from 10-60 base pairs) are typically repeated 5-50 times. Minisatellites occur at more than 1,000 locations in the human genome and they are notable for their high mutation rate and high diversity in the population.

# data[].attributes.body
The word chromosome (/ˈkroʊməˌsoʊm, -ˌzoʊm/[7][8]) comes from the Greek χρῶμα (chroma, "colour") and σῶμα (soma, "body"), describing their strong staining by particular dyes.

A single-nucleotide polymorphism in the OR5A1 receptor (rs6591536[7]) causes very significant differences in the odor perception of beta-ionone. Individuals who contain at least one G allele are sensitive to beta-ionone and perceive a pleasant floral scent, while individuals who are homozygous AA are ~100 times less sensitive and at higher concentrations perceive a pungent sour/vinegar odor instead.

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Some use the term chromosome in a wider sense, to refer to the individualized portions of chromatin in cells, either visible or not under light microscopy. Others use the concept in a narrower sense, to refer to the individualized portions of chromatin during cell division, visible under light microscopy due to high condensation.

# data[].attributes.body
References to violets and the desirable nature of the fragrance go back to classical sources such as Pliny and Horace when the name ‘Ion’ was in use to describe this flower from which the name of the distinctive chemical constituents of the flower, the ionones – is derived.

The combination of α-ionone and β-ionone is characteristic of the scent of violets and used with other components in perfumery and flavouring to recreate their scent.

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( Carl Linnaeus (;[1][2] 23 May 1707 - 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné[3] ( Swedish pronunciation: [ˈkɑːɭ fɔn lɪˈneː] listen )), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the modern system of naming organisms. He is known as the "father of modern taxonomy".[4] Many of his writings were in Latin; his name is rendered in Latin as Carolus Linnæus and, after his 1761 ennoblement, as Carolus a Linné .

Linnaeus was born in Råshult, the countryside of Småland, in southern Sweden. He received most of his higher education at Uppsala University and began giving lectures in botany there in 1730. He lived abroad between 1735 and 1738, where he studied and also published the first edition of his in the Netherlands. He then returned to Sweden where he became professor of medicine and botany at Uppsala. In the 1740s, he was sent on several journeys through Sweden to find and classify plants and animals. In the 1750s and 1760s, he continued to collect and classify animals, plants, and minerals, while publishing several volumes. He was one of the most acclaimed scientists in Europe at the time of his death.

Philosopher Jean-Jacques Rousseau sent him the message: "Tell him I know no greater man on earth." Johann Wolfgang von Goethe wrote: "With the exception of Shakespeare and Spinoza, I know no one among the no longer living who has influenced me more strongly." Swedish author August Strindberg wrote: "Linnaeus was in reality a poet who happened to become a naturalist." Linnaeus has been called (Prince of Botanists) and "The Pliny of the North". He is also considered one of the founders of modern ecology.

In botany and zoology, the abbreviation L. is used to indicate Linnaeus as the authority for a species' name. In older publications, the abbreviation "Linn." is found. Linnaeus's remains constitute the type specimen for the species Homo sapiens following the International Code of Zoological Nomenclature, since the sole specimen that he is known to have examined was himself.

Linnaeus was born in the village of Råshult in Småland, Sweden, on 23 May 1707. He was the first child of Nicolaus (Nils) Ingemarsson (who later adopted the family name Linnaeus) and Christina Brodersonia. His siblings were Anna Maria Linnæa, Sofia Juliana Linnæa, Samuel Linnæus (who would eventually succeed their father as rector of Stenbrohult and write a manual on beekeeping), and Emerentia Linnæa. His father taught him Latin as a small child.

One of a long line of peasants and priests, Nils was an amateur botanist, a Lutheran minister, and the curate of the small village of Stenbrohult in Småland. Christina was the daughter of the rector of Stenbrohult, Samuel Brodersonius.

Even in his early years, Linnaeus seemed to have a liking for plants, flowers in particular. Whenever he was upset, he was given a flower, which immediately calmed him. Nils spent much time in his garden and often showed flowers to Linnaeus and told him their names. Soon Linnaeus was given his own patch of earth where he could grow plants.

Carl's father was the first in his ancestry to adopt a permanent surname. Before that, ancestors had used the patronymic naming system of Scandinavian countries: his father was named Ingemarsson after his father Ingemar Bengtsson. When Nils was admitted to the University of Lund, he had to take on a family name. He adopted the Latinate name Linnæus after a giant linden tree (or lime tree), in Swedish, that grew on the family homestead. This name was spelled with the æ ligature. When Carl was born, he was named Carl Linnæus, with his father's family name. The son also always spelled it with the æ ligature, both in handwritten documents and in publications. Carl's patronymic would have been Nilsson, as in Carl Nilsson Linnæus.

Early education

Linnaeus's father began teaching him basic Latin, religion, and geography at an early age. When Linnaeus was seven, Nils decided to hire a tutor for him. The parents picked Johan Telander, a son of a local yeoman. Linnaeus did not like him, writing in his autobiography that Telander "was better calculated to extinguish a child's talents than develop them".

Two years after his tutoring had begun, he was sent to the Lower Grammar School at Växjö in 1717. Linnaeus rarely studied, often going to the countryside to look for plants. At some point, his father went to visit him and, after hearing critical assessements by his preceptors, he decided to put the youth as an apprentice to some honest cobbler. He reached the last year of the Lower School when he was fifteen, which was taught by the headmaster, Daniel Lannerus, who was interested in botany. Lannerus noticed Linnaeus's interest in botany and gave him the run of his garden.

He also introduced him to Johan Rothman, the state doctor of Småland and a teacher at Katedralskolan (a gymnasium) in Växjö. Also a botanist, Rothman broadened Linnaeus's interest in botany and helped him develop an interest in medicine. By the age of 17, Linnaeus had become well acquainted with the existing botanical literature. He remarks in his journal that he "read day and night, knowing like the back of my hand, Arvidh Månsson's Rydaholm Book of Herbs, Tillandz's Flora Åboensis, Palmberg's Serta Florea Suecana, Bromelii's Chloros Gothica and Rudbeckii's Hortus Upsaliensis".

Linnaeus entered the Växjö Katedralskola in 1724, where he studied mainly Greek, Hebrew, theology and mathematics, a curriculum designed for boys preparing for the priesthood. In the last year at the gymnasium, Linnaeus's father visited to ask the professors how his son's studies were progressing; to his dismay, most said that the boy would never become a scholar. Rothman believed otherwise, suggesting Linnaeus could have a future in medicine. The doctor offered to have Linnaeus live with his family in Växjö and to teach him physiology and botany. Nils accepted this offer.

University studies

Rothman showed Linnaeus that botany was a serious subject. He taught Linnaeus to classify plants according to Tournefort's system. Linnaeus was also taught about the sexual reproduction of plants, according to Sébastien Vaillant. In 1727, Linnaeus, age 21, enrolled in Lund University in Skåne. He was registered as , the Latin form of his full name, which he also used later for his Latin publications.

Professor Kilian Stobæus, natural scientist, physician and historian, offered Linnaeus tutoring and lodging, as well as the use of his library, which included many books about botany. He also gave the student free admission to his lectures. In his spare time, Linnaeus explored the flora of Skåne, together with students sharing the same interests.

In August 1728, Linnaeus decided to attend Uppsala University on the advice of Rothman, who believed it would be a better choice if Linnaeus wanted to study both medicine and botany. Rothman based this recommendation on the two professors who taught at the medical faculty at Uppsala: Olof Rudbeck the Younger and Lars Roberg. Although Rudbeck and Roberg had undoubtedly been good professors, by then they were older and not so interested in teaching. Rudbeck no longer gave public lectures, and had others stand in for him. The botany, zoology, pharmacology and anatomy lectures were not in their best state. In Uppsala, Linnaeus met a new benefactor, Olof Celsius, who was a professor of theology and an amateur botanist. He received Linnaeus into his home and allowed him use of his library, which was one of the richest botanical libraries in Sweden.

In 1729, Linnaeus wrote a thesis, Praeludia Sponsaliorum Plantarum on plant sexual reproduction. This attracted the attention of Rudbeck; in May 1730, he selected Linnaeus to give lectures at the University although the young man was only a second-year student. His lectures were popular, and Linnaeus often addressed an audience of 300 people. In June, Linnaeus moved from Celsius's house to Rudbeck's to become the tutor of the three youngest of his 24 children. His friendship with Celsius did not wane and they continued their botanical expeditions. Over that winter, Linnaeus began to doubt Tournefort's system of classification and decided to create one of his own. His plan was to divide the plants by the number of stamens and pistils. He began writing several books, which would later result in, for example, and . He also produced a book on the plants grown in the Uppsala Botanical Garden, .

Expedition to Lapland

During a visit with his parents, Linnaeus told them about his plan to travel to Lapland; Rudbeck had made the journey in 1695, but the detailed results of his exploration were lost in a fire seven years afterwards. Linnaeus's hope was to find new plants, animals and possibly valuable minerals. He was also curious about the customs of the native Sami people, reindeer-herding nomads who wandered Scandinavia's vast tundras. In April 1732, Linnaeus was awarded a grant from the Royal Society of Sciences in Uppsala for his journey.

Linnaeus began his expedition from Uppsala on 12 May 1732, just before he turned 25. He travelled on foot and horse, bringing with him his journal, botanical and ornithological manuscripts and sheets of paper for pressing plants. Near Gävle he found great quantities of Campanula serpyllifolia, later known as Linnaea borealis, the twinflower that would become his favourite. He sometimes dismounted on the way to examine a flower or rock and was particularly interested in mosses and lichens, the latter a main part of the diet of the reindeer, a common and economically important animal in Lapland.

Linnaeus travelled clockwise around the coast of the Gulf of Bothnia, making major inland incursions from Umeå, Luleå and Tornio. He returned from his six-month-long, over 2,000 kilometres (1,200 mi) expedition in October, having gathered and observed many plants, birds and rocks. Although Lapland was a region with limited biodiversity, Linnaeus described about 100 previously unidentified plants. These became the basis of his book . However, on the expedition to Lapland, Linnaeus used Latin names to describe organisms because he had not yet developed the binomial system.

In Linnaeus's ideas about nomenclature and classification were first used in a practical way, making this the first proto-modern Flora. The account covered 534 species, used the Linnaean classification system and included, for the described species, geographical distribution and taxonomic notes. It was Augustin Pyramus de Candolle who attributed Linnaeus with as the first example in the botanical genre of Flora writing. Botanical historian E. L. Greene described as "the most classic and delightful" of Linnaeus's works.

