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Democritus and Leucippus put forward the idea that everything is made up of tiny particles
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Lavoisier wrote down the first ever list of known elements, which at the time was 33. He organised them into metals and non-metals
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Dalton proposed the relationship between the components of a mixture of gases
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Berzelius introduced the idea of atomic weights, and created the one and two letter system to refer to elements
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Meyer developed an early periodic table, with 28 elements arranged by valence electrons
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He organised his periodic table in order of atomic weight, just like our current one. He had 66 elements, but left numerous spaces for elements he knew existed, but had not been discovered yet. Most of these elements have since been discovered.
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The Noble Gases were discovered by William Ramsey
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Rutherford discovers that the source of radioactivity is decaying atoms.
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Moseley worked out the atomic numbers as the number of protons in the atom
