In Rutherford's famous experiment, he shot heavy, fast moving, positive alpha particles at a thin gold foil. Based on Thomson's plum pudding model of the atom, what did Rutherford expect to happen, and why?

Question

All the alpha particles would be deflected by the foil because of the even distribution of mass and charge throughout the atom.
All the alpha particles would pass straight through the foil because of the even distribution of mass and charge throughout the atom.
Most of the alpha particles would become embedded in the foil because they are attracted to the negative electrons in the atom.
Some of the alpha particles would be deflected and some would pass through because of the negative charge of the electron cloud.

Answer 1

Rutherford's expectations before conducting his experiment were primarily based on Thomson's plum pudding model of the atom, which posited that the atom was a diffuse cloud of positive charge with electrons embedded within it, similar to plums in a pudding.

Rutherford anticipated that, due to this even distribution of positive charge and mass throughout the atom, most alpha particles would pass through the gold foil with little or no deflection. He believed that only a small fraction of the alpha particles might be deflected at very small angles due to occasional interactions with electrons, but that the overall impact of the positive charge would not impede their passage significantly.

Given this understanding, the correct expectation based on Thomson's model would be:

All the alpha particles would pass straight through the foil because of the even distribution of mass and charge throughout the atom.

However, Rutherford's experiment revealed that a small number of alpha particles were deflected at large angles, leading to the conclusion that atoms have a small, dense nucleus, fundamentally altering our understanding of atomic structure.