1. Periodic Table Timeline

2. 440 BC
Democritus and Leucippus propose the idea of the atom, an indivisible particle that all matter is made of

3. 360 BC Plato coins the term “elements”

4. Aristotle proposes the four element theory: earth, air, fire and water
330 BC
Aristotle proposes the four element theory:
earth, air, fire and water

5. 1605
Sir Francis Bacon published “The Proficience and Advancement of Learning” which contained a description of what would be known as the Scientific Method

6. 1649
Hennig Brand becomes the first known discoverer of an element, phosphorus, from distilled human urine.

7. 1661 Robert Boyle distinguishes between chemistry and alchemy.

8. 1661
He also discusses some of the earliest ideas of atoms, molecules, and chemical reactions marking the beginning of the history of modern chemistry.

9. 1766 Henry Cavendish discovered hydrogen.

10.
Carl Wilhelm Scheele and Joseph Priestly independently isolated oxygen.

11. 1778
Antoine Lavoisier wrote the first extensive list of “elements” containing 33 elements and distinguished between metals and nonmetals.

12. 1778
(Some of his “elements” were later determined to be compounds and included both heat and light.)

13. John Dalton proposes the four principles of the modern atomic theory.
1803
John Dalton proposes the four principles of the modern atomic theory.

14. 1826
Jakob Berzelius developed a table of atomic weights and introduced letters to symbolize elements.

15. 1829
Johann Dobereiner developed groups of three elements with similar properties (called triads.)

16. 1864
John Newlands arranged the elements in order of atomic weights and observed similarities between some elements.

17. 1864 He developed the “Law of Octaves.”

18. 1864
Lothar Meyer develops an early version of the periodic table with 28 elements organized by valence.

19. 1869
Dmitri Mendeleev produced a table based on atomic weights but arranged “periodically” with elements of similar properties under each other.

20. 1869 His periodic table included the 66 known elements.

21. 1894 William Ramsay discovered the noble gases.

22. Marie and Pierre Curie isolated radium and polonium from pitchblende.
1898
Marie and Pierre Curie isolated radium and polonium from pitchblende.

23. 1913
Henry Moseley determined the atomic number of each of the elements and modified the “Periodic Law.”

24. 1940
Edwin McMillan and Philip H. Abelson identify neptunium, the lightest and first synthesized transuranium element, found in the products of uranium fission.

25. 1941
Glenn Seaborg synthesized and investigated 10 transuranium elements (the elements after uranium on the periodic table.)