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Lavoiser groups elements into metals and nonmetals based on their physical properties.
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He begins to group elements with simlar properties in to groups of three or triads.
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Dobereiner discovered the halogen triad made up of chlorine, bromine and iodine and a alkali metal triad of lithim, sodium and potassium
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In 1864, English chemist John Newlands noticed that, if the elements were arranged in order of atomic weight, there was a periodic similarity every 8 elements. He proposed his ‘law of octaves’ on this.
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In 1864, Lothar Meyer created a textbook that included an abbreviated version of a periodic table used to classify about half of the known elements.
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In 1868, Meyer constructed am extended table which he gabe to a colleague for evaluation.
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In 1869, Russian chemist Dmitri Mendeleev produced a periodic table based on atomic weights but arranged ‘periodically’. Elements with similar properties appeared under each other. Gaps were left for yet to be discovered elements.
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In 1914, Henry Moseley determined the atomic number of each of the known elements. He realised that, if the elements were arranged in order of increasing atomic number rather than atomic weight, they gave a better fit within the ‘periodic table’.
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Seaborg discovered the transuranium elements, atomic numbers 94-102