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Democritus
Democritus, a Greek philosopher, co-originated the thought that all matter is composed of indivisible elements. -
John Dalton
John Dalton developed a theory that matter is simply composed of atoms of different weights and is combined in ratios by weight. Also proposed that these atoms are spherical, and are in motion. -
J.J. Thomson
J.J. Thomson determined the charge to mass ratio of electrons -
Rutherford
Rutherford discovered alpha, beta, and gamma rays in radiation -
Quantum-Mechanical Model
In 1913, Neils Bohr, a student of Rutherford's, developed a new model of the atom. He proposed that electrons are arranged in concentric circular orbits around the nucleus. -
Niels Bohr
Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.
