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-Britannica
-BBC
-sciencehistory.org

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https://www.britannica.com/biography/James-Chadwick

https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/

https://nationalmaglab.org/education/magnet-academy/history-of-electricity-magnetism/pioneers/william-crookes

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He proposed a model of the atom, a precursor of the Bohr model of the atom. He introduced the use of wave numbers into spectroscopy

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The word electron was not about so he was  initially naming it "electrine", and the word itself came in 1891.

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He was the physicist who introduced the term electron for the fundamental unit of electricity. This then laid the foundations for the eventual discovery of the particle by J. J. Thomson in 1897.He also estimated the number of molecules in a volume of gas under standard conditions. He published around 75 scientific papers during his lifetime. Stoney was professor of physics at Queens College Galway from 1857 to 1882.

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William Crooke was awarded a  Nobel Prize for Chemistry in 1907 for inventing Crookes Tube .

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JJ Thompson received  the Nobel Prize for Physics for his researches into the electrical conductivity of gases in 1906.

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Robert Milikan was awarded a Nobel Prize for Physics in 1923 for the measurement of the elementary electric charge and for his work on the photoelectric effect.

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Robert Milikan discovered the Elementary charge of an electron in 1910. He discovered that all the drops had charges that were simple multiples of a single integer, the electron's fundamental charge.

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Discovered : Proposed Model Of an Atom .

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Discovered : Proposed Model Of an Atom .

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Discovered : The Elementary Charge Of An Electron.

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Discovered : The Elementary Charge Of An Electron.

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Discovered :   The Electron    .                                      (then went on to propose a model for the structure of the atom)

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Discovered :   The Electron    .                                      (then went on to propose a model for the structure of the atom)

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-JJ Thompson discovered the electron in 1897, he used a plum pudding model to demonstrate the atom and the electron . He showed that cathode rays were composed of unknown negatively charged particles (electrons).

- He is also credited in finding the first  evidence for isotopes of a stable element (non radioactive ) . -1913

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The law led to the discovery of new elements like Hafnium (72), Technetium (43), Rhenium (75), etc. Using the concept of Atomic Number instead of Atomic Mass for arranging elements in the periodic table helped a lot in solving many variations .

THE LAW STATES : The square root of the frequency of the x-ray emitted by an atom is proportional to its atomic number.

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He was awarded The Nobel Prize in Chemistry 1908 "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances".

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Niels Bohr received the 1922 Nobel Prize in Physics for his work on atomic structures .

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James Chadwick was also presented with a Nobel prize in Physics in 1935 for his discovery of the neutron !

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Discovery of neutron (⚡3d animation) | Chadwick's experiment 🧪 | Chemistry,Class 11

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He Conducted an experiment he bombarded ( direct a stream of high-speed particles at substance ) the element Beryllium with alpha particles from the natural  natural radioactive decay of Polonium (Po).  This resulted in the radiation showing a high  penetration through a lead shield,  but at the time could not be explained via the particles that were known at the time .

Neutrons were discovered last due to the fact that scientists could not observe them as they were neutral and had no charge!

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-Elements are arranged in horizontal rows (periods) in order of increasing atomic mass.
-Elements of similar chemical properties are placed in vertical columns called groups
- The groups are alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, halogens, noble metals, and noble gases.
- The number of electrons in the outer shell of all the elements in a group is the same as the group number. So this means different groups are more reactive or less

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The genius of Mendeleev's periodic table - Lou Serico

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In Febuary 1896 Mendeleev put the elements in order of atomic pass creating the periodic table. While he was doing this he realised that the chemical properties of the elements and their compounds showed a periodic trend. Then he put the elements with similar chemical properties below eachother forming the groups for example the alkali metals. To make this work he left gaps for elements which had yet to be discovered and switched a few elements around to keep it consistent.

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John Newlands attempted this using only the 62 elements that were known at the time. He arranged them increasing in atomic mass and then saw the pattern where the first and eight were similar.

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The Bohr model shows that the electrons within the atom revolve around the nucleus .

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Newland's Octave Law | Periodic Classification | Class 12 Chemistry

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One Of Niels Bohr most important discovery was the proposal of a model of an atom  in which the electron was able to occupy only certain orbits around the nucleus. This atomic model was the first to use quantum theory, in that the electrons were limited to specific orbits around the nucleus.

In July 1913 He published a series of 3 papers introducing the model of the atom . This is now known as the Bohr Model

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The law provided a broad scope to order all known elements into a tabular form.
It was then rejected because it only worked up to the element calcium it was not true after that.

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This law states if the chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical properties occur after each interval of seven elements.
Every eighth element seemed to be similar, rather like every eighth note in music.
If we take the elements Li, Be, B, C, N, O, F and Na. Lithium is the first element and sodium the eight. Both sodium and lithium have similar chemical properties.

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Rutherford's Gold Foil Experiment - Quick and Simple!

