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JJ Thompson – Discovery of Electrons

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1 JJ Thompson – Discovery of Electrons
Source of Electrical Potential Metal Plate Gas-filled glass tube Metal plate Stream of negative particles (electrons) J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58

2 A Cathode Ray Tube Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58

3 - Thomson’s Experiment + voltage source vacuum tube metal disks
J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out. vacuum tube metal disks

4 Thomson’s Experiment voltage source - + vacuum tube metal disks

5 - Thomson’s Experiment + voltage source
OFF + Passing an electric current makes a beam appear to move from the negative to the positive end

6 Thomson’s Experiment voltage source ON - OFF +

7 - Thomson’s Experiment + voltage source + -
OFF + + - By adding an electric field… he found that the moving pieces were negative.

8 J.J. Thomson He proved that atoms of any element can be made to emit tiny negative particles. From this he concluded that ALL atoms must contain these negative particles. He knew that atoms did not have a net negative charge and so there must be balancing the negative charge. Thomson proposed a model of the atom with subatomic particles (1903). This model was called the plum-pudding or raisin pudding model of the atom. J.J. Thomson

9 Thomson In 1910 proposed the Plum Pudding model
Spherical cloud of Positive charge Electrons In 1910 proposed the Plum Pudding model Negative electrons were embedded into a positively charged spherical cloud. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56

10 Plum-Pudding Model Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56

11 Thomson thought that mass was evenly distributed throughout the atom
-

12 Because, he thought the mass was evenly distributed in the atom
-

13 Explanation of Alpha-Scattering Results
+ - Alpha particles Nuclear atom Nucleus Plum-pudding atom Thomson’s model Rutherford’s model

14 The Rutherford Atom Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 323

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