flibber
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I am told that most of an atom is empty space, so most of the alpha particles went straight through the gold foil. However, a very small minority of the alpha particles were deflected by the small part of the atom called the nucleus, which is positively charged.

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?

Also, what happens if you are able to remove a proton from a hydrogen-1 atom?
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mik1a
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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.
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flibber
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(Original post by mik1a)
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?
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mik1a
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(Original post by flibber)
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.
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flibber
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(Original post by mik1a)
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).
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mik1a
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(Original post by flibber)
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).
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).
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Kallisto
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(Original post by flibber)
(...)
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?
(...)
Do you ask why the alpha particles do not interact with the electrons of an atom, although they have two different charges?

After the Bohr model there are three possible answers in my opinion:

1.) the electrons are in movement on their electron paths with a certain high velocity. This movement may work as a centrifugal force which counteracts attractions. That could be one of the reasons too why electrons are not attracted by the positive charge of the nucleus.

2.) As the electrons have a high velocity during movement, they are able to change their position very quickly (on their paths of course), thus it is unlikely that an alpha particle and an electrons hit each other at the same time.

3.) Another explanation is the proportion: Just hypothetically the atom has the size of a football stadium, compared to that the nucleus has the size of a ball in the centre circle! and an electron is still smaller... that is to say there is great free space, no matter how many electrons exist in a single atom (in terms of a gold one its 79). Thus an alpha particle can come get through an atom without to interact with a single electron so easily. This would not lead to an attraction as well.
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mik1a
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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.
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Kallisto
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(Original post by mik1a)
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?
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mik1a
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(Original post by Kallisto)
So if the difference in mass between alpha particles and electrons would not be so huge, they would attract each other, is that right?
They always are attracted, as they have opposite charge. The difference is the extent to which that force of attraction is able to change the radiation particle's momentum.

(Original post by Kallisto)
but what about the quantity?
I don't understand what this refers to

(Original post by Kallisto)
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?
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.
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flibber
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(Original post by mik1a)
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).
May I ask, shouldn't the gold in the gold foil be ions anyway instead of gold atoms, thanks to metallic bonding?
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Kallisto
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(Original post by mik1a)
(...) The difference is the extent to which that force of attraction is able to change the radiation particle's momentum. (...)
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?

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.
Yeah, it was just a silly thought experiment, no more.
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Kallisto
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(Original post by flibber)
May I ask, shouldn't the gold in the gold foil be ions anyway instead of gold atoms, thanks to metallic bonding?
Do you talk about the model where free electrons exist in outer shells? from this perspective, I would say that you are right, as the positive charges around these electrons are regarded as metal ions. but are these positive charges (metal ions) and electrons not the part of gold atoms? from this perspective you can talk about atoms too.
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mik1a
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(Original post by Kallisto)
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?
The electrons do not "fall" into the nucleus because their dynamics are not governed by Newton's 2nd law, i.e. you shouldn't think of them as particles in orbit of the nucleus. Their existence in bound states of the atom is governed by Schrodiner's equation.
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mik1a
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(Original post by flibber)
May I ask, shouldn't the gold in the gold foil be ions anyway instead of gold atoms, thanks to metallic bonding?
I suppose you can call them that. It will be an ionic lattice plus some free electrons.
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