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Ernest Rutherford discovered that the atom was mostly empty space , He drew this conclusion by conducting the Gold Foil Experiment . This is when a piece of gold foil was hit with alpha particles( a helium nucleus emitted by radioactive substances), which have a positive charge. Most alpha particles went straight through. This showed that the gold atoms were mostly empty space. Some particles had their paths bent at large angles. A few even bounced back. The only way this would happen was if the atom had a small, heavy region of positive charge inside it. This proved that that space was also dense .

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This was useful because it gave other scientist the idea that atomic mass is important when arranging elements.
Drawbacks of Dobereiner's law of triad were that, it was valid only for a few groups of elements known during that time. Also with more accurate measurements of atomic masses showed that the mid element of the triad did not really have the mean value of the sum of the other two elements of the triad.

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Dobereiner noticed a pattern with certain elements that had similar chemical and physical properties. He called these elements triads.The law of triads states that the arithmetic mean of the atomic masses of the first and third elements in a triad would be approximately equal to the atomic mass of the second element in that triad. He found that the atomic mass of the middle element out of three was approx equal to the mean of the first and third when arranged in increasing order of mass.

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The Dark Space that surrounds the cathode is now known as Crookes Dark space . The space is simply the dark space between the cathode glow and negative glow in a vacuum tube, this occurs when the pressure within the tube is low .

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Sir William Crooke researched electrical discharges through a rarefied gas (a gas with pressure much less than atmospheric pressure). This led him to observe the dark space that surround cathode rays. This experiment helped demonstrate that cathode rays travel in straight lines and that they also produce  phosphorescence .  Phosphorescence is luminescence that is caused by the absorption (take in) of hea t.

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Dalton's Atomic Theory | #aumsum #kids #science #education #children

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something extra: Daltons law of partial pressure

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something extra: Daltons law of partial pressure

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Dalton's law states that the total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert (give out) independently. He discovered this by combining unreactive gases of a known pressure. He then measured the pressure of the resulting mixture. He found that the total pressure of the mixture was always equal to the sum of all the pressures of the

individual gases before they were mixed.

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Discovery: electron for the fundamental unit of electricity

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Discovery: electron for the fundamental unit of electricity

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Moseley's law is an empirical law concerning the characteristic x-rays emitted by atoms. He carried out a systematic series of experiments which showed that the frequencies of the X-rays emitted from an elemental target under bombardment by cathode rays were characteristic of that element and could be used to identify the charge on its atomic nucleus.

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Discovered : Proved the existence of neutrons .

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Discovered : Proved the existence of neutrons .

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There are 5 points to it:
Atoms of a given element are identical in size, mass, and other properties.
Atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements can combine in simple whole number ratios to form chemical compounds.
However he was not fully correct after subatomic particles (protons,electrons and neutrons were discovered.

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It was created for miners safety in 1815.prevented the methane gas present in the depths of the mines from reacting with the flame and exploding

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Cathode Ray Tube | www.MyInterAcademy.com

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Millikan's oil drop experiment to determine charge of an electron - Chemistry

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-Potassium carbonate: used in production of glass
-Potassium hydroxide: detergent and liquid soap
-Potassium chloride: pharmaceuticals and saline drips

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Robert Milikan discovered the elementary charge of an electron .  By using The Oil Drop Experiment Robert Milikan sprayed tiny drops of oil into an enclosed chamber . He first measured how fast the oil droplets fell under the force of gravity . He then used x-rays to ionize (convert) air in the chamber .He found electrons attached themselves to the oil droplets .He then adjusted the voltage between the two plates above and below the chamber , this is so the drops would hang suspended in mid-air . Milikan was then able to calculate the mass and force of gravity on a singular drop, then calculated charge on the drop.
He determined the charge to be 1.5924×10−19C. Columbus  is for one ampere .

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the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them.

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He made this discovery by decomposing molten potassium hydroxide [KOH] with a voltaic battery. [A voltaic battery was the first electrical battery that could continuously provide an electric current to a circuit.] He ralised a tiny droplet of liquid metal formed when he applied electrolysis to a small amount of melted potash, and he named the element potassium then base on that.

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By experimenting with a Crookes/Cathode Ray/Tube. He found that by applying a magnetic field across the tube , there was no activity recorded. This meant that the charge had been bend away by the magnet . This proved that the negative charge and rays were inseparable .

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He made this discovery using a vaccum chamber to change the pressure in a gas. He did a series of experiments which he carefully observed.

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-Medical syringes: the plunge is pulled back creating space and reduces pressure. The liquid can be drawn up then  balancing the pressure to inside and outside.
- When on a plane and your ears pop because of the change in  pressure. This is because the pressure inside the body and outside don't balance.
A few other examples are deodrants and fizzy drinks cans.

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Chemistry: Boyle's Law (Gas Laws) with 2 examples | Homework Tutor

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Boyles law was formulated by Robert Boyle in 1662. It is in relation to the compression and expansion of at a constant temperature. It states that the pressure (p) of a given quantity of gas varies inversely with its volume (v) at constant temperature.