2. Atomic Theorists The ‘Who’s Who’ of the atomic world

3. Democritus 450 BC One of the first atomic theories Matter is made up of small particles (atoms) and empty space

4. Lavoisier late 1700’s Law of Conversation of Mass No mass is gained or lost in a Chemical Reaction

5. Proust 1799 Law of Constant Composition A Compound always has the same elements in the same proportions by mass. Ex. Water 88% oxygen 12% hydrogen

6. John Dalton 1803 ( and the Atomic theory) Elements are made of indivisible atoms Atoms of the same element are identical but differ from other elements

7. Dalton Atoms are neither created nor destroyed in a chemical reaction – they are just re-arranged Compounds have the same relative numbers and kinds of atoms Ex. H 2 O and C 6 H 12 O 6

8. Benjamin Franklin 1706-1790 Identified two types of electrical charge which he called positive and negative.

9. Faraday 1839 Suggested that the structure of atoms was somehow related to electricity. Atoms contain particles with electrical charges

10. J. J. Thomson 1896 Using cathode ray tubes, he discovered the existence of a negatively charged particle in the atom Electron (e - )

11. Thomson Model is called the plum pudding model or chocolate chip cookie model Electrons are scattered throughout a positive sphere

12. Robert Millikan 1909 Using his oil drop experiment, he measured the electrical charge of the electron and its mass

13. Becquerel 1890’s Accidentally discovered radioactivity in 1892 by placing a rock on a piece of film The rock had Uranium in it.

14. Marie and Pierre Curie 1890’s Isolated 2 other radioactive elements Polonium and Radium

15. Ernest Rutherford 1911 Studied radioactivity further Found that atoms are more complex than previous studies had indicated. Found radioactive particles which he called alpha and beta particles.

16. Rutherford Using his gold foil experiment, he discovered that there is a dense middle portion of an atom Nucleus

17. Rutherford Rutherford’s model has the electrons circling a positively charged nucleus

18. Henry Moseley 1913 Identified the proton Atoms contain a unique number of positive charges

19. James Chadwick 1932 Discovered neutral particle in the atom Neutron (n°)

20. Niels Bohr Presented a model of the atom that was accepted for many years

21. Bohr The nucleus is the middle part of the atom, while the electrons ‘orbit’ the nucleus in fixed distances Bohr model called the solar system model

22. James Schrodinger Electrons are found in regions outside the nucleus They are not in specific orbits

23. Schrodinger Electron cloud model of the atom Model that is used by scientists today

24. Albert Einstein’s Lighter Side