Robert Boyle published "The Sceptical Chymist" which distinguished between the fields of chemistry and alchemy. The work also features some of the earliest recored ideas of atoms, molecules, and chemical reactions.;
Henry Cavendish discoveres hydrogen. He discribes it as a colorless, odourless gas that burns and can form an explosive mixture with air.
Carl Wihelm Scheele and Joseph Pristly isolate oxygen.
Antoine Lavoisier made the first extensive list of elements. The list featured 33 different elements and differentiated between metals and non-metals
John Dalton proposes "Dalton's Law" which describes the relationship between the different components in a mixture of gases. This discovery helps future scientists isolate a mixture of gases for individual study.
Elements Represented as Letters
Jakob Berzelius developes a talbe of atomic weights for several elements. This was the first table the represented different elements with letters.
Elements are Grouped
Johann Dobereiner discovers that there are groups of three elements that have simialr properites.
Periodic Table Rearranged
John Newlands arranges the known elements in order of atomic weight and observes similarities between some elements.
Valence Introduced to the Periodic Talbe
Lothar Meyer develops a periodic table with 28 elements. The elements were organized according to valence.
Periodic Table with Blanks
Dmitri Mendeleev produces a peridic table based on atomic weights. This periodic table featured elements with similar properties being placed in groups under each other. This periodic table featured 66 known elements and had blank spaces for elements that he believed would be discovered in the future.
Radioactive Elements Discovered
Marie and Pierre Curie isolate radium and polonium.
Periodic Table Arranged by Atomic Number
Henry Moseley determines the atomic number of each known element and rearranges the periodic table based on atomic number.
James Chadwick discovers neutrons, which identifies isotopes. This demonstrated why there was a discrepency between atomic number and atomic weight.
First Synthesized Element
Edwin McMillan and Philip H. Abelson identify neptunium, the first synthesized element. This was discovered in the products of uranium fission.
Lanthanides and Actinides
Glenn Seaborg identifies lanthanides and actinides (atomic number greater than 92) which are placed below the periodic talbe.