1. The History of the Atom Part 2 – The discovery of subatomic particles When we last left the atom, it looked like this:

2. J.J. Thomson  Discovered the electron with cathode ray experiment  Plum pudding model

3. Chocolate Chip Cookie Chocolate chips are distributed throughout a cookie just as electrons are distributed throughout an atom Today’s Thomson Analogy

4. Cathode Ray that Thomson used showing how the electric beam is curved by the stream of electrons cathode tube anode Glass tube stand Alligator clip Thomson’s Experiment Video Thomson’s Experiment Video

5. Robert Millikan  An American  Discovered the charge/mass of the electron  Oil Drop Experiment

7. Oil Drop Experiment  Balanced the gravitational and electric forces on tiny charged droplets of oil suspended between two metal electrodes  By knowing the electric field, the charge on the oil droplet could be determined.  Repeating the experiment for many droplets, he found that the values measured were always multiples of the same number.

8. Electron  Smallest particle  Almost no mass  Negative charge  Abbreviated e -

9. Ernest Rutherford  Discovered that most of the atom is empty space using the gold foil experiment  Discovered the nucleus  Also given credit for coining the name proton

12. Gold Foil Experiment

14. Rutherford’s model   Mostly empty space   Center area is the Nucleus   Little Blue dots are electrons

15. Rutherford Analogy A peach A peach has a dense center known as the pit just like an atom has a dense but small center called the nucleus

16. James Chadwick Discovered the neutron in 1932

17. Protons and Neutrons Neutrons  Have no charge  Are responsible for isotopes  Roughly same mass as a proton  Found in the nucleus Protons are  Positive charged  Define an element  Has roughly same mass as a neutron  Found in the nucleus

18. Nucleus  Tiny dense region in the center of the atom  Over 99% of the mass of the atom found here.  Made of protons and neutrons AH Video Clip

19. Homework  Summarize the 9 scientists that we talked about the past 2 days on the Scientist Timeline Paper  You will not use all the blanks yet.