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465 BCE
Democritus
According to Democritus atoms were miniscule quantities of matter. Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms. -
John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
William Thomson
Used a CRT to experimentally determine the charge to mass ratio of an electron =1.759 x 10 8 coulombs/gram. -
Ernest Rutherford
Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus. -
Niels Bohr
proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities
