Atomic Structure

• how has the atomic structure changed over time?

  • John Dalton - described atoms as spheres
  • JJ Thomson - plum pudding model
  • Ernest Rutherford - the nuclear model
  • Neils Bohr - a more developed nuclear model
• Plum pudding model 


  a ball of positive charge with electrons stuck in it - showed that there were different charges and masses in an atom so there must be particles even smaller
• nuclear model

  • alpha particle scattering experiments - fired positively charged alpha particles at an extremely thin sheet of gold and some were deflected backwards which proved the PPM to be wrong
  • a tiny positively charged nucleus at the centre and a cloud of negative electrons surrounds the nucleus - most of the atom is empty space
• developed nuclear model

  • bohr found that electrons travelled around in fixed shells and each shell is fixed distance from the nucleus
  • supported by many experiments and it helped other scientists observations at the time
• neutron


  about 20 years after the idea of the nucleus, in 1932, James Chadwick proved the existence of the neutron which explained the imbalance between the atomic and mass numbers