Dalton’s Atom

Note: Atomic Weights are Incorrect

Discovery of the Electron

JJ Thomson Sir William Crookes

Crookes Tube

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

Juliusz Plucker’s Maltese Cross Experiment

Thomson’s Apparatus

Thomson’s Deflection ResultsGas in Tube Cathode Velocity (m/sec) q/m (kg/C)

Air Aluminum 2.7 x 107 1.4 x 10-11

Air Aluminum 2.8 x 107 1.1 x 10-11

Air Aluminum 2.2 x 107 1.2 x 10-11

Hydrogen Aluminum 2.4 x 107 1.6 x 10-11

Carbon Dioxide Aluminum 2.2 x 107 1.6 x 10-11

Air Platinum 3.6 x 107 1.3 x 10-11

Air Platinum 2.8 x 107 1.0 x 10-11

Thomson’s Speculation

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

Charge of the Electron

Robert Millikan (1868 - 1953)

Millikan’s Apparatus

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

Charge on Drop* Charge Diff.* Multiple of Chrg.** Integral Value

29.87

39.86 9.91 5.95 6

28.25 -11.61 -6.97 7

29.91 1.66 1.00 1

34.91 5.00 3.00 3

36.59 1.68 1.01 1

28.28 -8.31 -4.99 5

34.95 6.67 4.01 4

39.97 5.02 3.02 3

26.65 -13.32 8.00 8

41.47 15.09 9.06 9

30.00 -11.74 -7.05 7

33.55 3.35 2.01 2

* x 10-19 C

** x (1.665 x 10-19 C)

Ernest Rutherford (1871 - 1937)

Worked with:Hans GeigerErnest Marsden

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 himsee if any alpha particles can be scattered through a large angle?” I maytell you in confidence that I did not believe that there would be, sincewe knew the alpha particle was a very fast massive particle, with a greatdeal of energy, and you could show that if the scattering was due to theaccumulated effect of a number of small scatterings the chance of an alphaparticle being scattered backward was very small.

Gold Foil Experiment

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