What did Rutherford's gold-foil experiment tell about the atom?
Rutherford's gold foil experiments (and other metal foil experiments) involved firing positively charged alpha particles at a piece of gold/metal foil. The alpha particles that were fired at the gold foil were positively charged. Most of the time, the alpha particles would pass through the foil without any change in their trajectories, which is what was expected if JJ Thomson's plum pudding model of the atom was correct. However, occasionally the alpha particles would be deflected to some degree, and sometimes an alpha particle would bounce back directly toward the experimenter. Rutherford likened this to firing a 15-inch artillery shell at a sheet of tissue paper and the shell came back to hit you.
For perspective, this is a picture of a 15-inch artillery shell. It was used in both WW I and WW II. It weighed 879 kg (1938 lb).
In order for the alpha particles to be deflected, they would have to hit or come near to a positively charged particle in the atom. These experiments led Rutherford to describe the atom as containing mostly empty space, with a very small, dense, positively charged nucleus at the center, which contained most of the mass of the atom, with the electrons orbiting the nucleus.