how were alpha particles used and founded before the gold foil experiment if we didn’t know at that time that protons and neutrons existed and we didn’t know the charge of alpha particles

Question

I understood most of the rutherford experiment except how did rutherford know the properties of alpha particles when we didn’t know about protons and neutrons .

In: Chemistry

Answer 1

Rutherford knew the properties of alpha particles but he didn’t know about their internal structure (because neutrons and protons had yet to be discovered.) But he knew they had an atomic weight of 4. So from that he deduced that they were similar to a helium atom with no electrons, and proved this in 1907 – he collected alpha particles in a glass tube, then added an electric discharge. The spectrum of light emitted by the resulting gas matched that of helium – so, if alpha particles + electrons make helium gas, well then alpha particles must have a positive charge