It was also during this expedition that Linnaeus had a flash of insight regarding the classification of mammals. Upon observing the lower jawbone of a horse at the side of a road he was travelling, Linnaeus remarked: "If I only knew how many teeth and of what kind every animal had, how many teats and where they were placed, I should perhaps be able to work out a perfectly natural system for the arrangement of all quadrupeds."

In 1734, Linnaeus led a small group of students to Dalarna. Funded by the Governor of Dalarna, the expedition was to catalogue known natural resources and discover new ones, but also to gather intelligence on Norwegian mining activities at Røros.

Years in the Dutch Republic (1735-38)

His relations with Nils Rosén having worsened, Linnaeus accepted an invitation from Claes Sohlberg, son of a mining inspector, to spend the Christmas holiday in Falun, where Linnaeus was permitted to visit the mines.

In April 1735, at the suggestion of Sohlberg's father, Linnaeus and Sohlberg set out for the Dutch Republic, where Linnaeus intended to study medicine at the University of Harderwijk while tutoring Sohlberg in exchange for an annual salary. At the time, it was common for Swedes to pursue doctoral degrees in the Netherlands, then a highly revered place to study natural history.

On the way, the pair stopped in Hamburg, where they met the mayor, who proudly showed them a supposed wonder of nature in his possession: the taxidermied remains of a seven-headed hydra. Linnaeus quickly discovered the specimen was a fake, cobbled together from the jaws and paws of weasels and the skins of snakes. The provenance of the hydra suggested to Linnaeus that it had been manufactured by monks to represent the Beast of Revelation. Even at the risk of incurring the mayor's wrath, Linnaeus made his observations public, dashing the mayor's dreams of selling the hydra for an enormous sum. Linnaeus and Sohlberg were forced to flee from Hamburg.

Linnaeus began working towards his degree as soon as he reached Harderwijk, a university known for awarding degrees in as little as a week. He submitted a dissertation, written back in Sweden, entitled Dissertatio medica inauguralis in qua exhibetur hypothesis nova de febrium intermittentium causa, in which he laid out his hypothesis that malaria arose only in areas with clay-rich soils. Although he failed to identify the true source of disease transmission, (i.e., the mosquito), he did correctly predict that Artemisia annua ( wormwood) would become a source of antimalarial medications.

Within two weeks he had completed his oral and practical examinations and was awarded a doctoral degree.

That summer Linnaeus reunited with Peter Artedi, a friend from Uppsala with whom he had once made a pact that should either of the two predecease the other, the survivor would finish the decedent's work. Ten weeks later, Artedi drowned in the canals of Amsterdam, leaving behind an unfinished manuscript on the classification of fish.

One of the first scientists Linnaeus met in the Netherlands was Johan Frederik Gronovius, to whom Linnaeus showed one of the several manuscripts he had brought with him from Sweden. The manuscript described a new system for classifying plants. When Gronovius saw it, he was very impressed, and offered to help pay for the printing. With an additional monetary contribution by the Scottish doctor Isaac Lawson, the manuscript was published as (1735).

Linnaeus became acquainted with one of the most respected physicians and botanists in the Netherlands, Herman Boerhaave, who tried to convince Linnaeus to make a career there. Boerhaave offered him a journey to South Africa and America, but Linnaeus declined, stating he would not stand the heat. Instead, Boerhaave convinced Linnaeus that he should visit the botanist Johannes Burman. After his visit, Burman, impressed with his guest's knowledge, decided Linnaeus should stay with him during the winter. During his stay, Linnaeus helped Burman with his . Burman also helped Linnaeus with the books on which he was working: and .

George Clifford, Philip Miller, and Johann Jacob Dillenius

In August 1735, during Linnaeus's stay with Burman, he met George Clifford III, a director of the Dutch East India Company and the owner of a rich botanical garden at the estate of Hartekamp in Heemstede. Clifford was very impressed with Linnaeus's ability to classify plants, and invited him to become his physician and superintendent of his garden. Linnaeus had already agreed to stay with Burman over the winter, and could thus not accept immediately. However, Clifford offered to compensate Burman by offering him a copy of Sir Hans Sloane's Natural History of Jamaica, a rare book, if he let Linnaeus stay with him, and Burman accepted. On 24 September 1735, Linnaeus moved to Hartekamp to become personal physician to Clifford, and curator of Clifford's herbarium. He was paid 1,000 florins a year, with free board and lodging. Though the agreement was only for a winter of that year, Linnaeus practically stayed there until 1738. It was here that he wrote a book Hortus Cliffortianus, in the preface of which he described his experience as "the happiest time of my life". (A portion of Hartekamp was declared as public garden in April 1956 by the Heemstede local authority, and was named "Linnaeushof". It eventually became, as it is claimed, the biggest playground in Europe.)

In July 1736, Linnaeus travelled to England, at Clifford's expense. He went to London to visit Sir Hans Sloane, a collector of natural history, and to see his cabinet, as well as to visit the Chelsea Physic Garden and its keeper, Philip Miller. He taught Miller about his new system of subdividing plants, as described in . Miller was in fact reluctant to use the new binomial nomenclature, preferring the classifications of Joseph Pitton de Tournefort and John Ray at first. Linnaeus, nevertheless, applauded Miller's Gardeners Dictionary, The conservative Scot actually retained in his dictionary a number of pre-Linnaean binomial signifiers discarded by Linnaeus but which have been retained by modern botanists. He only fully changed to the Linnaean system in the edition of The Gardeners Dictionary of 1768. Miller ultimately was impressed, and from then on started to arrange the garden according to Linnaeus's system.

Linnaeus also travelled to Oxford University to visit the botanist Johann Jacob Dillenius. He failed to make Dillenius publicly fully accept his new classification system, though the two men remained in correspondence for many years afterwards. Linnaeus dedicated his Critica Botanica to him, as " opus botanicum quo absolutius mundus non-vidit". Linnaeus would later name a genus of tropical tree Dillenia in his honour. He then returned to Hartekamp, bringing with him many specimens of rare plants. The next year, 1737, he published , in which he described 935 genera of plants, and shortly thereafter he supplemented it with Corollarium Generum Plantarum , with another sixty ( sexaginta) genera.

His work at Hartekamp led to another book, , a catalogue of the botanical holdings in the herbarium and botanical garden of Hartekamp. He wrote it in nine months (completed in July 1737), but it was not published until 1738. It contains the first use of the name , which Linnaeus used to describe a genus of pitcher plants.

Return to Sweden

When Linnaeus returned to Sweden on 28 June 1738, he went to Falun, where he entered into an engagement to Sara Elisabeth Moræa. Three months later, he moved to Stockholm to find employment as a physician, and thus to make it possible to support a family. Once again, Linnaeus found a patron; he became acquainted with Count Carl Gustav Tessin, who helped him get work as a physician at the Admiralty. During this time in Stockholm, Linnaeus helped found the Royal Swedish Academy of Science; he became the first Praeses of the academy by drawing of lots.

Because his finances had improved and were now sufficient to support a family, he received permission to marry his fiancée, Sara Elisabeth Moræa. Their wedding was held 26 June 1739. Seventeen months later, Sara gave birth to their first son, Carl. Two years later, a daughter, Elisabeth Christina, was born, and the subsequent year Sara gave birth to Sara Magdalena, who died when 15 days old. Sara and Linnaeus would later have four other children: Lovisa, Sara Christina, Johannes and Sophia.

In May 1741, Linnaeus was appointed Professor of Medicine at Uppsala University, first with responsibility for medicine-related matters. Soon, he changed place with the other Professor of Medicine, Nils Rosén, and thus was responsible for the Botanical Garden (which he would thoroughly reconstruct and expand), botany and natural history, instead. In October that same year, his wife and nine-month-old son followed him to live in Uppsala.

Öland and Gotland

Ten days after he was appointed Professor, he undertook an expedition to the island provinces of Öland and Gotland with six students from the university, to look for plants useful in medicine. First, they travelled to Öland and stayed there until 21 June, when they sailed to Visby in Gotland. Linnaeus and the students stayed on Gotland for about a month, and then returned to Uppsala. During this expedition, they found 100 previously unrecorded plants. The observations from the expedition were later published in Öländska och Gothländska Resa , written in Swedish. Like , it contained both zoological and botanical observations, as well as observations concerning the culture in Öland and Gotland.

During the summer of 1745, Linnaeus published two more books: and . was a strictly botanical book, while was zoological. Anders Celsius had created the temperature scale named after him in 1742. Celsius's scale was inverted compared to today, the boiling point at 0 °C and freezing point at 100 °C. In 1745, Linnaeus inverted the scale to its present standard.

Västergötland

In the summer of 1746, Linnaeus was once again commissioned by the Government to carry out an expedition, this time to the Swedish province of Västergötland. He set out from Uppsala on 12 June and returned on 11 August. On the expedition his primary companion was Erik Gustaf Lidbeck, a student who had accompanied him on his previous journey. Linnaeus described his findings from the expedition in the book , published the next year. After he returned from the journey, the Government decided Linnaeus should take on another expedition to the southernmost province Scania. This journey was postponed, as Linnaeus felt too busy.

In 1747, Linnaeus was given the title archiater, or chief physician, by the Swedish king Adolf Frederick-a mark of great respect. The same year he was elected member of the Academy of Sciences in Berlin.

In the spring of 1749, Linnaeus could finally journey to Scania, again commissioned by the Government. With him he brought his student, Olof Söderberg. On the way to Scania, he made his last visit to his brothers and sisters in Stenbrohult since his father had died the previous year. The expedition was similar to the previous journeys in most aspects, but this time he was also ordered to find the best place to grow walnut and Swedish whitebeam trees; these trees were used by the military to make rifles. While there, they also visited the Ramlösa mineral spa, where he remarked on the quality of its ferruginous water. The journey was successful, and Linnaeus's observations were published the next year in .

Rector of Uppsala University

In 1750, Linnaeus became rector of Uppsala University, starting a period where natural sciences were esteemed. Perhaps the most important contribution he made during his time at Uppsala was to teach; many of his students travelled to various places in the world to collect botanical samples. Linnaeus called the best of these students his "apostles". His lectures were normally very popular and were often held in the Botanical Garden. He tried to teach the students to think for themselves and not trust anybody, not even him. Even more popular than the lectures were the botanical excursions made every Saturday during summer, where Linnaeus and his students explored the flora and fauna in the vicinity of Uppsala.

Linnaeus published Philosophia Botanica in 1751. The book contained a complete survey of the taxonomy system he had been using in his earlier works. It also contained information of how to keep a journal on travels and how to maintain a botanical garden.

