Model of the atom

• Thomson's plum pudding model

  • In 1897, an English physicist called J. J. Thomson discovered electrons.
  • He modelled the atom as a 'plum pudding' - a ball of positive charge (dough), with negatively charged electrons (currants) mixed in with the 'dough'.

  
• The modern model

  • Niels Bohr discovered that electrons orbit (fly around) the nucleus at fixed distances.
  • In 1932, James Chadwick discovered that some particles in the nucleus have no charge at all. He called them neutrons.

  
• Rutherford's nuclear model

  • In 1909, Ernest Rutherford discovered that alpha particles could bounce back off atoms.
  • He concluded that an atom's mass is concentrated in the atom's centre. This was called the "nucleus" and it contained positively charged particles called protons.