JJ Thompson – Discovery of Electrons

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Presentation transcript:

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

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

- 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

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

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

Thomson’s Experiment voltage source ON - OFF +

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

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

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

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

Thomson thought that mass was evenly distributed throughout the atom -

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

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

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