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Helmenstine. A, (Nov,2020), "Periodic Table Definition in Chemistry, ThoughtCo.

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-Arragement of the chemical elements.
- Made it to see trends in the elements properties.

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- Prout noticed how there was many elements had atomic weights.
-Hydrogen was some sort of (primer matter).
-He build a table of relative molar masses that was based on the gas densities.

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Triad 1: Alkali metals; lithium, pottasium and sodium.
Triad 2: Alkaline earth metals; strodium, barium and calcium.
Triad 3: Halogens; Bromide, Lodine...
Triad 4: Sulphur, Tellurium and Selenium.
Triad 5: Iron, Cobalt and Nickel.

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Newlands’ octaves - Development of the periodic table - GCSE Chemistry (Single Science) Revision - BBC Bitesize

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- He arranged them in ascending order according to their atomic weights and discovered that the properties of every eighth element were the same.

- The law of octaves states that when the elements are arranged in ascending order of atomic mass, every eighth element has comparable properties.

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- Mendeleev "proposed to name the elements by 'periods' and 'groups', arranged with their atomic weights in ascending order, from left to right, within the same line down to the second and so on.

- In 1869 he published the first periodic table of the elements.

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Henry Moseley, justificó cuantitativamente el concepto de número atómico - Rincón educativo. (2022). Rincón Educativo. https://rinconeducativo.org

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- Henry Moseley, in 1912, demonstrates that the periodic table should be ordered by atomic number.

-His main contribution to science was the quantitative justification of the concept of atomic number in Moseley's Law.