Sir Joseph John "J. J." Thomson
R.V:Sir Joseph John "J. J." Thomson a British physicist.he was born 18 December 1856 and died on the 30 August 1940.
In 1897 he discovered a electron in a series of experiments.he did it by doing a cathode ray experiment that led to evidence of bodies much smaller than atoms that he calculated as having a very large value for the charge to mass ratio and having a negative charge.As he knew that atoms on the own had no charge so they were neutral, this meant that in the atom there must also be a positive charge present to balance the negative charge of the electrons.So in 1904 Thomson suggested a model that later called “the plum putting model” is of a atom as a sphere of positive matter in which electrons are positioned and embedded so the charges were balanced.This model helped explain the nature of electricity, how metals can conduct electricity and why some elements form positive ions. Thomson’s last important experimental program was focused on determining the nature of positively charged particles. This led to development of the mass spectrograph.He also assisted, Francis Aston,by developing Thomson's instrument further and a improved version that made them able to discover isotopes. Sir Joseph John "J. J." Thomson’s model and theory of the atom structure differs from Daltons.This is due to that Thomson’s theory of a atom was a sphere of positive matter in which electrons are positioned and embedded so the charges were balanced. Daltons theory never acknowledged the fact that the atomic structure consisted of protons nor electrons. |
M.F:Thomson held that atoms are uniform spheres of positively charged matter in which electrons are embedded. Popularly known as the plum-pudding model, it had to be abandoned (1911) on both theoretical and experimental grounds in favour of the Rutherford atomic model, in which the electrons describe orbits about a tiny positive nucleus.
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