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100
Aristotle
330 BC
Aristotle discovered the 4 element theory: earth, air, fire and water. -
Antoine Lavoirier
1770-1789
Antoine Lavoisier, wrote a list of the first 33 elements. Lavoisier also seperated metals and non-metals. (Some of these elements were later found to be compounds and mixtures) -
Jons Jakob Berzelius
Berzelius developed a table that showed atomic wieght. He also introduced lettters to symbolize the elelments. -
Johann Dobereiner
Johann devceloped 'triads'. these are groups of 3 elements which had similar properties. Eg: Lithium, Sodium and Potassium form a triad. -
John Newlands
John arranged the known elements in order of their atomic weights and saw similarities between the first and nineth elements. He proposed the 'Law of Octaves'. -
Lother Meyer and Dmitri Mendeleev
Meyer created a Periodic Tablle of 56 elements based on their properties like molar volume when arranged in order of their atomic weights. Mendeleev created a table based on the elelmets atomic weights, but his were arranged with elelments with similar properties under each other. He left gaps in his periodic table for his predicted elements, he also predicted theier properties. -
William Ramsay
William discovered the Noble Gases. -
Henry Morsely
Henry determined the atomic number for each element. He modified the 'Periodic Law' so that the properties of the elements vary witrh their atomic numbers. -
Henry Morsely
He also predicted that there were 3 unknown elements between aluminium and gold. He also concluded that there were only 92 elements. -
Glenn Seaborg
Glenn discovered the rest of the elemnts after uranium.