Developing models of atoms

• John Dalton

  • published his ideas about atoms in 1804
  • thought that all matter was made of tiny particles called atoms
  • imagined atoms as tiny spheres that could not be divided
  • uses his atomic model to explain the properties of gases and the formulae of compounds
• JJ Thompson

  • 1897
  • carried out experiments and discovered the electron
  • the mass of an electron was much smaller than the mass of an atom
  • electrons must be subatomic particles
  • plum pudding model of atom
  • atom is a ball of positive charge with negative electrons embedded in it
• Ernest Rutherford

  • 1911
  • used results from an experiment to test the plum pudding model
  • positively charged alpha particles were fired at thin gold foil
  • most alpha particles went straight through the foil
  • a few were scattered in different directions
  • suggested new model - nuclear model
  • the mass of an atom is concentrated at its centre, the nucleus
  • the nucleus is positively charged
  • nucleus contained small particles - protons
  • each proton has a small amount of positive charge
• James Chadwick

  • 1932
  • found evidence for the existence of particles in the nucleus with mass but no charge
  • these particles are called neutrons
  • led to another development of the atomic model which is still used today