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440 BCE
The idea of the atom is put forward
Democritus and Leucippus put forward the idea that everything is made up of tiny particles -
The first list of known elements is written
Lavoisier wrote down the first ever list of known elements, which at the time was 33. He organised them into metals and non-metals -
Dalton's Law
Dalton proposed the relationship between the components of a mixture of gases -
Discovery of Atomic Weights and Symbols
Berzelius introduced the idea of atomic weights, and created the one and two letter system to refer to elements -
Early version of the periodic table is proposed
Meyer developed an early periodic table, with 28 elements arranged by valence electrons -
Mendeleev creates the periodic table
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. -
Discovery of the Noble Gases
The Noble Gases were discovered by William Ramsey -
Discovery of radioactivity
Rutherford discovers that the source of radioactivity is decaying atoms. -
Ruthorford put forward his model of the atom
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The atomic numbers are discovered
Moseley worked out the atomic numbers as the number of protons in the atom
