1. Law of Conservation of Mass Who: Antoine Lavoisier Matter can't be created or destroyed When: 1785 Where: France

2. Law of Definite Proportions Who: Joseph Proust Compounds – Elements put together in fixed ratios C + O 2  CO 2 When: 1797 Where: France

3. Law of Multiple Proportions Who: John Dalton Two elements form more than one compound between themelementscompound The ratios of the masses of the second element which combine with a fixed mass of the first element will be small whole numbers. Where: EnglandWhen: 1803

4. Historical Perspectives Aristotle (350BC) in Greece Everything was fire, earth, air, or water No smallest part of matter

5. Democritus (400 BC) in Greece Atoms = smallest unit of elements Atomos = indivisible/uncuttable Historical Perspectives

6. Solid Sphere Model (1805) in England Developed an atomic theory Elements were made up of atoms Each element was composed of the same kind of atoms. Different elements were composed of different kinds of atoms. Compounds are composed of atoms in specific ratios. Atoms are not created or destroyed in a reaction. John Dalton

7. Problems with Dalton’s Atomic Theory? 1. Matter is composed of indivisible particles Atoms Can Be Divided, but only in a nuclear reaction 2. All atoms of a particular element are identical Does Not Account for Isotopes (atoms of the same element but a different mass due to a different number of neutrons)! 3. Different elements have different atoms YES! 4. Atoms combine in certain whole-number ratios YES! Called the Law of Definite Proportions 5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements. Yes, except for nuclear reactions that can change atoms of one element to a different element

8. What:  Atoms aren't smallest particle  Conducted experiment with a Cathode Ray Tube  Particles had a negative charge  Model = plum pudding When: 1897 Where: England J.J. Thomson

9. Cathode Ray Tube

10. What: Experiments to determine mass of electron Conducted the oil drop experiment Verified that electron is negatively charged No new model Where: AmericaWhen: 1910 Robert Millikan

11. Millikan Oil Drop Experiment Run Video

12. Ernest Rutherford Conducted Gold Foil experiment Proved nucleus is dense, positively charged core of atom When: 1911 Where: America Model = Mass Centered/ Stationary Planetary Model

13. Rutherford’s experiment. Run video

15. Results of foil experiment if Plum Pudding model had been correct.

16. What Actually Happened

17. Niels Bohr What: Pulsating Planetary Model Electrons can move between energy levels When: 1913 Where: Denmark

18. Bohr Model Energy Levels

19. Erwin Schrodinger Electron have dual wave-particle nature Foundation for quantum theory Model = Pulsating orbitals Math was used to predict path of the electron When: 1926 Where: Switzerland

20. James Chadwick Confirmed existence of neutron No new atomic model When: 1932 Where: England