History of The Atom

• What did John Dalton describe atoms as


  Solid spheres that make up elements
• What did JJ Thompson conclude


  Atoms were not solid spheres.
• What did JJ Thompson discover in 1897


  Electrons because measurements of charge and mass showed that negatively charged particles exist
• What was JJ Thompson's model


  The Plum Pudding Model. Atom as a ball of positive charge with electrons stuck in it
• What was Ernest Rutherford's experiment

  Alpha particle scattering experiment

  1. they fired positively charged alpha particles at a thin sheet of gold
  2. they expected the particles to pass straight through but some were deflected more than expected
• What was Rutherford's model


  The Nuclear Model. Tiny, positively charged nucleus in the centre, where mass is concentrated. 'cloud' of negative electrons surrounding the nucleus so most of atom is empty space.
• What happened to alpha particles when they came near the concentrated, positive charge of the nucleus


  They were deflected
• What did Bohr discover


  A 'cloud' of electrons would cause the atom to collapse so Bohr suggested they were in shells
• What was Bohr's theory of atomic structure


  Electrons orbit the nucleus in fixed shells
• Who discovered protons and how


  Rutherford showed that the nucleus could be divided into smaller particles with the same charge as a hydrogen nucleus
• Who discovered neutrons


  James Chadwick
• What was the order of discovery for each subatomic particle


  Electron, Proton, Neutron