Chemistry Helpers
Atomic Theory Definitions Atomic Theory History
Atomic Theory History


400 BC           Democritus                Proposes the idea of the atom
1807               John Dalton                Founder of modern atomic theory
                                                            His model survived for almost 100 years
1885               J.J. Thomson Discovery of the “proton”
1896               Henri Becquerel        Discovery of Radioactivity
1897               J.J. Thomson Discovery of the “electron”
1903               J.J. Thomson “Plum-pudding” model
1909               Ernest Rutherford      The Gold Foil Experiment
1911               Ernest Rutherford      Rutherford’s model of the atom
1913               Niels Bohr                  Electrons exist in discrete energy levels
1923               Robert Millikan          The Oil Drop Experiment
                                                            Discovered the charge of an electron
                                                            Discovered the mass p+ = 1836 the mass of e-
1923               Erwin Schrodinger    Wave Particle duality
1925               Erwin Schrodigner    Quantum Mechanical Model of the Atom
1932               James Chadwick      Discovery of the “neutron”

1945               Wolfgang Pauli          Pauli Exclusion Principle

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