During Linnaeus's time it was normal for upper class women to have wet nurses for their babies. Linnaeus joined an ongoing campaign to end this practice in Sweden and promote breast-feeding by mothers. In 1752 Linnaeus published a thesis along with Frederick Lindberg, a physician student, based on their experiences. In the tradition of the period, this dissertation was essentially an idea of the presiding reviewer ( prases) expounded upon by the student. Linnaeus's dissertation was translated into French by J.E. Gilibert in 1770 as La Nourrice marâtre, ou Dissertation sur les suites funestes du nourrisage mercénaire. Linnaeus suggested that children might absorb the personality of their wet nurse through the milk. He admired the child care practices of the Lapps and pointed out how healthy their babies were compared to those of Europeans who employed wet nurses. He compared the behaviour of wild animals and pointed out how none of them denied their newborns their breastmilk. It is thought that his activism played a role in his choice of the term Mammalia for the class of organisms.

Linnaeus published Species Plantarum, the work which is now internationally accepted as the starting point of modern botanical nomenclature, in 1753. The first volume was issued on 24 May, the second volume followed on 16 August of the same year. The book contained 1,200 pages and was published in two volumes; it described over 7,300 species. The same year the king dubbed him knight of the Order of the Polar Star, the first civilian in Sweden to become a knight in this order. He was then seldom seen not wearing the order's insignia.

Ennoblement

Linnaeus felt Uppsala was too noisy and unhealthy, so he bought two farms in 1758: Hammarby and Sävja. The next year, he bought a neighbouring farm, Edeby. He spent the summers with his family at Hammarby; initially it only had a small one-storey house, but in 1762 a new, larger main building was added. In Hammarby, Linnaeus made a garden where he could grow plants that could not be grown in the Botanical Garden in Uppsala. He began constructing a museum on a hill behind Hammarby in 1766, where he moved his library and collection of plants. A fire that destroyed about one third of Uppsala and had threatened his residence there necessitated the move.

Since the initial release of in 1735, the book had been expanded and reprinted several times; the tenth edition was released in 1758. This edition established itself as the starting point for zoological nomenclature, the equivalent of .

The Swedish King Adolf Frederick granted Linnaeus nobility in 1757, but he was not ennobled until 1761. With his ennoblement, he took the name Carl von Linné (Latinised as ), 'Linné' being a shortened and gallicised version of 'Linnæus', and the German nobiliary particle ' von' signifying his ennoblement. The noble family's coat of arms prominently features a twinflower, one of Linnaeus's favourite plants; it was given the scientific name Linnaea borealis in his honour by Gronovius. The shield in the coat of arms is divided into thirds: red, black and green for the three kingdoms of nature (animal, mineral and vegetable) in Linnaean classification; in the centre is an egg "to denote Nature, which is continued and perpetuated in ovo." At the bottom is a phrase in Latin, borrowed from the Aeneid, which reads " Famam extendere factis": we extend our fame by our deeds. Linnaeus inscribed this personal motto in books that were given to him by friends.

After his ennoblement, Linnaeus continued teaching and writing. His reputation had spread over the world, and he corresponded with many different people. For example, Catherine II of Russia sent him seeds from her country. He also corresponded with Giovanni Antonio Scopoli, "the Linnaeus of the Austrian Empire", who was a doctor and a botanist in Idrija, Duchy of Carniola (nowadays Slovenia). Scopoli communicated all of his research, findings, and descriptions (for example of the olm and the dormouse, two little animals hitherto unknown to Linnaeus). Linnaeus greatly respected Scopoli and showed great interest in his work. He named a solanaceous genus, , the source of scopolamine, after him, but because of the great distance between them, they never met.

Final years

Linnaeus was relieved of his duties in the Royal Swedish Academy of Science in 1763, but continued his work there as usual for more than ten years after. In 1769 he was elected to the American Philosophical Society for his work. He stepped down as rector at Uppsala University in December 1772, mostly due to his declining health.

Linnaeus's last years were troubled by illness. He had had a disease called the Uppsala fever in 1764, but survived due to the care of Rosén. He developed sciatica in 1773, and the next year, he had a stroke which partially paralysed him. He had a second stroke in 1776, losing the use of his right side and leaving him bereft of his memory; while still able to admire his own writings, he could not recognise himself as their author.

In December 1777, he had another stroke which greatly weakened him, and eventually led to his death on 10 January 1778 in Hammarby. Despite his desire to be buried in Hammarby, he was buried in Uppsala Cathedral on 22 January.

His library and collections were left to his widow Sara and their children. Joseph Banks, an eminent botanist, wished to purchase the collection, but his son Carl refused the offer and instead moved the collection to Uppsala. In 1783 Carl died and Sara inherited the collection, having outlived both her husband and son. She tried to sell it to Banks, but he was no longer interested; instead an acquaintance of his agreed to buy the collection. The acquaintance was a 24-year-old medical student, James Edward Smith, who bought the whole collection: 14,000 plants, 3,198 insects, 1,564 shells, about 3,000 letters and 1,600 books. Smith founded the Linnean Society of London five years later.

The von Linné name ended with his son Carl, who never married. His other son, Johannes, had died aged 3. There are over two hundred descendants of Linnaeus through two of his daughters.

During Linnaeus's time as Professor and Rector of Uppsala University, he taught many devoted students, 17 of whom he called "apostles". They were the most promising, most committed students, and all of them made botanical expeditions to various places in the world, often with his help. The amount of this help varied; sometimes he used his influence as Rector to grant his apostles a scholarship or a place on an expedition. To most of the apostles he gave instructions of what to look for on their journeys. Abroad, the apostles collected and organised new plants, animals and minerals according to Linnaeus's system. Most of them also gave some of their collection to Linnaeus when their journey was finished. Thanks to these students, the Linnaean system of taxonomy spread through the world without Linnaeus ever having to travel outside Sweden after his return from Holland. The British botanist William T. Stearn notes, without Linnaeus's new system, it would not have been possible for the apostles to collect and organise so many new specimens. Many of the apostles died during their expeditions.

Early expeditions

Christopher Tärnström, the first apostle and a 43-year-old pastor with a wife and children, made his journey in 1746. He boarded a Swedish East India Company ship headed for China. Tärnström never reached his destination, dying of a tropical fever on Côn Sơn Island the same year. Tärnström's widow blamed Linnaeus for making her children fatherless, causing Linnaeus to prefer sending out younger, unmarried students after Tärnström. Six other apostles later died on their expeditions, including Pehr Forsskål and Pehr Löfling.

Two years after Tärnström's expedition, Finnish-born Pehr Kalm set out as the second apostle to North America. There he spent two-and-a-half years studying the flora and fauna of Pennsylvania, New York, New Jersey and Canada. Linnaeus was overjoyed when Kalm returned, bringing back with him many pressed flowers and seeds. At least 90 of the 700 North American species described in Species Plantarum had been brought back by Kalm.

Cook expeditions and Japan

Daniel Solander was living in Linnaeus's house during his time as a student in Uppsala. Linnaeus was very fond of him, promising Solander his eldest daughter's hand in marriage. On Linnaeus's recommendation, Solander travelled to England in 1760, where he met the English botanist Joseph Banks. With Banks, Solander joined James Cook on his expedition to Oceania on the in 1768-71. Solander was not the only apostle to journey with James Cook; Anders Sparrman followed on the Resolution in 1772-75 bound for, among other places, Oceania and South America. Sparrman made many other expeditions, one of them to South Africa.

Perhaps the most famous and successful apostle was Carl Peter Thunberg, who embarked on a nine-year expedition in 1770. He stayed in South Africa for three years, then travelled to Japan. All foreigners in Japan were forced to stay on the island of Dejima outside Nagasaki, so it was thus hard for Thunberg to study the flora. He did, however, manage to persuade some of the translators to bring him different plants, and he also found plants in the gardens of Dejima. He returned to Sweden in 1779, one year after Linnaeus's death.

Major publications

The first edition of was printed in the Netherlands in 1735. It was a twelve-page work. By the time it reached its 10th edition in 1758, it classified 4,400 species of animals and 7,700 species of plants. People from all over the world sent their specimens to Linnaeus to be included. By the time he started work on the 12th edition, Linnaeus needed a new invention-the index card -to track classifications.

In Systema Naturae, the unwieldy names mostly used at the time, such as "Physalis annua ramosissima, ramis angulosis glabris, foliis dentato-serratis ", were supplemented with concise and now familiar "binomials", composed of the generic name, followed by a specific epithet-in the case given, Physalis angulata. These binomials could serve as a label to refer to the species. Higher taxa were constructed and arranged in a simple and orderly manner. Although the system, now known as binomial nomenclature, was partially developed by the Bauhin brothers (see Gaspard Bauhin and Johann Bauhin) almost 200 years earlier, Linnaeus was the first to use it consistently throughout the work, including in monospecific genera, and may be said to have popularised it within the scientific community.

After the decline in Linnaeus's health in the early 1770s, publication of editions of Systema Naturae went in two different directions. Another Swedish scientist, Johan Andreas Murray issued the Regnum Vegetabile section separately in 1774 as the Systema Vegetabilium, rather confusingly labelled the 13th edition. Meanwhile, a 13th edition of the entire Systema appeared in parts between 1788 and 1793. It was through the Systema Vegetabilium that Linnaeus's work became widely known in England, following its translation from the Latin by the Lichfield Botanical Society as A System of Vegetables (1783-1785).

Orbis eruditi judicium de Caroli Linnaei MD scriptis

('Opinion of the learned world on the writings of Carl Linnaeus, Doctor') Published in 1740, this small octavo-sized pamphlet was presented to the State Library of New South Wales by the Linnean Society of NSW in 2018. This is considered among the rarest of all the writings of Linnaeus, and crucial to his career, securing him his appointment to a professorship of medicine at Uppsala University. From this position he laid the groundwork for his radical new theory of classifying and naming organisms for which he was considered the founder of modern taxonomy.

(or, more fully, Species Plantarum, exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas ) was first published in 1753, as a two-volume work. Its prime importance is perhaps that it is the primary starting point of plant nomenclature as it exists today.

Genera plantarum: eorumque characteres naturales secundum numerum, figuram, situm, et proportionem omnium fructificationis partium was first published in 1737, delineating plant genera. Around 10 editions were published, not all of them by Linnaeus himself; the most important is the 1754 fifth edition. In it Linnaeus divided the plant Kingdom into 24 classes. One, Cryptogamia, included all the plants with concealed reproductive parts (algae, fungi, mosses and liverworts and ferns).

(1751) was a summary of Linnaeus's thinking on plant classification and nomenclature, and an elaboration of the work he had previously published in (1736) and (1737). Other publications forming part of his plan to reform the foundations of botany include his and : all were printed in Holland (as were (1737) and (1735)), the Philosophia being simultaneously released in Stockholm.

