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460
Democritus
Nothing exists except atoms and empty space; everything
else is opinion.” - Democritus 460–370 B.C. -
Issac Newton
Proposed a mechanical universe with small solid masses in motion. -
John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
JJ Thompson
Discovered electrons using Cathode Ray Tube experiment. He also determined the charge to mass ratio (e/m) of an electron =1.759 x 10^ 8 coulombs/gram. -
R.A Millikan
He determined the charge (e=1.602 x 10 -^19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron in his oil drop experiment -
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. -
Neils Bohr
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons. -
De Broglie
Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein. -
Heisenberg
Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle. -
Schrodinger
Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. -
James Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.
