Rutherford did his scatter experiment to disprove Thomson's Plum Pudding Model. Rutherford shot helium nuclei at a sheet of gold and expected the particles to all go straight through to a sensor. The reason he expected this was because Thomson said that atoms are mostly made of empty space. Not all the particles went through the gold sheet, a lot of them actually reflected back to him. This meant that atoms aren't entirely empty space and something had to deflect the helium nuclei