Collections

At the end of his lifetime the Linnean collection in Uppsala was considered one of the finest collections of natural history objects in Sweden. Next to his own collection he had also built up a museum for the university of Uppsala, which was supplied by material donated by Carl Gyllenborg (in 1744-1745), crown-prince Adolf Fredrik (in 1745), Erik Petreus (in 1746), Claes Grill (in 1746), Magnus Lagerström (in 1748 and 1750) and Jonas Alströmer (in 1749). The relation between the museum and the private collection was not formalised and the steady flow of material from Linnean pupils were incorporated to the private collection rather than to the museum. Linnaeus felt his work was reflecting the harmony of nature and he said in 1754 "the earth is then nothing else but a museum of the all-wise creator's masterpieces, divided into three chambers". He had turned his own estate into a microcosm of that 'world museum'.

In April 1766 parts of the town were destroyed by a fire and the Linnean private collection was subsequently moved to a barn outside the town, and shortly afterwards to a single-room stone building close to his country house at Hammarby near Uppsala. This resulted in a physical separation between the two collections; the museum collection remained in the botanical garden of the university. Some material which needed special care (alcohol specimens) or ample storage space was moved from the private collection to the museum.

In Hammarby the Linnean private collections suffered seriously from damp and the depredations by mice and insects. Carl von Linné's son (Carl Linnaeus) inherited the collections in 1778 and retained them until his own death in 1783. Shortly after Carl von Linné's death his son confirmed that mice had caused "horrible damage" to the plants and that also moths and mould had caused considerable damage. He tried to rescue them from the neglect they had suffered during his father's later years, and also added further specimens. This last activity however reduced rather than augmented the scientific value of the original material.

In 1784 the young medical student James Edward Smith purchased the entire specimen collection, library, manuscripts, and correspondence of Carl Linnaeus from his widow and daughter and transferred the collections to London. Not all material in Linné's private collection was transported to England. Thirty-three fish specimens preserved in alcohol were not sent and were later lost.

In London Smith tended to neglect the zoological parts of the collection; he added some specimens and also gave some specimens away. Over the following centuries the Linnean collection in London suffered enormously at the hands of scientists who studied the collection, and in the process disturbed the original arrangement and labels, added specimens that did not belong to the original series and withdrew precious original type material.

Much material which had been intensively studied by Linné in his scientific career belonged to the collection of Queen Lovisa Ulrika (1720-1782) (in the Linnean publications referred to as "Museum Ludovicae Ulricae" or "M. L. U."). This collection was donated by her grandson King Gustav IV Adolf (1778-1837) to the museum in Uppsala in 1804. Another important collection in this respect was that of her husband King Adolf Fredrik (1710-1771) (in the Linnean sources known as "Museum Adolphi Friderici" or "Mus. Ad. Fr."), the wet parts (alcohol collection) of which were later donated to the Royal Swedish Academy of Sciences, and is today housed in the Swedish Museum of Natural History at Stockholm. The dry material was transferred to Uppsala.

System of taxonomy

The establishment of universally accepted conventions for the naming of organisms was Linnaeus's main contribution to taxonomy-his work marks the starting point of consistent use of binomial nomenclature. During the 18th century expansion of natural history knowledge, Linnaeus also developed what became known as the Linnaean taxonomy; the system of scientific classification now widely used in the biological sciences. A previous zoologist Rumphius (1627-1702) had more or less approximated the Linnaean system and his material contributed to the later development of the binomial scientific classification by Linnaeus.

The Linnaean system classified nature within a nested hierarchy, starting with three kingdoms. Kingdoms were divided into classes and they, in turn, into orders, and thence into genera ( singular: genus), which were divided into species ( singular: species). Below the rank of species he sometimes recognised taxa of a lower (unnamed) rank; these have since acquired standardised names such as variety in botany and subspecies in zoology. Modern taxonomy includes a rank of family between order and genus and a rank of phylum between kingdom and class that were not present in Linnaeus's original system.

Linnaeus's groupings were based upon shared physical characteristics, and not simply upon differences. Of his higher groupings, only those for animals are still in use, and the groupings themselves have been significantly changed since their conception, as have the principles behind them. Nevertheless, Linnaeus is credited with establishing the idea of a hierarchical structure of classification which is based upon observable characteristics and intended to reflect natural relationships. While the underlying details concerning what are considered to be scientifically valid "observable characteristics" have changed with expanding knowledge (for example, DNA sequencing, unavailable in Linnaeus's time, has proven to be a tool of considerable utility for classifying living organisms and establishing their evolutionary relationships), the fundamental principle remains sound.

Human taxonomy

Linnaeus's system of taxonomy was especially noted as the first to include humans () taxonomically grouped with apes (), under the header of Anthropomorpha. German biologist Ernst Haeckel speaking in 1907 noted this as the "most important sign of Linnaeus's genius".

Linnaeus classified humans among the primates beginning with the first edition of . During his time at Hartekamp, he had the opportunity to examine several monkeys and noted similarities between them and man. He pointed out both species basically have the same anatomy; except for speech, he found no other differences. Thus he placed man and monkeys under the same category, Anthropomorpha, meaning "manlike." This classification received criticism from other biologists such as Johan Gottschalk Wallerius, Jacob Theodor Klein and Johann Georg Gmelin on the ground that it is illogical to describe man as human-like. In a letter to Gmelin from 1747, Linnaeus replied:

It does not please [you] that I've placed Man among the Anthropomorpha, perhaps because of the term 'with human form', but man learns to know himself. Let's not quibble over words. It will be the same to me whatever name we apply. But I seek from you and from the whole world a generic difference between man and simian that [follows] from the principles of Natural History. I absolutely know of none. If only someone might tell me a single one! If I would have called man a simian or vice versa, I would have brought together all the theologians against me. Perhaps I ought to have by virtue of the law of the discipline.

The theological concerns were twofold: first, putting man at the same level as monkeys or apes would lower the spiritually higher position that man was assumed to have in the great chain of being, and second, because the Bible says man was created in the image of God ( theomorphism), if monkeys/apes and humans were not distinctly and separately designed, that would mean monkeys and apes were created in the image of God as well. This was something many could not accept. The conflict between world views that was caused by asserting man was a type of animal would simmer for a century until the much greater, and still ongoing, creation-evolution controversy began in earnest with the publication of On the Origin of Species by Charles Darwin in 1859.

After such criticism, Linnaeus felt he needed to explain himself more clearly. The 10th edition of introduced new terms, including Mammalia and Primates, the latter of which would replace Anthropomorpha as well as giving humans the full binomial Homo sapiens. The new classification received less criticism, but many natural historians still believed he had demoted humans from their former place of ruling over nature and not being a part of it. Linnaeus believed that man biologically belongs to the animal kingdom and had to be included in it. In his book , he said, "One should not vent one's wrath on animals, Theology decree that man has a soul and that the animals are mere 'aoutomata mechanica,' but I believe they would be better advised that animals have a soul and that the difference is of nobility."

Linnaeus added a second species to the genus Homo in based on a figure and description by Jacobus Bontius from a 1658 publication: Homo troglodytes ("caveman") and published a third in 1771: Homo lar. Swedish historian Gunnar Broberg states that the new human species Linnaeus described were actually simians or native people clad in skins to frighten colonial settlers, whose appearance had been exaggerated in accounts to Linnaeus.

In early editions of , many well-known legendary creatures were included such as the phoenix, dragon, manticore, and satyrus, which Linnaeus collected into the catch-all category . Broberg thought Linnaeus was trying to offer a natural explanation and demystify the world of superstition. Linnaeus tried to debunk some of these creatures, as he had with the hydra; regarding the purported remains of dragons, Linnaeus wrote that they were either derived from lizards or rays. For Homo troglodytes he asked the Swedish East India Company to search for one, but they did not find any signs of its existence. Homo lar has since been reclassified as Hylobates lar, the lar gibbon.

In the first edition of , Linnaeus subdivided the human species into four varieties based on continent and[dubious ] skin colour: "Europæus albesc[ens]" (whitish European), "Americanus rubesc[ens]" (reddish American), "Asiaticus fuscus" (tawny Asian) and "Africanus nigr[iculus]" (blackish African). In the tenth edition of Systema Naturae he further detailed phenotypical characteristics for each variety, based on the concept of the four temperaments from classical antiquity,[dubious ] and changed the description of Asians' skin tone to "luridus" (yellow). Additionally, Linnaeus created a wastebasket taxon "monstrosus" for "wild and monstrous humans, unknown groups, and more or less abnormal people".

Influences and economic beliefs

Commemoration

Anniversaries of Linnaeus's birth, especially in centennial years, have been marked by major celebrations. Linnaeus has appeared on numerous Swedish postage stamps and banknotes. There are numerous statues of Linnaeus in countries around the world. The Linnean Society of London has awarded the Linnean Medal for excellence in botany or zoology since 1888. Following approval by the Riksdag of Sweden, Växjö University and Kalmar College merged on 1 January 2010 to become Linnaeus University. Other things named after Linnaeus include the twinflower genus , Linnaeosicyos (a monotypic genus in the family Cucurbitaceae), the crater Linné on the Earth's moon, a street in Cambridge, Massachusetts, and the cobalt sulfide mineral Linnaeite.

Andrew Dickson White wrote in A History of the Warfare of Science with Theology in Christendom (1896):

Linnaeus ... was the most eminent naturalist of his time, a wide observer, a close thinker; but the atmosphere in which he lived and moved and had his being was saturated with biblical theology, and this permeated all his thinking. ... Toward the end of his life he timidly advanced the hypothesis that all the species of one genus constituted at the creation one species; and from the last edition of his Systema Naturæ he quietly left out the strongly orthodox statement of the fixity of each species, which he had insisted upon in his earlier works. ... warnings came speedily both from the Catholic and Protestant sides.

The mathematical PageRank algorithm, applied to 24 multilingual Wikipedia editions in 2014, published in in 2015, placed Carl Linnaeus at the top historical figure, above Jesus, Aristotle, Napoleon, and Adolf Hitler (in that order).

In the 21st century, Linnæus's taxonomy of human "races" has been problematised and discussed. Some critics[who? ] claim that Linnæus was one of the forebears of the modern pseudoscientific notion of scientific racism, while others[who? ] hold the view that while his classification was stereotyped, it did not imply that certain human "races" were superior to others.[citation needed ]

Standard author abbreviation

Selected publications by Linnaeus

Linnaeus, Carl (1735). Systema naturae, sive regna tria naturae systematice proposita per classes, ordines, genera, & species. Leiden: Haak. pp. 1-12.

Linnaeus, Carl; Hendrik Engel; Maria Sara Johanna Engel-Ledeboer (1964) [1735]. Systema Naturae (facsimile of the 1st ed.). Nieuwkoop, Netherlands: B. de Graaf. OCLC 460298195.

