1. Dalton’s Atom Note: Atomic Weights are Incorrect

2. Discovery of the Electron JJ ThomsonSir William Crookes

3. Crookes Tube http://www.youtube.com/watch?v=7YHwMWcxeX8&feature=related

4. Juliusz Plucker’s Maltese Cross Experiment

5. Thomson’s Apparatus

6. Thomson’s Deflection Results Gas in TubeCathodeVelocity (m/sec)q/m (kg/C) AirAluminum2.7 x 10 7 1.4 x 10 -11 AirAluminum2.8 x 10 7 1.1 x 10 -11 AirAluminum2.2 x 10 7 1.2 x 10 -11 HydrogenAluminum2.4 x 10 7 1.6 x 10 -11 Carbon DioxideAluminum2.2 x 10 7 1.6 x 10 -11 AirPlatinum3.6 x 10 7 1.3 x 10 -11 AirPlatinum2.8 x 10 7 1.0 x 10 -11

7. Thomson’s Speculation … we have in the cathode rays matter in a new state, a state in which the subdivision of matter is carried very much further than in the ordinary gaseous state: a state in which all matter – that is, matter derived from different sources such as hydrogen, oxygen, etc. – is of one and the same kind: this matter being the substance from which the chemical elements are built up.

8. Charge of the Electron Robert Millikan (1868 - 1953)

9. Millikan’s Apparatus

10. http://www.youtube.com/watch?v=XMfYHag7Liw

11. Charge on Drop*Charge Diff.*Multiple of Chrg.**Integral Value 29.87 39.869.915.956 28.25-11.61-6.977 29.911.661.001 34.915.003.003 36.591.681.011 28.28-8.31-4.995 34.956.674.014 39.975.023.023 26.65-13.328.008 41.4715.099.069 30.00-11.74-7.057 33.553.352.012 * x 10 -19 C ** x (1.665 x 10 -19 C)

12. Ernest Rutherford (1871 - 1937) Worked with: Hans Geiger Ernest Marsden

13. Rutherford’s Experiment One day Geiger came to and said, “Don’t you think that young Marsden, whom I am training in radioactive methods, ought to begin a small research?” Now I had thought that too, so I said, “Why not let him see if any alpha particles can be scattered through a large angle?” I may tell you in confidence that I did not believe that there would be, since we knew the alpha particle was a very fast massive particle, with a great deal of energy, and you could show that if the scattering was due to the accumulated effect of a number of small scatterings the chance of an alpha particle being scattered backward was very small.

14. Gold Foil Experiment

15. Results of the Experiment Then I remember two or three days later Geiger coming to me in great excitement and saying, “We have been able to get some of the alpha particles coming backwards…” It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it cam back and hit you.