Answer: Some of the heavy particles bounced off the foil, because there is a dense, positive area in the atom.
Explanation:
In Rutherford's experiment, he took a gold foil and bombarded it with alpha particles which carry positive charge. He thought that the alpha particles will pass straight through the foil, but to his surprise, many of them passed through, some of them deflected their path and a few of them bounced back.
From this he concluded that in an atom, there exist a small positive charge in the center. Due to this positive charge, the alpha particles deflected their path and some of them bounced straight back their path.
Thus he concluded that there is a dense, positive area in the atom.
