A Timeline of the Atom ←—400BC... 1800 1850 1900 1950 -450 Empedocles-earth,air,fire,water -400 Democritus:idea of an atom;is water like sand:smooth from afar,coarse up close? atoms had no mass,just filled space 1661 Robert Boyle:Disputes 4 element theory;postulates an element is a substance that can not be reduced into simpler substances 1808 John Dalton postulates that atoms have weight and combine to form substances 1811 Amadeo Avogadro;Postulates that compounds are formed from molecules. 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 Heisenburg,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. -10A Timeline of the Atom 400 BC 0 1800 -450 Empedocles- earth, air, fire, water -400 Democritus: idea of an atom; is water like sand: smooth from afar, coarse up close? atoms had no mass, just filled space 1661 Robert Boyle: Disputes 4 element theory; postulates an element is a substance that can not be reduced into simpler substances 1808 John Dalton postulates that atoms have weight and combine to form substances 1811 Amadeo Avogadro; Postulates that compounds are formed from molecules. 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 Heisenburg, 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. ...... ....... 1850 1900 1950 I-10