The development of the model of the atom

• • Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided
• • The discovery of the electron led to the plum pudding model
  • The plum pudding model was developed in 1897 by JJ Thompson
  • The model suggested that the atom is a ball of positive charge with negative electrons embedded
• • The alpha particle scattering experiment shows that the plum pudding model was wrong
  • The alpha particle scattering experiment was developed in 1909 by Rutherford
  • A few particles deflected backwards from the nucleus
  • The mass of the atom is concentrated at the centre and is charged - nucleus
  • The atom is mostly empty space because a negative electrons surrounds nucleus
• • Bohr suggested that all electrons were contained in shells
  • If electrons were around the nucleus, the electrons would be attracted to the nucleus and cause the atom to collapse
  • Bohr suggested that electrons orbit nucleus at fixed shells
• • Later experiments showed that nucleus could be divided into smaller particles
  • These particles were called protons
• • James Chadwick discovered the neutron in 1932 in the nucleus
  • This was 20 years after the nucleus was an accepted scientific idea
  • The discovery of the nucleus led to the nuclear model of the atom