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The History of the Atom
Joseph John Thomson Model

"...we have in the cathode rays matter in a new state, a state in which the subdivision of matter is carried very much farther than in the ordinary gaseous state: a state in which all matter-that is, matter derived from different sources such as hydrogen, oxygen, etc.-is of one and the same kind; this matter being the substance from which the chemical elements are built up."
-J.J. Thomson (1897) in "Cathode Rays," Philosophical Magazine 44, 295.)

On April 30, 1897, Joseph John Thomson announced that cathode rays were negatively charged particles which he called 'corpuscles.' He also announced that they had a mass about 1000 times smaller than a hydrogen atom, and he claimed that these corpuscles were the things from which atoms were built up. This hypothesis was not generally accepted until 1899 when an Irish physicist named George Francis FitzGerald proposed that the "corpuscles" Thomson spoke of were actually free electron patricles. Thomson designed the famous "plum pudding model" shown to the right.

The Plum Pudding Model

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