How did Rutherford infer that the nucleus was very small?

Answer 1

In conclusion...

Rutherford's experiment involved a radioactive source emitting alpha particles (2 protons and 2 neutrons).

The radioactive source was aimed at a thin sheet of gold.

The main observation made was that a few alpha particles were repelled back the way they had come, and this was not expected. This was because the positively charged alpha particles (2 protons), by the laws of electrostatic repulsion, were repelled by the positively charged nucleus of the atoms in the gold.

He then made the final conclusion of that the small nucleus of an atom is central, has a large mass and positive charge.

So yes, the nucleus is small compared to the size of an atom, however it was mainly the fact that there is one concentration of positive charge (nucleus) in the atom that repelled the alpha particles that helped Rutherford to show the structure of an atom.

Answer 2

Most of the alpha particles that he shot through the atoms did NOT bounce back at him, but went straight through. He reasoned that if the nucleus were large, the alpha particles would bump into it and bounce back. Since that did not occur, he correctly suggested the nucleus was very small and did not occupy much space.

Answer 3

Jj Thomson