Answer:
So originally, the plum pudding model by J.J Thomson is electrons (negatively charged) held in place by a proton (positively charged) cloud.
Alpha particles are positively charged made of 2 protons + 2 neutrons.
Rutherford's experiment where they beamed those positively charged alpha particles demonstrated that an atom was not a uniform cloud, instead the alpha particles that were deflected was the positively charged nucleus. The alpha particles would also pass through if it didn't hit the nucleus, or be slightly attracted to the negative charge on the electrons. But the overall idea is that Rutherford's experiment changed what the structure of the atom was by discovering that they have a positively charged nucleus due to the deflection of positively charged alpha particles.
