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in 1669 (or later), Henig brand experiments with distilled human urine resulted in the production of a glowing white substance, which he called "cold fire" (kaltes Feuer).[4] He kept his discovery secret until 1680, when Irish chemist Robert Boyle rediscovered phosphorus and published his findings. The discovery of phosphorus helped to raise the question of what it meant for a substance to be an element.

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Dobereiner discovered that the relative atomic mass of the middle element in each triad was close to the average of the relative atomic masses of the other two elements. This gave other scientists a clue that relative atomic masses were important when arranging the elements.

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1789

Antoine Lavoisier, now known as the ‘father of modern chemistry,’ publishes a list of 33 elements or “simple substances,” as he calls them. Although his list includes things such as heat and light, it is a major departure from previous thinking about elements. For Lavoisier, an element represents the final stage of chemical decomposition. This view moves away from earlier metaphysical notions about the nature of elements and emphasizes what can be observed and measured.

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1805

John Dalton, a Manchester schoolteacher and a Quaker, revives the atomic theory of ancient Greek philosophers while making it quantitative. Dalton also provides a new list of elements but his includes the relative weights of atoms of each element compared with an atom of hydrogen, which is assigned a weight of one unit. This development provides a basis from which other chemists can begin to discern relationships between different elements and is an essential step in the development of the periodic table

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(In 1817, German chemist Johann Dobereginer classified elements having similar chemical properties into groups of three. These groups were called triads. He proposed a law known as
Dobereiner's law of triads.)arash
Picture-deeta

Nitayanta
Dobereiner found the properties of bromine a liquid seem halway between those of chlorine gas nd iodine solid.

Nisht
Such triads—including chlorine-bromine-iodine, calcium-strontium-barium, and sulfur-selenium-tellurium—were noted by the German chemist J.W. Döbereiner between 1817 and 1829. The triad was the earliest atomic-weight classification of the elements.

(Triad | Atomic Masses
Lithium | 6.94
Sodium | 22.99
Potassium | 39.1

Triad | Atomic Masses
Calcium | 40.1
Strontium | 87.6
Barium | 137.3

Triad | Atomic Masses
Chlorine | 35.4
Bromine | 79.9
Iodine | 126.9

Triad | Atomic Masses
Sulfur | 32.1
Selenium | 78.9
Tellurium | 127.6

Triad | Atomic Masses
Iron | 55.8
Cobalt | 58.9
Nickel | 58.7)deeta

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Explanation Video on Dobereiner's Triads | Science | Letstute

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Drawback of Dobereiner's triads:

He was not able to prepare triads of all the known elements.

All the known elements could not be arranged in the form of triads.

For very low mass or for very high mass elements, the law was not holding good.

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Rishi

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John Newlands was home-schooled by his father, and later studied at the Royal College of Chemistry. He was interested in social reform and during 1860 served as a volunteer with Giuseppe Garibaldi in his military campaign to unify Italy.

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Rishi

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Rishi

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In 1864 Newland published his concept of the periodicity of the chemical elements, which he had arranged in order of atomic weight.

He pointed out that every eighth element in this grouping shared a resemblance and suggested an analogy with the intervals of the musical scale.

The “law of octaves,” thus enunciated, was controversial at first but later, in 1865, was recognized as an important generalization in modern chemical theory.

Newlands collected his various papers in On the Discovery of the Periodic Law (1884).

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About Newland's Octaves...

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Rishi

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Drawbacks of Newland's law of octave:

Newland could arrange elements only up to calcium,

After calcium, every eighth element did not possess properties similar to that of the first.

Only 56 elements were known at the time of Newlands, but later several elements were discovered.

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1862-1867

Over a period of about five years, multiple scientists independently develop significant precursors to the periodic table. The first is French geologist Alexandre-Emile Béguyer De Chancourtois, who arranges the elements in a line in order of increasing atomic weight.

