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Joseph John Thomson-Atomic Theory
13
Transcript
Joseph John Thomson
The Electron
Discovery of Electron
- In 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces.
- He was the first to suggest that the fundamental unit was over 1000 times smaller than an atom, suggesting the subatomic particles were known as electrons.
Electron by Accident
- Discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube
- The deflection of the rays by electrically charged plates and magnets was evidence that he calculated to having a very large value for the charge-to-mass ratio.
J. J. Thomson
Atomic theory
1.An atom consists of a sphere of positive charge with negatively charged electron embedded in it,
2.The positive and the negative charges in an atom are equal in magnitude, due to which an atom is electrically neutral. It has no over all negative or positive charge.
Thomson's experiment(s)
- Experiment 1: The cathode rays are negatively charged so they should be deflected by electrostatic forces, and when exposed to this force they were deflected.
- Experiment 2: The cathode rays are negatively charged so they should be deflected by magnetic force in a way that shows that they're negative, and they were deflected that way.
- Experiment 3: The charge to mass ratio that he found suggested that the particle was thousands of times smaller than a hydrogen atom. By running the third experiment, Thomson was able to determine e/m, which is the mass to charge ratio of a particle.
British Physicist
Facts
- In 1884 he became Cavendish Professor of Physics.
- In 1906, he was awarded a Nobel Prize for Physics.
- In 1908 he was knighted and appointed to the Order of Merit in 1912.
- In 1918 he became Master of Trinity College, Cambridge, where he remained until his death.
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