Linnaeus, Carl (1735). Systema naturae, sive regna tria naturae systematice proposita per classes, ordines, genera, & species. Leiden: Haak. pp. 1-12.

Linnaeus, Carl 1846 Fauna svecica. Sistens Animalia Sveciae Regni: Quadrupedia, Aves, Amphibia, Pisces, Insecta, Vermes, distributae per classes & ordines, genera & species. C. Wishoff & G.J. Wishoff, Lugdnuni Batavorum.

Linnaeus, Carl (1755) [1751]. Philosophia botanica: in qua explicantur fundamenta botanica cum definitionibus partium, exemplis terminorum, observationibus rariorum, adiectis figuris aeneis. originally published simultaneously by R. Kiesewetter (Stockholm) and Z. Chatelain (Amsterdam). Vienna: Joannis Thomae Trattner.

Linnaeus, Carl (1753). Species Plantarum: exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas. Stockholm: Impensis Laurentii Salvii. see also Species Plantarum

Linnaeus, Carl (1758). Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Vol. 1 (10th ed.). Stockholm: Laurentius Salvius. pp. [1-4], 1-824.

Linné, Carl von (1774). Murray, Johann Andreas (ed.). Systema vegetabilium (13th edition of Systema Naturae) (2 vols.). Göttingen: Typis et impensis Jo. Christ. Dieterich.

Linné, Carl von (1785) [1774]. Systema vegetabilium (13th edition of Systema Naturae) [A System of Vegetables 2 vols. 1783-1785]. Lichfield: Lichfield Botanical Society.

Linné, Carl von (1771). Mantissa plantarum altera generum editionis VI et specierum editionis II. Stockholm: Laurentius Salvius. pp. [1-7], 144-588. Archived from the original on 30 September 2011.

Linnaeus, Carl (1792). Giseke, Paul Dietrich (ed.). Praelectiones in ordines naturales plantarum. Hamburg: Benj. Gottl. Hoffmanni.

References

Bontius, J. (1658). "Historiae naturalis & medicae Indiae Orientalis libri sex". In Gulielmo Piso (ed.). De Indiæ Utriusque re naturali et medica libri quatuordecim. Quorum contenta pagina sequens exhibet. Amsterdam: Elzevier. pp. 1-226.

Broberg, G. (1975). Homo sapiens L. studien: Carl von Linné naturuppfattning och människolära. Uppsala: Almquist and Wiksell.

Broberg, Gunnar (2008). "The Dragonslayer". Tijdschrift voor Skandinavistiek. 29 (1-2): 29-43. Archived from the original on 12 January 2013.

Davis, P.H.; Heywood, V H. (1973). Principles of Angiosperm Taxonomy. Huntington, New York: Robert E. Krieger Publishing Company.

Fara, Patricia (2003). Sex, Botany and Empire: The Story of Carl Linnaeus and Joseph Banks. Cambridge: Icon Books. ISBN 978-1-84046-444-3.

Gribbin, Mary; Gribbin, John (2008). . Oxford: Oxford University Press. ISBN 978-0-19-956182-7.

Koerner, Lisbet (1999). Linnaeus: Nature and Nation. Harvard: Harvard University Press. ISBN 978-0-674-09745-2.

Östholm, Hanna (2007). Mary J. Morris and Leonie Berwick (ed.). "The Linnaean Legacy: Three Centuries after his Birth" (PDF). The Linnean. Special Issue No. 8: 35-44. Archived from the original (PDF) on 17 July 2011.

Quammen, David (June 2007). "The Name Giver". National Geographic.

Simpson, George Gaylord (1961). Principles of Animal Taxonomy. New York and London: Columbia University Press. ISBN 9780231024273.

Slotkin, J.S. (1965). "The Eighteenth Century". Readings in early Anthropology. Methuen Publishing. pp. 175-243.

Stöver, Dietrich Johann Heinrich (1794). Joseph Trapp (ed.). The life of Sir Charles Linnæus. London: Library of Congress. OCLC 5660395.

Veitch, H.J. (1897). "Nepenthes". Journal of the Royal Horticultural Society. 21 (2): 226-262.

Further reading

External links

Biographies

Resources

Other

Linnaeus was depicted by Jay Hosler in a parody of Peanuts titled "Good ol' Charlie Darwin".

The 15 March 2007 issue of featured a picture of Linnaeus on the cover with the heading "Linnaeus's Legacy" and devoted a substantial portion to items related to Linnaeus and Linnaean taxonomy.

A tattoo of Linnaeus's definition of the order Primates mentioned by Carl Zimmer

Ginkgo biloba tree at the University of Harderwijk, said to have been planted by Linnaeus in 1735

SL Magazine, Spring 2018 features an article by Nicholas Sparks, librarian, Collection Strategy and Development titled Origins of Taxonomy, describing a generous donation from the Linnean Society of NSW to supplement the State Library of New South Wales's collections on Carl Linnaeus of documents, photographs, prints and drawings as well as a fine portrait of Linnaeus painted about 1800.

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( Carl Linnaeus (;[1] [2] 23 May 1707 - 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné [3] ( Swedish pronunciation: [ˈkɑːɭ fɔn lɪˈneː] listen )), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the modern system of naming organisms. He is known as the "father of modern taxonomy".[4] Many of his writings were in Latin; his name is rendered in Latin as Carolus Linnæus and, after his 1761 ennoblement, as Carolus a Linné .

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The violet flower was a favorite in ancient Greece and became the symbol of Athens. Scent suggested sex, so the violet was an emblematic flower of Aphrodite and also of her son Priapus, the deity of gardens and generation.

Iamus was a son of Apollo and the nymph Evadne. He was abandoned by his mother at birth. She left him lying in the Arkadian wilds on a bed of violets where he was fed honey by serpents. Eventually, he was discovered by passing shepherds who named him Iamus after the violet (ion) bed.

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An optical spectrometer ( spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization state. The independent variable is usually the wavelength of the light or a unit directly proportional to the photon energy, such as reciprocal centimeters or electron volts, which has a reciprocal relationship to wavelength.

A spectrometer is used in spectroscopy for producing spectral lines and measuring their wavelengths and intensities. Spectrometers may operate over a wide range of non-optical wavelengths, from gamma rays and X-rays into the far infrared. If the instrument is designed to measure the spectrum on an absolute scale rather than a relative one, then it is typically called a spectrophotometer. The majority of spectrophotometers are used in spectral regions near the visible spectrum.

In general, any particular instrument will operate over a small portion of this total range because of the different techniques used to measure different portions of the spectrum. Below optical frequencies (that is, at microwave and radio frequencies), the spectrum analyzer is a closely related electronic device.

Spectrometers are used in many fields. For example, they are used in astronomy to analyze the radiation from objects and deduce their chemical composition. The spectrometer uses a prism or a grating to spread the light into a spectrum. This allows astronomers to detect many of the chemical elements by their characteristic spectral lines. These lines are named for the elements which cause them, such as the hydrogen alpha, beta, and gamma lines. A glowing object will show bright spectral lines. Dark lines are made by absorption, for example by light passing through a gas cloud, and these absorption lines can also identify chemical compounds. Much of our knowledge of the chemical makeup of the universe comes from spectra.

Spectroscopes are often used in astronomy and some branches of chemistry. Early spectroscopes were simply prisms with graduations marking wavelengths of light. Modern spectroscopes generally use a diffraction grating, a movable slit, and some kind of photodetector, all automated and controlled by a computer. Recent advances have seen increasing reliance of computational algorithms in a range of miniaturised spectrometers without diffraction gratings, for example, through the use of quantum dot-based filter arrays on to a CCD chip or a series of photodetectors realised on a single nanostructure.

Joseph von Fraunhofer developed the first modern spectroscope by combining a prism, diffraction slit and telescope in a manner that increased the spectral resolution and was reproducible in other laboratories. Fraunhofer also went on to invent the first diffraction spectroscope. Gustav Robert Kirchhoff and Robert Bunsen discovered the application of spectroscopes to chemical analysis and used this approach to discover caesium and rubidium. Kirchhoff and Bunsen's analysis also enabled a chemical explanation of stellar spectra, including Fraunhofer lines.

When a material is heated to incandescence it emits light that is characteristic of the atomic makeup of the material. Particular light frequencies give rise to sharply defined bands on the scale which can be thought of as fingerprints. For example, the element sodium has a very characteristic double yellow band known as the Sodium D-lines at 588.9950 and 589.5924 nanometers, the color of which will be familiar to anyone who has seen a low pressure sodium vapor lamp.

In the original spectroscope design in the early 19th century, light entered a slit and a collimating lens transformed the light into a thin beam of parallel rays. The light then passed through a prism (in hand-held spectroscopes, usually an Amici prism) that refracted the beam into a spectrum because different wavelengths were refracted different amounts due to dispersion. This image was then viewed through a tube with a scale that was transposed upon the spectral image, enabling its direct measurement.

With the development of photographic film, the more accurate spectrograph was created. It was based on the same principle as the spectroscope, but it had a camera in place of the viewing tube. In recent years, the electronic circuits built around the photomultiplier tube have replaced the camera, allowing real-time spectrographic analysis with far greater accuracy. Arrays of photosensors are also used in place of film in spectrographic systems. Such spectral analysis, or spectroscopy, has become an important scientific tool for analyzing the composition of unknown material and for studying astronomical phenomena and testing astronomical theories.

In modern spectrographs in the UV, visible, and near-IR spectral ranges, the spectrum is generally given in the form of photon number per unit wavelength (nm or μm), wavenumber (μm −1, cm −1), frequency (THz), or energy (eV), with the units indicated by the abscissa. In the mid- to far-IR, spectra are typically expressed in units of Watts per unit wavelength (μm) or wavenumber (cm −1). In many cases, the spectrum is displayed with the units left implied (such as "digital counts" per spectral channel).

In Gemology

Gemologists frequently use spectroscopes to determine the absorption spectra of gemstones, thereby allowing them to make inferences about what kind of gem they are examining. A gemologist may compare the absoprtion spectrum they observe with a catalogue of spectra for various gems to help narrow down the exact identity of the gem.

A spectrograph is an instrument that separates light by its wavelengths and records this data. A spectrograph typically has a multi-channel detector system or camera that detects and records the spectrum of light.

The term was first used in 1876 by Dr. Henry Draper when he invented the earliest version of this device, and which he used to take several photographs of the spectrum of Vega. This earliest version of the spectrograph was cumbersome to use and difficult to manage.

There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves. The first spectrographs used photographic paper as the detector. The plant pigment phytochrome was discovered using a spectrograph that used living plants as the detector. More recent spectrographs use electronic detectors, such as CCDs which can be used for both visible and UV light. The exact choice of detector depends on the wavelengths of light to be recorded.