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1868

Julius Lothar Meyer, a German chemist, publishes a number of periodic tables that represent the discovery of a fully mature table system. However, although he successfully accommodates most of the more than 60 then-known elements, Lothar Meyer fails to predict any new or missing elements, with one exception. He made a tentative prediction for the existence of a single element that he believed would have an atomic weight of 44.55. This element would eventually be discovered in Sweden and named scandium. Its weight when first measured was 44.6

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Vaidehi, Dmitri Mendeleev

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https://www.youtube.com/watch?v=rz4Dd1I_fX0

Till 0.47 seconds only

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In 1869, just five years after John Newlands put forward his Law of Octaves, a Russian chemist called Dmitri Mendeleev published a periodic table. Mendeleev also arranged the elements known at the time in order of relative atomic mass, but he did some other things that made his table much more successful.

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Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.

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There are seven periods and eight groups in Mendeleev’s periodic table. Each group from I to VII are divided into two subgroups A and B.In order to classify elements, Mendeleev considered atomic masses as fundamental property. Based on atomic mass Mendeleev compared elements based on their atomic masses. He also studied their physical and chemical properties. While studying chemical properties he primarily considered the compounds formed by elements with oxygen and hydrogen as these elements forms compounds with most of the elements. After his study he started arranging the elements based on increasing atomic masses. With the physical and chemical properties he found that every eighth element has properties similar to first. So he placed every eighth element below the first. likewise he arranged all 63 elements in rows and columns. In Mendeleev’s Periodic table, the horizontal rows are called periods and vertical columns are called groups.

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https://www.electrochem.org/wp-content/uploads/2019/02/iStock-Periodic-Table_CROP-MIN-Dmitri-Mendeleev.jpg

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In 1863, there were 56 known elements with a new element being discovered at a rate of approximately one per year. Other scientists had previously identified periodicity of elements. John Newlands described a Law of Octaves, noting their periodicity according to relative atomic weight in 1864, publishing it in 1865. His proposal identified the potential for new elements such as germanium. The concept was criticized and his innovation was not recognized by the Society of Chemists until 1887. Another person to propose a periodic table was Lothar Meyer, who published a paper in 1864 describing 28 elements classified by their valence, but with no predictions of new elements.

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After becoming a teacher in 1867, Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868–1870). It was written as he was preparing a textbook for his course. This is when he made his most important discovery. As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table; he claimed to have envisioned the complete arrangement of the elements in a dream

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Dmitri Ivanovich Mendeleev   8 February 1834 – 2 February 1907 [OS 27 January 1834 – 20 January 1907]) was a Russian chemist and inventor. He is best remembered for formulating the Periodic Law and creating a farsighted 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 eight elements that were yet to be discovered.
In 1863, there were 56 known elements with a new element being discovered at a rate of approximately one per year. Other scientists had previously identified periodicity of elements. John Newlands described a Law of Octaves, noting their periodicity according to relative atomic weight in 1864, publishing it in 1865. His proposal identified the potential for new elements such as germanium. The concept was criticized and his innovation was not recognized by the Society of Chemists until 1887. Another person to propose a periodic table was Lothar Meyer, who published a paper in 1864 describing 28 elements classified by their valence, but with no predictions of new elements.

After becoming a teacher in 1867, Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868–1870). It was written as he was preparing a textbook for his course.[25] This is when he made his most important discovery.[25] As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table; he claimed to have envisioned the complete arrangement of the elements in a dream:[27][28][29][30][31]

I saw in a dream a table where all elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper, only in one place did a correction later seem necessary.

— Mendeleev, as quoted by Inostrantzev[32][33]

Unaware of the earlier work on periodic tables going on in the 1860s, he made the following table:

Cl 35.5 | K 39 | Ca 40
Br 80 | Rb 85 | Sr 88
I 127 | Cs 133 | Ba 137

By adding additional elements following this pattern, Mendeleev developed his extended version of the periodic table.[34][35] On 6 March 1869, he made a formal presentation to the Russian Chemical Society, titled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight (now called relative atomic mass) and valence.[36][37] This presentation stated that

1. The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties.

2. Elements which are similar regarding their chemical properties either have similar atomic weights (e.g., Pt, Ir, Os) or have their atomic weights increasing regularly (e.g., K, Rb, Cs).

3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.

4. The elements which are the most widely diffused have small atomic weights.

5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.

6. We must expect the discovery of many yet unknown elements – for example, two elements, analogous to aluminium and silicon, whose atomic weights would be between 65 and 75.

