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