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Concept
Plum pudding model
Summary
The plum pudding model is one of several historical scientific models of the atom. First proposed by J. J. Thomson in 1904 soon after the discovery of the electron, but before the discovery of the atomic nucleus, the model tried to explain two properties of atoms then known: that electrons are negatively charged particles and that atoms have no net electric charge. The plum pudding model has electrons surrounded by a volume of positive charge, like negatively charged "plums" embedded in a positively charged "pudding".
It had been known for many years that atoms contain negatively charged subatomic particles. Thomson called them "corpuscles" (particles), but they were more commonly called "electrons", the name G. J. Stoney had coined for the "fundamental unit quantity of electricity" in 1891. It had also been known for many years that atoms have no net electric charge. Thomson held that atoms must also contain some positive charge that cancels out the negative charge of their electrons. Thomson published his proposed model in the March 1904 edition of the Philosophical Magazine, the leading British science journal of the day. In Thomson's view:
the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...
Thomson's model was the first to assign a specific inner structure to an atom, though his original description did not include mathematical formulas. He had followed the work of William Thomson who had written a paper proposing a vortex atom in 1867, J.J. Thomson abandoned his 1890 "nebular atom" hypothesis, based on the vortex theory of the atom, in which atoms were composed of immaterial vortices and suggested there were similarities between the arrangement of vortices and periodic regularity found among the chemical elements. Thomson based his atomic model on known experimental evidence of the day, and in fact, followed Lord Kelvin's lead again as Kelvin had proposed a positive sphere atom a year earlier.
Official source
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