# Electrons and protons

1. Jun 16, 2010

### Kat007

1. The problem statement, all variables and given/known data
What is stopping electrons from collapsing onto protons of the atom? And why doesn't the electron go closer to the nucleus than the 1s orbital?

2. Relevant equations

3. The attempt at a solution

2. Jun 16, 2010

### stevenb

Perhaps electrons are like those girls that just want to be friends and not lovers.

Or, more likely, electrons obey the Schrodinger equation, and the 1s orbital is the lowest energy bound state that is a valid solution. Basically, bound states are quantized, and as much as negative is attracted to positive, electrostatic force can not overcome quantum mechanical rules.

There is probably a more elegant explanation from the point of view of quantum field theory. I don't know it, but I'd like to hear it if someone else does.

3. Jun 16, 2010

### Kat007

Well, mathematically it is the lowest energy level, but I would have thought there is a some reason for it. Is something repelling the electron from nucleus also?

4. Jun 16, 2010

### Ygggdrasil

You can understand this issue from the perspective of the Heisenberg uncertainty principle. The question you're asking is why is a wavefunction where the electrons are localized to the nucleus not valid. In such a wavefunction, the electrons are very highly localized and therefore the uncertainty in the position of the electrons is low. In order to not break the Heisenberg uncertainty principle, the electrons must have a large uncertainty in their momentum. However, this means that a significant portion must have very large momenta, which would tend to move the atoms away from the nucleus. This, however, is incompatible with a tight positioning of the electron right on top of the nucleus.

Therefore, the uncertainty principle causes a sort of quantum repulsion, that keeps electrons from being too tightly localized near the nucleus.

5. Jun 16, 2010

### Kat007

That is an interesting idea actually, didnt think of it this way.
Also what about if we think from the point of subatomic particles? Is there any repulsion between some of the particles making up the electron and the nutrons/protons?

6. Jun 16, 2010

### dulrich

I think Ygggdrasil doesn't mean repulsion in any electromagnetic sense, but that in a sense it is repulsed from itself -- or spread out like a wave and can't be contained in a way that is stable.

All subatomic particles are like this, including protons and neutrons, but the amount of spread is based on mass. The lighter the particle, the more spread. An electron is spread out about the size of the atom, a proton or neutron is spread out about the size of the nucleus.

7. Jun 16, 2010

### Kat007

Yes I think I understood Ygggdrasil's explanation about Heisenberg uncertainty principle, good way of thinking about it :).
The electromagnetic sence was a separate question/ idea. Is there any electromagnetic repulsion between the nucleus and electrons if we go down to subatomic particles or am I making things up now? :) Just wondering..

8. Jun 16, 2010

### dulrich

The electron is an elementary particle, so it has no parts. The electron is actually attracted to the proton (which is why the electron surrounds the nucleus) and does not interact with the neutron.

But both the proton and neutron are composed of quarks (which are elementary) which are have positive and negative charges. So you could argue that there is some electromagnetic repulsion occuring between the electron and the d quarks, but at that (sub-nuclear) level the strong nuclear force dominates the discussion.

9. Jul 1, 2010

### mhmd

I always thought it was the centrifugal force, like how the earth spins around the sun. :/

10. Jul 2, 2010

### Char. Limit

Well, firstly, I believe the centripetal force is meant. However, this force fails to explain why an electron requires certain energy levels, and cannot go between them.

I think.

11. Jul 18, 2010

### Kat007

Last edited by a moderator: Apr 25, 2017
12. Jul 18, 2010

### Kat007

Exactly, what is holding it between these levels and not elsewhere? I mean these levels are so well defined! I just don't get it. My only idea, like we said before, yes it is attracted to the positive charge of proton, but repelled by something else (as Dulrich suggested by the d quarks?). But how do the orbitals come about?

Another interesting thing that astonished me when i first heard it is electron tunnelling. Extraordinary I think! How on Earth does it manage that?! And it does! I saw that STM at work with my own eyes! ;)

13. Jul 18, 2010

### vela

Staff Emeritus
It's the wave nature of the electron. The orbitals are standing-wave solutions. It's like a vibrating string with fixed ends. Only certain wavelengths satisfy the boundary conditions, resulting in only certain allowed energies. Essentially the same thing happens with the electron around a proton, but the math is much more complicated.

14. Jul 19, 2010

### Ygggdrasil

Also remember that in the modern picture of an atom (as opposed to the Bohr model), while electrons have discrete, well separated energies, these energies do not correspond to discrete fixed radii. The electrons are not orbiting the nucleus with a fixed radius but rather they are moving around the nucleus within a certain area (defined by the wavefunction of the electron). These wavefunctions are associated with different average distances from the nucleus (and the average distances increase with increasing energy), but the distance of the electron from the nucleus is still a continuous value.

15. Jul 19, 2010

### Dickfore

The Heisenberg Uncertainty principle.