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Democritus
Democritus created the atomic theory -
John Dalton
he said that All atoms of a given element are identical in mass and properties. -
JJ Thomson
In 1897 he showed that cathode rays, radiation emitted in a low pressure glass tube when a voltage is applied between two metal plates, consist of particles, electrons, that carry electricity -
Robert Millikan
He determined the charge on electrons -
Ernest Rutherford
the total mass of an atom is concentrated in a nucleus. by doing this he gave birth to the nuclear model -
Niles Bohr
The discoveries of the electron and radioactivity at the end of the 19th century led to different models for the structure of the atom. In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. Bohr's theory could explain why atoms emitted light in -
James Chadwick
he discovered the exsitsnance of a neutron in a atom