1. Atomic Theory The Who’s Who of Atoms

2. Democritus ~460 BCE. Defined atom as the “smallest bit of matter. 100 years later, Aristotle dismissed his idea as “worthless.”

3. John Dalton 1805 Said matter consisted of elementary lumpy particles First Atomic Theory 5 Parts to his model:

4. Dalton’s Atomic Model 1.All matter is made of tiny particles called atoms. 2.All atoms of one element are alike. 3.Atoms of one element are different from atoms of other elements. 4.Compounds are formed when atoms from different elements combine. 5.Chemical reactions involve re- arrangement of atoms, not changes in atoms themselves.

5. J.J. Thomson 1897 Discovered the electron with his Cathode Ray Tube Experiment Came up with the “Plum Pudding Model” of atom

6. Cathode Ray Tube Experiment

7. Plum Pudding Model “Real” Plum Pudding

8. Max Planck 1900 When you vibrate atoms enough (heat it until it glows), you only get energy in whole intervals: energy packets called “quanta.”

9. Ernest Rutherford 1911 Discovered the nucleus with his Gold Foil Experiment Nucleus: the small, dense, positively- charged center of the atom In 1919, he identified “protons”

11. Rutherford’s Atom

12. Robert A. Millikan 1916 Found charge and mass of electron with his Oil Drop Experiment

13. Oil Drop Experiment

14. Niels Bohr 1912 Developed planetary model of the atom Discovered that electrons move around the nucleus at set distances Called these “electron orbitals.”

15. Electron Orbitals

16. “Bohr Model” of the Atom

17. James Chadwick 1932 Discovered the neutron

18. So Then We Have This!

19. Let’s Memorize These Guys! It’s the least we can do to commemorate all their hard work! Quiz on Friday! 5 minute break? Then SUBATOMIC PARTICLES!