In 1911, Rutherford conducted his famous gold foil experiment. In this experiment, he fired alpha particles (positively charged particles) at a thin sheet of gold foil. He observed that most of the alpha particles passed straight through the foil, but some were deflected at large angles, and a few even bounced back.

This unexpected result led Rutherford to propose the nuclear model of the atom. He concluded that the atom must have a small, dense, positively charged center called the nucleus, which contained most of the atom's mass. The electrons, being negatively charged, would orbit the nucleus at a relatively large distance.

Rutherford's discovery revolutionized our understanding of the atom and paved the way for further research in nuclear physics.