A spectrograph is sometimes called polychromator, as an analogy to monochromator.

Stellar and solar spectrograph

The star spectral classification and discovery of the main sequence, Hubble's law and the Hubble sequence were all made with spectrographs that used photographic paper. The forthcoming James Webb Space Telescope will contain both a near-infrared spectrograph ( NIRSpec) and a mid-infrared spectrograph ( MIRI).

Echelle spectrograph

An Echelle spectrograph uses two diffraction gratings, rotated 90 degrees with respect to each other and placed close to one another. Therefore, an entrance point and not a slit is used and a 2d CCD-chip records the spectrum. Usually one would guess to retrieve a spectrum on the diagonal, but when both gratings have a wide spacing and one is blazed so that only the first order is visible and the other is blazed that a lot of higher orders are visible, one gets a very fine spectrum nicely folded onto a small common CCD-chip. The small chip also means that the collimating optics need not to be optimized for coma or astigmatism, but the spherical aberration can be set to zero.

Optical spectrometer at Curlie

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An optical spectrometer ( spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization state.

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Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spectrophotometers, that can measure the intensity of a light beam at different wavelengths. Although spectrophotometry is most commonly applied to ultraviolet, visible, and infrared radiation, modern spectrophotometers can interrogate wide swaths of the electromagnetic spectrum, including x-ray, ultraviolet, visible, infrared, and/or microwave wavelengths.

Spectrophotometry is a tool that hinges on the quantitative analysis of molecules depending on how much light is absorbed by colored compounds. Important features of spectrophotometers are spectral bandwidth (the range of colors it can transmit through the test sample), the percentage of sample-transmission, the logarithmic range of sample-absorption, and sometimes a percentage of reflectance measurement.

A spectrophotometer is commonly used for the measurement of transmittance or reflectance of solutions, transparent or opaque solids, such as polished glass, or gases. Although many biochemicals are colored, as in, they absorb visible light and therefore can be measured by colorimetric procedures, even colorless biochemicals can often be converted to colored compounds suitable for chromogenic color-forming reactions to yield compounds suitable for colorimetric analysis. However, they can also be designed to measure the diffusivity on any of the listed light ranges that usually cover around 200-2500 nm using different controls and calibrations. Within these ranges of light, calibrations are needed on the machine using standards that vary in type depending on the wavelength of the photometric determination.

An example of an experiment in which spectrophotometry is used in the determination of the equilibrium constant of a solution. A certain chemical reaction within a solution may occur in a forward and reverse direction, where reactants form products and products break down into reactants. At some point, this chemical reaction will reach a point of balance called an equilibrium point. In order to determine the respective concentrations of reactants and products at this point, the light transmittance of the solution can be tested using spectrophotometry. The amount of light that passes through the solution is indicative of the concentration of certain chemicals that do not allow light to pass through.

The absorption of light is due to the interaction of light with the electronic and vibrational modes of molecules. Each type of molecule has an individual set of energy levels associated with the makeup of its chemical bonds and nuclei and thus will absorb light of specific wavelengths, or energies, resulting in unique spectral properties. This is based upon its specific and distinct makeup.

The use of spectrophotometers spans various scientific fields, such as physics, materials science, chemistry, biochemistry, Chemical Engineering, and molecular biology. They are widely used in many industries including semiconductors, laser and optical manufacturing, printing and forensic examination, as well as in laboratories for the study of chemical substances. Spectrophotometry is often used in measurements of enzyme activities, determinations of protein concentrations, determinations of enzymatic kinetic constants, and measurements of ligand binding reactions. Ultimately, a spectrophotometer is able to determine, depending on the control or calibration, what substances are present in a target and exactly how much through calculations of observed wavelengths.

In astronomy, the term spectrophotometry refers to the measurement of the spectrum of a celestial object in which the flux scale of the spectrum is calibrated as a function of wavelength, usually by comparison with an observation of a spectrophotometric standard star, and corrected for the absorption of light by the Earth's atmosphere.

Invented by Arnold O. Beckman in 1940[disputed ], the spectrophotometer was created with the aid of his colleagues at his company National Technical Laboratories founded in 1935 which would become Beckman Instrument Company and ultimately Beckman Coulter. This would come as a solution to the previously created spectrophotometers which were unable to absorb the ultraviolet correctly. He would start with the invention of Model A where a glass prism was used to absorb the UV light. It would be found that this did not give satisfactory results, therefore in Model B, there was a shift from a glass to a quartz prism which allowed for better absorbance results. From there, Model C was born with an adjustment to the wavelength resolution which ended up having three units of it produced. The last and most popular model became Model D which is better recognized now as the DU spectrophotometer which contained the instrument case, hydrogen lamp with ultraviolet continuum and a better monochromator. It was produced from 1941 to 1976 where the price for it in 1941 was US$723 (far-UV accessories were an option at additional cost). In the words of Nobel chemistry laureate Bruce Merrifield, it was "probably the most important instrument ever developed towards the advancement of bioscience."

Once it became discontinued in 1976, Hewlett-Packard created the first commercially available diode-array spectrophotometer in 1979 known as the HP 8450A. Diode-array spectrophotometers differed from the original spectrophotometer created by Beckman because it was the first single-beam microprocessor-controlled spectrophotometer that scanned multiple wavelengths at a time in seconds. It irradiates the sample with polychromatic light which the sample absorbs depending on its properties. Then it is transmitted back by grating the photodiode array which detects the wavelength region of the spectrum. Since then, the creation and implementation of spectrophotometry devices has increased immensely and has become one of the most innovative instruments of our time.

There are two major classes of devices: single-beam and double-beam. A double-beam spectrophotometer compares the light intensity between two light paths, one path containing a reference sample and the other the test sample. A single-beam spectrophotometer measures the relative light intensity of the beam before and after a test sample is inserted. Although comparison measurements from double-beam instruments are easier and more stable, single-beam instruments can have a larger dynamic range and are optically simpler and more compact. Additionally, some specialized instruments, such as spectrophotometers built onto microscopes or telescopes, are single-beam instruments due to practicality.

Historically, spectrophotometers use a monochromator containing a diffraction grating to produce the analytical spectrum. The grating can either be movable or fixed. If a single detector, such as a photomultiplier tube or photodiode is used, the grating can be scanned stepwise (scanning spectrophotometer) so that the detector can measure the light intensity at each wavelength (which will correspond to each "step"). Arrays of detectors (array spectrophotometer), such as charge coupled devices (CCD) or photodiode arrays (PDA) can also be used. In such systems, the grating is fixed and the intensity of each wavelength of light is measured by a different detector in the array. Additionally, most modern mid-infrared spectrophotometers use a Fourier transform technique to acquire the spectral information. This technique is called Fourier transform infrared spectroscopy.

When making transmission measurements, the spectrophotometer quantitatively compares the fraction of light that passes through a reference solution and a test solution, then electronically compares the intensities of the two signals and computes the percentage of transmission of the sample compared to the reference standard. For reflectance measurements, the spectrophotometer quantitatively compares the fraction of light that reflects from the reference and test samples. Light from the source lamp is passed through a monochromator, which diffracts the light into a "rainbow" of wavelengths through a rotating prism and outputs narrow bandwidths of this diffracted spectrum through a mechanical slit on the output side of the monochromator. These bandwidths are transmitted through the test sample. Then the photon flux density (watts per metre squared usually) of the transmitted or reflected light is measured with a photodiode, charge coupled device or other light sensor. The transmittance or reflectance value for each wavelength of the test sample is then compared with the transmission or reflectance values from the reference sample. Most instruments will apply a logarithmic function to the linear transmittance ratio to calculate the 'absorbency' of the sample, a value which is proportional to the 'concentration' of the chemical being measured.

In short, the sequence of events in a scanning spectrophotometer is as follows:

1. The light source is shone into a monochromator, diffracted into a rainbow, and split into two beams. It is then scanned through the sample and the reference solutions.

2. Fractions of the incident wavelengths are transmitted through, or reflected from, the sample and the reference.

3. The resultant light strikes the photodetector device, which compares the relative intensity of the two beams.

4. Electronic circuits convert the relative currents into linear transmission percentages and/or absorbance/concentration values.

In an array spectrophotometer, the sequence is as follows:

1. The light source is shone into the sample and focused into a slit

2. The transmitted light is refracted into a rainbow with the reflection grating

3. The resulting light strikes the photodetector device which compares the intensity of the beam

4. Electronic circuits convert the relative currents into linear transmission percentages and/or absorbance/concentration values

Many older spectrophotometers must be calibrated by a procedure known as "zeroing", to balance the null current output of the two beams at the detector. The transmission of a reference substance is set as a baseline (datum) value, so the transmission of all other substances are recorded relative to the initial "zeroed" substance. The spectrophotometer then converts the transmission ratio into 'absorbency', the concentration of specific components of the test sample relative to the initial substance.

Applications in biochemistry

Spectrophotometry is an important technique used in many biochemical experiments that involve DNA, RNA, and protein isolation, enzyme kinetics and biochemical analyses.[15] Since samples in these applications are not readily available in large quantities, they are especially suited to being analyzed in this non-destructive technique. In addition, precious sample can be saved by utilizing a micro-volume platform where as little as 1uL of sample is required for complete analyses.[16] A brief explanation of the procedure of spectrophotometry includes comparing the absorbency of a blank sample that does not contain a colored compound to a sample that contains a colored compound. This coloring can be accomplished by either a dye such as Coomasie Brilliant Blue G-250 dye measured at 595 nm or by an enzymatic reaction as seen between β-galactosidase and ONPG (turns sample yellow) measured at 420 nm.[3]: 21-119  The spectrophotometer is used to measure colored compounds in the visible region of light (between 350 nm and 800 nm),[3]: 65  thus it can be used to find more information about the substance being studied. In biochemical experiments, a chemical and/or physical property is chosen and the procedure that is used is specific to that property in order to derive more information about the sample, such as the quantity, purity, enzyme activity, etc. Spectrophotometry can be used for a number of techniques such as determining optimal wavelength absorbance of samples, determining optimal pH for absorbance of samples, determining concentrations of unknown samples, and determining the pKa of various samples.[3]: 21-119  Spectrophotometry is also a helpful process for protein purification[17] and can also be used as a method to create optical assays of a compound. Spectrophotometric data can also be used in conjunction with the Beer-Lambert Equation, , in order to determine various relationships between transmittance and concentration, and absorbance and concentration.[3]: 21-119  Because a spectrophotometer measures the wavelength of a compound through its color, a dye binding substance can be added so that it can undergo a color change and be measured.[18] It is possible to know the concentrations of a two component mixture using the absorption spectra of the standard solutions of each component. To do this, it is necessary to know the extinction coefficient of this mixture at two wave lengths and the extinction coefficients of solutions that contain the known weights of the two components.[19] In addition to the traditional Beer-Lamberts law model, cuvette based label free spectroscopy can be used, which add an optical filter in the pathways of the light, enabling the spectrophotometer to quantify concentration, size and refractive index of samples following the hands law.[20] Spectrophotometers have been developed and improved over decades and have been widely used among chemists. Additionally, Spectrophotometers are specialized to measure either UV or Visible light wavelength absorbance values.[3]: 21-119  It is considered to be a highly accurate instrument that is also very sensitive and therefore extremely precise, especially in determining color change.[21] This method is also convenient for use in laboratory experiments because it is an inexpensive and relatively simple process.

