Devised the system of using letters as symbols

1. Jons Berzelius Devised the system of using letters as symbols Calculated relative atomic masses 1828

2. Johann Wolfgang Döbereiner Devised ‘Triads’ of elements with similar chemical properties 1829

3. John Newlands Observed a ‘Law of Octaves’ in the chemical properties of elements 1864

4. Dmitri Mendeleev • Constructed a periodic table by arranging elements: • in order of increasing atomic mass • in vertical groups based on similar chemical properties He left gaps for undiscovered elements and reversed the order of some elements to make their chemical properties fit. 1869

5. Lothar Meyer Also constructed a periodic table- similar to that of Mendeleev 1870

6. William Ramsay Discovered and isolated the noble gases 1895

7. Marie Curie Suggested that radioactive atoms were unstable and that energy was emitted during disintegration Discovered radium and polonium 1903

8. Glenn Seaborg Synthesised many of the transuranium elements - the actinide block 1941

9. The End