A Timeline of the Atom -400BC...0 1800 1850 1900 1950 400 B.C.Democritus:idea of an atom 1808 John Dalton introduces his atomic theory. 1820 Faraday:charge/mass ratio of protons 1885 E.Goldstein:discovers a positively charged sub-atomic particle 1898 J.J.Thompson finds a negatively charged particle called an electron. 1909 Robert Millikan experiments to find the charge and mass of the electron. 1911 Ernest Rutherford discovers the nucleus of an atom. 1913 Niels Bohr introduces his atomic theory. 1919 The positively charged particle identified by Goldstein is found to be a proton. 1920s Heisenberg,de Broglie,and Schrodinger. 1932 James Chadwick finds the neutron. 1964 The Up,Down,and Strange quark are discovered. 1974 The Charm quark is discovered. 1977 The Bottom quark is discovered. 1995 The Top (and final)quark is discovered. -2A Timeline of the Atom 400 BC 0 1800 400 B.C. Democritus: idea of an atom 1808 John Dalton introduces his atomic theory. 1820 Faraday: charge/mass ratio of protons 1885 E. Goldstein: discovers a positively charged sub-atomic particle 1898 J. J. Thompson finds a negatively charged particle called an electron. 1909 Robert Millikan experiments to find the charge and mass of the electron. 1911 Ernest Rutherford discovers the nucleus of an atom. 1913 Niels Bohr introduces his atomic theory. 1919 The positively charged particle identified by Goldstein is found to be a proton. 1920s Heisenberg, de Broglie, and Schrödinger. 1932 James Chadwick finds the neutron. 1964 The Up, Down, and Strange quark are discovered. 1974 The Charm quark is discovered. 1977 The Bottom quark is discovered. 1995 The Top (and final) quark is discovered. ...... ....... 1850 1900 1950 II-2