Rutherford’s gold foil experiment goes by the official title of the Geiger-Marsden Experiment.  Hans Geiger and Ernest Marsden conducted the experiment under the direction of Ernest Rutherford in 1909 and the University of Manchester.  A beam of alpha particles emitted by radium bromide gas was concentrated on a thin sheet of gold foil.  The thickness of the foil was recorded as 6 * 10-8, which is only about 200 atoms thick.   The apparatus for the experiment can be seen in the figure below.

    At the time that the experiment was conducted, the plum pudding model was the accepted visual explanation of the internal structure of the atom.  The model was theorized by J.J. Thompson, the man who discovered the electron in 1897.  His idea was that inside the atom existed electrons surrounded by a plethora of positive charge that would balance out the negative charge of the electrons, thus resembling a plum pudding.  Based on this model, it was hypothesized that when the alpha particles were directed at the gold foil, they would deflect very little, a few degrees at most.  Instead, the particles deflected at very large angles.  Some even bounced straight back at the alpha particle source.  This totally shocked the scientists conducting the experiment.  Rutherford said, “It was almost as incredible as if you fired a fifteen inch shell at a piece of tissue paper and it came back to hit you.”
    From the results of the experiment, Rutherford concluded that the atom was composed of a small positive charge that had caused the alpha particles to repel at such extreme angles.  The rest of the atom is made up of mostly open space.  In 1913 mathematician Niels Bohr used Rutherford’s ideas to develop the Bohr model.