# Particles on the surface of an atom?

1. Sep 9, 2014

### tyogav

There are many particles inside an atom.

What particles make up the surface of an atom? When we see graphical illustrations of spherical atoms, what are we actually seeing?

2. Sep 9, 2014

### The_Duck

An atom has no surface. An atom is composed of a tiny nucleus and a cloud of electrons that surrounds the nucleus. The electron cloud has no definite edge or surface.

Whatever the illustrator decided to draw! If you are talking about atomic orbitals, these are showing of what regions of space have the highest probability to contain an electron.

3. Sep 9, 2014

4. Sep 9, 2014

### mattt

Usually, when drawing isolated atoms, they draw spheres, and you can guess the size of those spheres are meant to be the covalent-radius, the Van der Waals radius,...(one of the different definitions of radius of an atom).

As The_Duck pointed out above, atoms (and molecules) do not have an edge-surface or whatever you may call it. Also when they draw pictures of atomic (or molecular) orbitals, they are just some regions of space where some electrons have a given high probability ( normally 0.9 ) to be found in, but anyway there are infinitely many different regions of space where that same electron has a 0.9 probability to be found in, so they usually choose just one of those regions that are "nice" and "symmetric".

5. Sep 9, 2014

### Staff: Mentor

You see a layer of (probably) graphene in green and some atoms are drawn as reflective spheres.

6. Sep 9, 2014

### KL7AJ

You're actually seeing statistical data! The "surface" of an atom is actually a locus of points the outer electrons can occupy.

Imagine a spinning fan. On the whole, it looks like a solid disk, but there's space between the blades. In an atom, this is just a lot more extreme. If the nucleus was about the side of a grapefruit, the electron would be the point of a pin about 3000 miles away! (Actually the electron has NO size. :) )

Hope this helps...or not.

Eric

7. Sep 10, 2014

### Delta²

All the atoms consist of elementary particles, which elementary particles are (according to current theory) point particles, that is at a given time they occupy a single point in space. However these elementary point particles are in continuous movement, thats how we get the impression that they occupy some finite volume (like a spherical volume) in space.

8. Sep 10, 2014

### KL7AJ

Another way it can be described is electrons are infinitely small, but they have a large personal space. "))

9. Sep 10, 2014

### tyogav

Thanks everyone especially Delta2 and KL7AJ

Last edited: Sep 10, 2014
10. Sep 10, 2014

### ChrisVer

It has nothing to do with motion of electrons around the atom. What they mainly show is the probability of an electron existing in some region. And the solution is static...
At low energies however, at which you can't see the structure of an atom [electrons' energy mainly], the atom can be assumed as a solid sphere... That's what people thought in the past [before rutherford's experiment]...

11. Sep 10, 2014

### KL7AJ

This is why "obsolete" models can still be eminently useful. You can drill down this as deeply as you want...or not. :)

12. Sep 10, 2014

### Delta²

If the electrons didnt move at all and remain still then the probability to exist in some region would be zero except in a specific point where it would be 1.

13. Sep 10, 2014

### ChrisVer

except for that is impossible [it would have definite position and momentum], I didn't say it doesn't move. I'm saying that the probability to be found in some region has nothing to do with the electron moving (which would need pictures of it for several times to cover the probability- however the probability is there at any given time... that's why I called it static)

14. Sep 10, 2014

### Delta²

How can you say "it has nothing to do with electron moving" if the electrons dont move, there is no meaning talking about the probability to be found in a region of space, the only probability tha there is , is zero everywhere except a specific point.

There is no meaning talking about uncertainty principle, wave function or probability clouds or whatever unless the electron is moving.

Last edited: Sep 10, 2014
15. Sep 11, 2014

### Staff: Mentor

This is an incredibly classical, and therefore incorrect, point of view. The electron's state is governed by quantum mechanics, which tells us that the electron is not occupying one position, then another. It is therefore meaningless to talk about the electron "moving." It is in a stationary state.

Another way to see it is that the electron is in a superposition of being in different places at the same time.

16. Sep 11, 2014

### Delta²

So you actually saying that particles in quantum mechanics never move??? They teleport from one position to another? And what is the meaning of the momentum/velocity of the particle if they dont move??

17. Sep 11, 2014

### Staff: Mentor

No, far from it. I'm talking specifically about electrons in a bound state in an atom.

Again, you are stuck on the idea of "moving". Teleporting would be the same as moving, but in discrete steps. What I am saying is that the electron is in many places at the same time, not jumping from one place to the next.

The thing is that an electron in an atom also doesn't have a definite momentum, it is also in a superposition of various "fast" and "slow".

I don't want to derail this thread, so I won't go into more details, but it's one of the important conclusion of quantum mechanics. Electrons in an atom do not orbit around the nucleus, they are in diffuse orbitals, diffuse both from the point of view of regelar space and momentum space. It seems strange from the classical/macroscopic point of view, but this is what the theory, which is very well backed by experiments, tells us.

18. Sep 11, 2014

### ChrisVer

An electron confined in some space $\Delta x = \mathcal{O}(1-100 nm)$ will not have definite momentum due to the uncertainty principle... it's momentum will be undefined by $\Delta p = \frac{1}{1-100 nm}$ in natural units.
my score doesn't stand for "minus", but for "to".

You can try to calculate the "classicaly" behaved expectation value of the electron's momentum in Hydrogen atom's ground state. What you'll get will be zero... as someone expects from bound states (look at Dr Claude's post above, and the posts in the link below):

Last edited: Sep 11, 2014
19. Sep 11, 2014

### Staff: Mentor

You should however note that $\langle p^2 \rangle > 0$.

20. Sep 12, 2014

### Delta²

No i strongly disagree, electron is a point particle, and at a given time it occupies a single point in space and it has a definite momentum. It is just that we dont have the technology to measure with infinite degree of accuracy its position or momentum , the current theory says that its impossible to measure with infinite degree both of them, and we also dont have the theory to predict exactly its position or momentum. The best current theory give us is a probability cloud in which the electron lies, but you are going way too far ahead to assume that just because the theory give us a probability cloud, this means that actually (in the physical reality) the electron occupies simultaneously all those points in the theoretical probability cloud.