7.15 describe the results of Geiger and Marsden’s experiments with gold foil and alpha particles

Previously, the ‘plum pudding‘ model of an atom was believed; atoms were spheres (+ve) with tiny electrons (-ve) inside.
If this was true, the alpha particles would’ve gone through the sheet of gold.


To test this theory, Geiger and Marsden set up an experiment:


  • A beam of alpha particles was aimed at very thin gold foil
  • Passage through foil was detected
  • Scientists expected particles to pass straight through. HOWEVER

Some alpha particles passed through, but others deflected the foil at different angles, and some came straight back.

  • Realised that positively charged alpha particles were being repelled and deflected by a tiny concentration of positive charge in the atom.

Alpha particles travelled straight through the electron shells without changing direction.

If alpha particle gets close to nucleus (+ve), it repels and changes direction.

The closer it got to the nucleus, the more it changed direction.


Replaced with Rutherford’s nuclear model of the atom.

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