1.1 - Models of Atomic Structure

• history of the atom scientists in order

  democritus

  dalton

  thomson

  rutherford

  bohr

  chadwick
• democritus' theory of the atom

  came up with idea that everything is made of small indivisible particles called atomos

  atomos had different shapes

  didn't do any tests so no one believed his theory
• dalton's theory of the atom

  all elements and compounds are made of atoms which are indivisible

  all atoms of a given element are identical and have the same mass

  atoms of different elements have different masses

  atoms can combine to form molecules or compounds

  all molecules of an given compound are identical
• J.J. thomson's discovery about the atom

  discovered electrons and came up with the plum pudding model: atoms were tiny balls with of positive material with electrons embedded in them
• rutherford's experiment

  fired alpha particles at thin gold foil, most went straight through, some were scattered and some rebounded from the foil
• rutherford's discovery from his experiment

  atoms have a small positive nucleus (due to protons) surrounded by empty space where there are negative electrons

  atoms have the same number of protons and neutrons

  came up with the nuclear model of the atom
• bohr's discovery

  came up with idea that electrons exist in energy levels in a circular orbit

  electrons can move up and down energy levels if they get 'excited'

  current model of the atom
• chadwick's discovery

  couldn't understand why He had a mass of 4 and not 2 (since it had 2 protons)

  studied effects of bombarding Be with alpha particles - produced radiation with no charge that released protons when fired at wax

  discovered neutrons
• thomson's experiment

  was studying conduction of electricity by gases

  connected 15000V across terminals of a tube with air and glass walls glowed green

  rays could be deflected by electric fields - when they passed through charged plates they bent towards the positive plate so rays were negatively charged

  rays consisted of tiny negative particles (electrons)