7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. (Tellurium's atomic weight is 127.6, and Mendeleev was incorrect in his assumption that atomic weight must increase with position within a period.)

8. Certain characteristic properties of elements can be foretold from their atomic weights.

Mendeleev published his periodic table of all known elements and predicted several new elements to complete the table in a Russian-language journal. Only a few months after, Meyer published a virtually identical table in a German-language journal.[38][39] Mendeleev has the distinction of accurately predicting the properties of what he called ekasilicon, ekaaluminium and ekaboron (germanium, gallium and scandium, respectively).[40][41]

Mendeleev also proposed changes in the properties of some known elements. Prior to his work, uranium was supposed to have valence 3 and atomic weight about 120. Mendeleev realized that these values did not fit in his periodic table, and doubled both to valence 6 and atomic weight 240 (close to the modern value of 238).[42]

For his predicted eight elements, he used the prefixes of eka, dvi, and tri (Sanskrit one, two, three) in their naming. Mendeleev questioned some of the currently accepted atomic weights (they could be measured only with a relatively low accuracy at that time), pointing out that they did not correspond to those suggested by his Periodic Law. He noted that tellurium has a higher atomic weight than iodine, but he placed them in the right order, incorrectly predicting that the accepted atomic weights at the time were at fault. He was puzzled about where to put the known lanthanides, and predicted the existence of another row to the table which were the actinides which were some of the heaviest in atomic weight. Some people dismissed Mendeleev for predicting that there would be more elements, but he was proven to be correct when Ga (gallium) and Ge (germanium) were found in 1875 and 1886 respectively, fitting perfectly into the two missing spaces.[43]

By using Sanskrit prefixes to name "missing" elements, Mendeleev may have recorded his debt to the Sanskrit grammarians of ancient India, who had created sophisticated theories of language based on their discovery of the two-dimensional patterns of speech sounds (arguably most strikingly exemplified by the Śivasūtras in Pāṇini's Sanskrit grammar). Mendeleev was a friend and colleague of the Sanskritist Otto von Böhtlingk, who was preparing the second edition of his book on Pāṇini[44] at about this time, and Mendeleev wished to honor Pāṇini with his nomenclature.[45][46][47]

The original draft made by Mendeleev would be found years later and published under the name Tentative System of Elements.[48]

Dmitri Mendeleev is often referred to as the Father of the Periodic Table. He called his table or matrix, "the Periodic System".[49]

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eka silicon

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Eka-aluminium and eka-silicon were the names given by Mendeleev for the then unknown elements gallium and germanium respectively. A recently discovered element was first named as eka-mercury.

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Eka-aluminium and eka-silicon were the names given by Mendeleev for the then unknown elements gallium and germanium respectively. A recently discovered element was first named as eka-mercury.

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Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.

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Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.

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Sahil [The Modern Periodic Table] [Grp-4'

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Sahil [The Modern Periodic Table] [Grp-4'

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In 1863 English chemist John Newlands divided the then discovered 56 elements into 11 groups, based on characteristics. In 1869 Russian chemist Dimitri Mendeleev started the development of the periodic table, arranging chemical elements by atomic mass.
Yet historians typically consider one event as marking the formal birth of the modern periodic table: on February 17, 1869, a Russian professor of chemistry, Dimitri Ivanovich Mendeleev, completed the first of his numerous periodic charts.

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Arranged according to increasing order of atomic number. No.of valence electrons of element show periodicity. The modern table is based on Mendeleev’s table

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The long form of periodic table consist of vertical columns called groups and horizontal rows called periods. Elements are arranged in the increasing order of atomic numbers. Elements in the modern periodic table are arranged in 7 periods and 18 groups.

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The long form of periodic table consist of vertical columns called groups and horizontal rows called periods. Elements are arranged in the increasing order of atomic numbers. Elements in the modern periodic table are arranged in 7 periods and 18 groups.

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The modern periodic table has following merits: I) The arrangement of the elements is based on a more fundamental property namely atomic number.II) In this periodic table the position of an element is related to the electronic configuration of its atom.

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The modern periodic table has following merits: I) The arrangement of the elements is based on a more fundamental property namely atomic number.II) In this periodic table the position of an element is related to the electronic configuration of its atom.

