J.J. Thomson was an English scientist who started his work in about 1890. His experiments with cathode ray tubes lead him to discover the electron. It was known the charge of the “ray” inside of the tube was negative. He slid a magnet across the tube and the charge was bent away by the magnet, proving the ray and negative charge are inseparable from each other. He proved that the charge of the ray was indeed negative by setting up a cathode ray tube with a positive anode and negative cathode. The negative cathode repelled the rays and since negative repels negative, he proved that the rays were made up of negatively charged particles. He also stated the charge to mass ratio of an atom is extremely large, and the charge came from particles within the atom itself. Because the ratio is so large he deducted that the particles carried an extremely small charge. We now know that the charge of an electron is 1.6021765 × 10−19 coulomb (click for definition).


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http://www.daviddarling.info/encyclopedia/T/Thomson_Joseph.html

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http://www.sciencewithmrmilstid.com/category/physics/matter-properties-of-matter/atomic-structure/

Thomson's "plum pudding" model consists of electrons and a positively charged jelly like substance. He stated that the entire electron was neutral. In this picture there are 13 electrons and 13 little plus signs representing that this particular atom has 13 electrons and the charge of the jelly like substance is +13, counterbalancing the electrons.

Positives of Thomson's Model-
It was the first model that suggested atoms had internal structure.

Negatives of Thomson's Model-
Thomson was not aware that protons and neutrons existed, let alone that they were contained in a nucleus, thus they are not in his model. We now know that they exist and they are included in newer models.