Most spectrophotometers are used in the UV and visible regions of the spectrum, and some of these instruments also operate into the near- infrared region as well. The concentration of a protein can be estimated by measuring the OD at 280 nm due to the presence of tryptophan, tyrosine and phenylalanine. This method is not very accurate since the composition of proteins varies greatly and proteins with none of these amino acids do not have maximum absorption at 280 nm. Nucleic acid contamination can also interfere. This method requires a spectrophotometer capable of measuring in the UV region with quartz cuvettes.

Ultraviolet-visible (UV-vis) spectroscopy involves energy levels that excite electronic transitions. Absorption of UV-vis light excites molecules that are in ground-states to their excited-states.

Visible region 400-700 nm spectrophotometry is used extensively in colorimetry science. It is a known fact that it operates best at the range of 0.2-0.8 O.D. Ink manufacturers, printing companies, textiles vendors, and many more, need the data provided through colorimetry. They take readings in the region of every 5-20 nanometers along the visible region, and produce a spectral reflectance curve or a data stream for alternative presentations. These curves can be used to test a new batch of colorant to check if it makes a match to specifications, e.g., ISO printing standards.

Traditional visible region spectrophotometers cannot detect if a colorant or the base material has fluorescence. This can make it difficult to manage color issues if for example one or more of the printing inks is fluorescent. Where a colorant contains fluorescence, a bi-spectral fluorescent spectrophotometer is used. There are two major setups for visual spectrum spectrophotometers, d/8 (spherical) and 0/45. The names are due to the geometry of the light source, observer and interior of the measurement chamber. Scientists use this instrument to measure the amount of compounds in a sample. If the compound is more concentrated more light will be absorbed by the sample; within small ranges, the Beer-Lambert law holds and the absorbance between samples vary with concentration linearly. In the case of printing measurements two alternative settings are commonly used- without/with uv filter to control better the effect of uv brighteners within the paper stock.

Samples are usually prepared in cuvettes; depending on the region of interest, they may be constructed of glass, plastic (visible spectrum region of interest), or quartz (Far UV spectrum region of interest). Some applications require small volume measurements which can be performed with micro-volume platforms.

Applications

Experimental application

As described in the applications section, spectrophotometry can be used in both qualitative and quantitative analysis of DNA, RNA, and proteins. Qualitative analysis can be used and spectrophotometers are used to record spectra of compounds by scanning broad wavelength regions to determine the absorbance properties (the intensity of the color) of the compound at each wavelength. One experiment that can demonstrate the various uses that visible spectrophotometry can have is the separation of β-galactosidase from a mixture of various proteins. Largely, spectrophotometry is best used to help quantify the amount of purification your sample has undergone relative to total protein concentration. By running an affinity chromatography, B-Galactosidase can be isolated and tested by reacting collected samples with ONPG and determining if the sample turns yellow. Following this testing the sample at 420 nm for specific interaction with ONPG and at 595 for a Bradford Assay the amount of purification can be assessed quantitatively. In addition to this spectrophotometry can be used in tandem with other techniques such as SDS-Page electrophoresis in order to purify and isolate various protein samples.

Spectrophotometers designed for the infrared region are quite different because of the technical requirements of measurement in that region. One major factor is the type of photosensors that are available for different spectral regions, but infrared measurement is also challenging because virtually everything emits IR light as thermal radiation, especially at wavelengths beyond about 5 μm.

Another complication is that quite a few materials such as glass and plastic absorb infrared light, making it incompatible as an optical medium. Ideal optical materials are salts, which do not absorb strongly. Samples for IR spectrophotometry may be smeared between two discs of potassium bromide or ground with potassium bromide and pressed into a pellet. Where aqueous solutions are to be measured, insoluble silver chloride is used to construct the cell.

Spectroradiometers, which operate almost like the visible region spectrophotometers, are designed to measure the spectral density of illuminants. Applications may include evaluation and categorization of lighting for sales by the manufacturer, or for the customers to confirm the lamp they decided to purchase is within their specifications. Components:

1. The light source shines onto or through the sample.

2. The sample transmits or reflects light.

3. The detector detects how much light was reflected from or transmitted through the sample.

4. The detector then converts how much light the sample transmitted or reflected into a number.

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Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spectrophotometers, that can measure the intensity of a light beam at different wavelengths.

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A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the spectral components are somehow mixed. In visible light a spectrometer can separate white light and measure individual narrow bands of color, called a spectrum. A mass spectrometer measures the spectrum of the masses of the atoms or molecules present in a gas. The first spectrometers were used to split light into an array of separate colors. Spectrometers were developed in early studies of physics, astronomy, and chemistry. The capability of spectroscopy to determine chemical composition drove its advancement and continues to be one of its primary uses. Spectrometers are used in astronomy to analyze the chemical composition of stars and planets, and spectrometers gather data on the origin of the universe.

Examples of spectrometers are devices that separate particles, atoms, and molecules by their mass, momentum, or energy. These types of spectrometers are used in chemical analysis and particle physics.

Optical spectrometers or optical emission spectrometer

Optical spectrometers (often simply called "spectrometers"), in particular, show the intensity of light as a function of wavelength or of frequency. The different wavelengths of light are separated by refraction in a prism or by diffraction by a diffraction grating. Ultraviolet-visible spectroscopy is an example.

These spectrometers utilize the phenomenon of optical dispersion. The light from a source can consist of a continuous spectrum, an emission spectrum (bright lines), or an absorption spectrum (dark lines). Because each element leaves its spectral signature in the pattern of lines observed, a spectral analysis can reveal the composition of the object being analyzed.

Optical emission spectrometers (often called "OES or spark discharge spectrometers"), is used to evaluate metals to determine the chemical composition with very high accuracy. A spark is applied through a high voltage on the surface which vaporizes particles into a plasma. The particles and ions then emit radiation that is measured by detectors (photomultiplier tubes) at different characteristic wavelengths.

Electron spectroscopy

Some forms of spectroscopy involve analysis of electron energy rather than photon energy. X-ray photoelectron spectroscopy is an example.

Mass spectrometer

A mass spectrometer is an analytical instrument that is used to identify the amount and type of chemicals present in a sample by measuring the mass-to-charge ratio and abundance of gas-phase ions.

The energy spectrum of particles of known mass can also be measured by determining the time of flight between two detectors (and hence, the velocity) in a time-of-flight spectrometer. Alternatively, if the velocity is known, masses can be determined in a time-of-flight mass spectrometer.

When a fast charged particle (charge q, mass m) enters a constant magnetic field B at right angles, it is deflected into a circular path of radius r, due to the Lorentz force. The momentum p of the particle is then given by

,

where m and v are mass and velocity of the particle. The focusing principle of the oldest and simplest magnetic spectrometer, the semicircular spectrometer, invented by J. K. Danisz, is shown on the left. A constant magnetic field is perpendicular to the page. Charged particles of momentum p that pass the slit are deflected into circular paths of radius r = p/qB. It turns out that they all hit the horizontal line at nearly the same place, the focus; here a particle counter should be placed. Varying B, this makes possible to measure the energy spectrum of alpha particles in an alpha particle spectrometer, of beta particles in a beta particle spectrometer, of particles (e.g., fast ions) in a particle spectrometer, or to measure the relative content of the various masses in a mass spectrometer.

Since Danysz' time, many types of magnetic spectrometers more complicated than the semicircular type have been devised.

Generally, the resolution of an instrument tells us how well two close-lying energies (or wavelengths, or frequencies, or masses) can be resolved. Generally, for an instrument with mechanical slits, higher resolution will mean lower intensity.

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A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the spectral components are somehow mixed.

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Ångström , ångström , angström , ångstrom , or angstrom in Wiktionary, the free dictionary.

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Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics ( condensed matter physics). The word "crystallography" is derived from the Greek words κρύσταλλος ( krystallos) "clear ice, rock-crystal", with its meaning extending to all solids with some degree of transparency, and γράφειν ( graphein) "to write". In July 2012, the United Nations recognised the importance of the science of crystallography by proclaiming that 2014 would be the International Year of Crystallography.

Before the development of X-ray diffraction crystallography (see below), the study of crystals was based on physical measurements of their geometry using a goniometer. This involved measuring the angles of crystal faces relative to each other and to theoretical reference axes (crystallographic axes), and establishing the symmetry of the crystal in question. The position in 3D space of each crystal face is plotted on a stereographic net such as a Wulff net or Lambert net. The pole to each face is plotted on the net. Each point is labelled with its Miller index. The final plot allows the symmetry of the crystal to be established.

Crystallographic methods now depend on analysis of the diffraction patterns of a sample targeted by a beam of some type. X-rays are most commonly used; other beams used include electrons or neutrons. Crystallographers often explicitly state the type of beam used, as in the terms X-ray crystallography, neutron diffraction and electron diffraction. These three types of radiation interact with the specimen in different ways.

Because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies.

With conventional imaging techniques such as optical microscopy, obtaining an image of a small object requires collecting light with a magnifying lens. The resolution of any optical system is limited by the diffraction-limit of light, which depends on its wavelength. Thus, the overall clarity of resulting crystallographic electron density maps is highly dependent upon the resolution of the diffraction data, which can be categorized as: low, medium, high and atomic. For example, visible light has a wavelength of about 4000 to 7000 ångström, which is three orders of magnitude longer than the length of typical atomic bonds and atoms themselves (about 1 to 2 Å). Therefore, a conventional optical microscope cannot resolve the spatial arrangement of atoms in a crystal. To do so, we would need radiation with much shorter wavelengths, such as X-ray or neutron beams.

Unfortunately, focusing X-rays with conventional optical lens can be a challenge. Scientists have had some success focusing X-rays with microscopic Fresnel zone plates made from gold, and by critical-angle reflection inside long tapered capillaries. Diffracted X-ray or neutron beams cannot be focused to produce images, so the sample structure must be reconstructed from the diffraction pattern.