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Modern periodic table .when elements are arranged to increasing atomic number,those having an equal number of valence electrons occur at regular intervals.

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Sahil
vaidehi, Dmitri Mene
vaidehi, Dmitri Meneleev
Aarav Aarav Dmitri Ivano

Aarav
Aarav
Dmitri Ivanovich Mendeleev   8 February 1834 – 2 February 1907 [OS 27 January 1834 – 20 January 1907]) was a Russian chemist and inventor. He is best remembered for formulating the Periodic Law and creating a farsighted 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 eight elements that were yet to be discovered.
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Dmitri Mendeleev's Periodic
Dmitri Mendeleev's Periodic
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Ojas
Ojas
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Modern periodic table
Modern periodic table
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Sahil
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Vaidehi
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Groups in the Modern Periodic Table

Groups are the vertical columns in the modern or long form of the periodic table.

There are 18 groups in the periodic table.

These groups are numbered from 1 to 18.

Each group consists of elements having the same outer shell electronic configuration.

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The modern periodic table has following merits:I) The arrangement of the elements is based on a more fundamental property namely atomic number.II) In this periodic table the position of an element is related to the electronic configuration of its atom.
The modern periodic table has following merits:I) The arrangement of the elements is based on a more fundamental property namely atomic number.II) In this periodic table the position of an element is related to the electronic configuration of its atom.
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The long form of periodic table consist of vertical columns called groups and horizontal rows called periods. Elements are arranged in the increasing order of atomic numbers. Elements in the modern periodic table are arranged in 7 periods and 18 groups.
The long form of periodic table consist of vertical columns called groups and horizontal rows called periods. Elements are arranged in the increasing order of atomic numbers. Elements in the modern periodic table are arranged in 7 periods and 18 groups.
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Vaidehi, Dmitri Mend
Vaidehi, Dmitri Mendeleev
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Modern periodic table .when elements are arranged to increasing atomic number,those having an equal number of valence electrons occur at regular intervals.
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uranium
uranium
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Sahil vaideh

Sahil 
vaidehi, Dmitri Mene
vaidehi, Dmitri Meneleev
Aarav Aarav Dmitri Ivano

Aarav
Aarav
Dmitri Ivanovich Mendeleev   8 February 1834 – 2 February 1907 [OS 27 January 1834 – 20 January 1907]) was a Russian chemist and inventor. He is best remembered for formulating the Periodic Law and creating a farsighted 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 eight elements that were yet to be discovered.
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Dmitri Mendeleev's Periodic
Dmitri Mendeleev's Periodic 
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Modern periodic table
Modern periodic table 
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Sahil 
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Vaidehi
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Avanti
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Groups in the Modern Periodic Table
Groups are the vertical columns in the modern or long form of the periodic table.
There are 18 groups in the periodic table.
These groups are numbered from 1 to 18.
Each group consists of elements having the same outer shell electronic configuration.
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The modern periodic table in detail .

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After becoming a teacher in 1867, Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868–1870). It was written as he was preparing a textbook for his course. This is when he made his most important discovery. As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table; he claimed to have envisioned the complete arrangement of the elements in a dream

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In 1869, just five years after John Newlands put forward his Law of Octaves, a Russian chemist called Dmitri Mendeleev published a periodic table. Mendeleev also arranged the elements known at the time in order of relative atomic mass, but he did some other things that made his table much more successful.

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There are seven periods and eight groups in Mendeleev’s periodic table. Each group from I to VII are divided into two subgroups A and B.In order to classify elements, Mendeleev considered atomic masses as fundamental property. Based on atomic mass Mendeleev compared elements based on their atomic masses. He also studied their physical and chemical properties. While studying chemical properties he primarily considered the compounds formed by elements with oxygen and hydrogen as these elements forms compounds with most of the elements. After his study he started arranging the elements based on increasing atomic masses. With the physical and chemical properties he found that every eighth element has properties similar to first. So he placed every eighth element below the first. likewise he arranged all 63 elements in rows and columns. In Mendeleev’s Periodic table, the horizontal rows are called periods and vertical columns are called groups. 