Models of Atomic Structure

1808 – Dalton proposes “Atomic Theory”
  • Each element is made of tiny particles called atoms.
  • Atoms of a given element are identical. Atoms of different elements are different in some fundamental way
  • Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative number and type of atoms.
1898-1903 – JJ Thomson (cathode ray experiment)
  • Found when high voltage is applied across the 2 metal nodes in the cathode ray tube a negatively charged beam was produced.
  • Led to the plum pudding model of the atom that consisted of a positively charged cloud with negative electrons embedded in it randomly.
1909 – Robert Millikan (oil drop experiment)
  • Determined charge and mass of electron using oil droplets between charged plates
1911 – Rutherfords metal foil experiment
  • Determined there must be a large positive mass at the center of the atom
1922 – Niels Bohr
  • Introduced idea of electron orbital shells
1932 – James Chadwick
  • Discovered neutrons