Diffraction patterns arise from the constructive interference of incident radiation (x-rays, electrons, neutrons), scattered by the periodic, repeating features of the sample. Because of their highly ordered and repetitive atomic structure ( Bravais lattice), crystals diffract x-rays in a coherent manner, also referred to as Bragg's reflection.

Coordinates in square brackets such as [100] denote a direction vector (in real space).

Coordinates in angle brackets or chevrons such as <100> denote a family of directions which are related by symmetry operations. In the cubic crystal system for example, <100> would mean [100], [010], [001] or the negative of any of those directions.

Miller indices in parentheses such as (100) denote a plane of the crystal structure, and regular repetitions of that plane with a particular spacing. In the cubic system, the normal to the (hkl) plane is the direction [hkl], but in lower-symmetry cases, the normal to (hkl) is not parallel to [hkl].

Indices in curly brackets or braces such as {100} denote a family of planes and their normals. In cubic materials the symmetry makes them equivalent, just as the way angle brackets denote a family of directions. In non-cubic materials, <hkl> is not necessarily perpendicular to {hkl}.

Some materials that have been analyzed crystallographically, such as proteins, do not occur naturally as crystals. Typically, such molecules are placed in solution and allowed to slowly crystallize through vapor diffusion. A drop of solution containing the molecule, buffer, and precipitants is sealed in a container with a reservoir containing a hygroscopic solution. Water in the drop diffuses to the reservoir, slowly increasing the concentration and allowing a crystal to form. If the concentration were to rise more quickly, the molecule would simply precipitate out of solution, resulting in disorderly granules rather than an orderly and usable crystal.

Once a crystal is obtained, data can be collected using a beam of radiation. Although many universities that engage in crystallographic research have their own X-ray producing equipment, synchrotrons are often used as X-ray sources, because of the purer and more complete patterns such sources can generate. Synchrotron sources also have a much higher intensity of X-ray beams, so data collection takes a fraction of the time normally necessary at weaker sources. Complementary neutron crystallography techniques are used to identify the positions of hydrogen atoms, since X-rays only interact very weakly with light elements such as hydrogen.

Producing an image from a diffraction pattern requires sophisticated mathematics and often an iterative process of modelling and refinement. In this process, the mathematically predicted diffraction patterns of a hypothesized or "model" structure are compared to the actual pattern generated by the crystalline sample. Ideally, researchers make several initial guesses, which through refinement all converge on the same answer. Models are refined until their predicted patterns match to as great a degree as can be achieved without radical revision of the model. This is a painstaking process, made much easier today by computers.

The mathematical methods for the analysis of diffraction data only apply to patterns, which in turn result only when waves diffract from orderly arrays. Hence crystallography applies for the most part only to crystals, or to molecules which can be coaxed to crystallize for the sake of measurement. In spite of this, a certain amount of molecular information can be deduced from patterns that are generated by fibers and powders, which while not as perfect as a solid crystal, may exhibit a degree of order. This level of order can be sufficient to deduce the structure of simple molecules, or to determine the coarse features of more complicated molecules. For example, the double-helical structure of DNA was deduced from an X-ray diffraction pattern that had been generated by a fibrous sample.

Crystallography is used by materials scientists to characterize different materials. In single crystals, the effects of the crystalline arrangement of atoms is often easy to see macroscopically because the natural shapes of crystals reflect the atomic structure. In addition, physical properties are often controlled by crystalline defects. The understanding of crystal structures is an important prerequisite for understanding crystallographic defects. Most materials do not occur as a single crystal, but are poly-crystalline in nature (they exist as an aggregate of small crystals with different orientations). As such, powder diffraction techniques, which takes diffraction patterns of polycrystalline samples with a large number of crystals, plays an important role in structural determination.

Other physical properties are also linked to crystallography. For example, the minerals in clay form small, flat, platelike structures. Clay can be easily deformed because the platelike particles can slip along each other in the plane of the plates, yet remain strongly connected in the direction perpendicular to the plates. Such mechanisms can be studied by crystallographic texture measurements.

In another example, iron transforms from a body-centered cubic (bcc) structure called ferrite to a face-centered cubic (fcc) structure called austenite when it is heated. The fcc structure is a close-packed structure unlike the bcc structure; thus the volume of the iron decreases when this transformation occurs.

Crystallography is useful in phase identification. When manufacturing or using a material, it is generally desirable to know what compounds and what phases are present in the material, as their composition, structure and proportions will influence the material's properties. Each phase has a characteristic arrangement of atoms. X-ray or neutron diffraction can be used to identify which structures are present in the material, and thus which compounds are present. Crystallography covers the enumeration of the symmetry patterns which can be formed by atoms in a crystal and for this reason is related to group theory.

X-ray crystallography is the primary method for determining the molecular conformations of biological macromolecules, particularly protein and nucleic acids such as DNA and RNA. In fact, the double-helical structure of DNA was deduced from crystallographic data. The first crystal structure of a macromolecule was solved in 1958, a three-dimensional model of the myoglobin molecule obtained by X-ray analysis. The Protein Data Bank (PDB) is a freely accessible repository for the structures of proteins and other biological macromolecules. Computer programs such as RasMol, Pymol or VMD can be used to visualize biological molecular structures. Neutron crystallography is often used to help refine structures obtained by X-ray methods or to solve a specific bond; the methods are often viewed as complementary, as X-rays are sensitive to electron positions and scatter most strongly off heavy atoms, while neutrons are sensitive to nucleus positions and scatter strongly even off many light isotopes, including hydrogen and deuterium. Electron crystallography has been used to determine some protein structures, most notably membrane proteins and viral capsids.

A number of women were pioneers in X-ray crystallography at a time when they were excluded from most other branches of physical science.

Kathleen Lonsdale was a research student of William Henry Bragg, who with his son Lawrence founded the science of X-ray crystallography at the beginning of the 20th century. She is known for both her experimental and theoretical work. Bragg had 11 women research students out of a total of 18. Kathleen joined his crystallography research team at the Royal Institution in London in 1923, and after getting married and having children, went back to work with Bragg as a researcher. She confirmed the structure of the benzene ring, carried out studies of diamond, was one of the first two women to be elected to the Royal Society in 1945, and in 1949 was appointed the first female tenured professor of chemistry and head of the Department of crystallography at University College London. Kathleen always advocated greater participation of women in science and said in 1970: "Any country that wants to make full use of all its potential scientists and technologists could do so, but it must not expect to get the women quite so simply as it gets the men.... It is utopian, then, to suggest that any country that really wants married women to return to a scientific career, when her children no longer need her physical presence, should make special arrangements to encourage her to do so?". During this period, Kathleen began a collaboration with William T. Astbury on a set of 230 space group tables which was published in 1924 and became an essential tool for crystallographers.

In 1932 Dorothy Hodgkin joined the laboratory of the physicist John Desmond Bernal, who was a former student of Bragg, in Cambridge, UK. She and Bernal took the first X-ray photographs of crystalline proteins. Hodgkin also played a role in the foundation of the International Union of Crystallography. She was awarded the Nobel Prize in Chemistry in 1964 for her work using X-ray techniques to study the structures of penicillin, insulin and vitamin B12. Her work on penicillin began in 1942 during the war and on vitamin B12 in 1948. While her group slowly grew, their predominant focus was on the X-ray analysis of natural products. She is the only British woman ever to have won a Nobel Prize in a science subject.

Rosalind Franklin took the X-ray photograph of a DNA fibre that proved key to James Watson and Francis Crick's discovery of the double helix, for which they both won the Nobel Prize for Physiology or Medicine in 1962. Watson revealed in his autobiographic account of the discovery of the structure of DNA, The Double Helix, that he had used Rosalind's X-ray photograph without her permission. Franklin died of cancer in her 30s, before Watson received the Nobel Prize. Franklin also carried out important structural studies of carbon in coal and graphite, and of plant and animal viruses.

Isabella Karle of the United States Naval Research Laboratory developed an experimental approach to the mathematical theory of crystallography. Her work improved the speed and accuracy of chemical and biomedical analysis. Yet only her husband Jerome shared the 1985 Nobel Prize in Chemistry with Herbert Hauptman, "for outstanding achievements in the development of direct methods for the determination of crystal structures". Other prize-giving bodies have showered Isabella with awards in her own right.

Women have written many textbooks and research papers in the field of X-ray crystallography. For many years Lonsdale edited the International Tables for Crystallography, which provide information on crystal lattices, symmetry, and space groups, as well as mathematical, physical and chemical data on structures. Olga Kennard of the University of Cambridge, founded and ran the Cambridge Crystallographic Data Centre, an internationally recognized source of structural data on small molecules, from 1965 until 1997. Jenny Pickworth Glusker, a British scientist, co-authored Crystal Structure Analysis: A Primer, first published in 1971 and as of 2010 in its third edition. Eleanor Dodson, an Australian-born biologist, who began as Dorothy Hodgkin's technician, was the main instigator behind CCP4, the collaborative computing project that currently shares more than 250 software tools with protein crystallographers worldwide.

The International Tables for Crystallography is an eight-book series that outlines the standard notations for formatting, describing and testing crystals. The series contains books that covers analysis methods and the mathematical procedures for determining organic structure through x-ray crystallography, electron diffraction, and neutron diffraction. The International tables are focused on procedures, techniques and descriptions and do not list the physical properties of individual crystals themselves. Each book is about 1000 pages and the titles of the books are:

Vol A - Space Group Symmetry,

Vol A1 - Symmetry Relations Between Space Groups,

Vol B - Reciprocal Space,

Vol C - Mathematical, Physical, and Chemical Tables,

Vol D - Physical Properties of Crystals,

Vol E - Subperiodic Groups,

Vol F - Crystallography of Biological Macromolecules, and

Vol G - Definition and Exchange of Crystallographic Data.

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Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics ( condensed matter physics). The word "crystallography" is derived from the Greek words κρύσταλλος ( krystallos) "clear ice, rock-crystal", with its meaning extending to all solids with some degree of transparency, and γράφειν ( graphein) "to write".

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Anders Jonas Ångström, (born August 13, 1814, Lögdö, Sweden—died June 21, 1874, Uppsala), Swedish physicist, a founder of spectroscopy for whom the angstrom, a unit of length equal to 10−10 metre, was named.

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The Editors of Encyclopaedia Britannica Edit History

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Anders Jonas Ångström | Biography and Facts

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Anders Jonas Ångström, (born August 13, 1814, Lögdö, Sweden—died June 21, 1874, Uppsala), Swedish physicist, a founder of spectroscopy for whom the angstrom, a unit of length equal to 10−10 metre, was named. Ångstrom received a doctorate at Uppsala University in 1839, and he became an observer at U…