Geiger-Marsden Experiment

Some important differences between the electrons and the nuclei: (1) they are far less massive, and (2) their charge is far less concentrated. Both these combine to mean the alpha particle will not deflect off an electron, both because of (1) conservation of momentum and (2) the magnitude of the electrostatic force will be far less than a localised nucleus (of +79e charge).

You would not expect the alpha particle to deflect off an electron for this reason.

It would be like expecting a cricket ball to be deflected backwards when passing through a swarm of flies. The nucleus, on the other hand, is far more massive than the alpha particle, and is more like a cricket ball Vs. a car.

Thank you for your time in writing your reply.

However, if anything, since alpha particles (positive) and electrons (negative) have opposite charges, shouldn't the electron pull the alpha particle towards it instead of deflecting it?

That's is true, but the argument is not really affected when you replace repulsion with attraction. The electrons are too dispersed to exert a strong electrostatic attraction to the alpha particle, and their mass is too low for any deflection of them in the vicinity of the alpha particle to significantly change the momentum of the particle itself.

Also, while it is okay to consider the nucleus a localised bunch of positive charges, it is not generally okay to think of the electron as a disperse bunch of pointwise negative charges. Think of them as clouds that surround the nucleus subject to some certain rules (which arise from quantum mechanics). So the concept of an alpha particle striking an individual electron like a billiard ball does not really exist.

Thanks!

If I did the experiment but using beta particles instead of alpha particles, would you see the all of the beta particles attract to the gold nuclei or would you see some of them get deflected by the surrounding gold electrons before they reach the nucleus?

(This question was actually part of my preparation for A Level Chemistry, but I thought it'd be better to ask it in the Physics forum).

(...)
However, why didn't the few alpha particles which hit an electron (of the gold atom) attract, or at least have an effect on one another? Is this to do with the fact that an alpha particle is +2 whereas an electron is only -1?
(...)

Electrons are attracted by the positive charge of the nucleus. They are in bound states for that reason.

Electrons also have no known inherent "size" or volume. It is quite possible that they are point-like, but that doesn't matter. The interaction with an alpha particle is still via the electric force, and since electrons have charge, they can interact with the alpha particle via this force. The important thing is not a difference in size (the electron "cloud" or wavefunction is spread much farther over space than the nucleus's), but a difference in mass.

So if the difference in mass between alpha particles and electrons would not be so huge, they would attract each other, is that right?

but what about the quantity?

if the numbers of electrons close to an alpha particle is great, would they not achieve a mass in addition which is great enough to cause an attraction?

Based on the mass ratios, what would you expect? Electron Vs. electron, one basically stationary, one moving at about the speed of light. The mass ratio is the key difference here.

If you have very large object (alpha) tearing through a cloud of light objects (electrons), it won't be deflected. But it can be deflected from something slightly larger than it (nucleus). The beta particle, on the other hand, can quite readily be deflected by atomic electrons, and will readily transfer its kinetic energy to them via the collision. That means it will slow down after enough collisions (and probably ionise a few gold atoms on its way through).

(...) The difference is the extent to which that force of attraction is able to change the radiation particle's momentum. (...)

The electron mass is ~1/1800 a nucleon mass, which is far too big a difference, and they do not group together in the way you describe.

May I ask, shouldn't the gold in the gold foil be ions anyway instead of gold atoms, thanks to metallic bonding?

I am so sorry, but I don't understand this part of your explanation. Could you be a bit clearer, please?

Previously you wrote that "electrons are attracted by the positive charge of the nucleus", so they are in a "bound state". But one of the riddles in atomic physics is why these electrons do not fall into the nucleus and move on their electron paths instead. Do this electron paths (and thus the electrons) have a great distance to be attracted by the positive charge of the nucleus completely?

May I ask, shouldn't the gold in the gold foil be ions anyway instead of gold atoms, thanks to metallic bonding?