Answer
Rutherford shot positively charged alpha particles at a very thin sheet of gold. A very small percentage of these were deflected or reflected backwards.
Work Step by Step
This would disprove the plum pudding model of the atom. The plum pudding model did not allow for the large empty space that would allow most of the particles to pass through. Rutherford correctly concluded based on the results that electrons must orbit a very dense nucleus.
