In his famous gold foil experiment in 1911, Rutherford and his team fired alpha particles (positively charged helium nuclei) at a thin sheet of gold foil. They expected the particles to pass straight through, as the prevailing model of the atom at the time suggested a diffuse, positively charged "pudding" with electrons embedded in it.
However, the results were surprising:
* Most of the alpha particles passed straight through the foil, as expected.
* Some particles were deflected at small angles.
* A very small number were deflected at very large angles, even bouncing back in the direction they came from.
Rutherford's interpretation of these results was revolutionary:
* The atom is mostly empty space. This explained why most particles passed straight through.
* A tiny, dense, positively charged center exists within the atom. This explained why some particles were deflected and a few were even bounced back. Rutherford called this center the nucleus.
His findings led to the development of the nuclear model of the atom, which is still the basis of our understanding of atomic structure today.
