history of the atom

• how has the theory of atomic structure changed over time?


  1. at the start of the 19th century John Dalton described atoms as solid spheres and said that different spheres made up the different elements
  2. in 1897 J J Thompson concluded from his experiments that atoms weren't solid spheres.
  3. the plum pudding model showed the atom as a ball of positive charge with electrons stuck in it
• what did Rutherford show was wrong?


  the plum pudding model
• how did Rutherford show that the plum pudding model was wrong?


  by conducting the alpha particle scattering experiment. this was where they fired positively charged alpha particles at an extremely thin sheet of gold
• what did the alpha particle scattering experiment show?


  showed that some of the alpha particles were deflected by more than expected, and a small number were deflected backwards, implying that the plum pudding model was incorrect.
• what did Rutherford do after the alpha particle scattering experiment?


  he created the nuclear model of the atom which showed positvely charge nucleus at the centre and a cloud of negatively charged electrons surrounding the nucleus.
• what did Neils Bohr's nuclear model suggested?


  suggested that all the electrons were contained in shells
• what do further experiments how?


  the existence of protons