Electrons

[Globex]

I know that electrons form "clouds" around atoms since its impossible to predict exactly where they will be found because of the uncertainty principle (which I don't really understand) but do these clouds represent the electrons themselves or only the movement of the electrons?

When an electron is not around an atom, does it still form a cloud?

When I imagine a stream of electrons flowing through a material, should I imaging a stream of electron clouds moving like a giant swarm of mosquitoes?

How about when electrons absorb energy and release energy? Should I imagine the electron cloud suddenly expanding and then contracting?

When electrons flow through a material, do they go around the nuclei, through the electron shells of the atoms, or do they temporarily become part of the atom and then transfer to an adjacent atom, temporarily becoming a part of it and so on?

 

[Perfection]

I know that electrons form "clouds" around atoms since its impossible to predict exactly where they will be found because of the uncertainty principle (which I don't really understand) but do these clouds represent the electrons themselves or only the movement of the electrons?

The electrons themselves. Electrons are best described by something called a wavefunction, which is basicly a probability density function or a cloud thing. Note that these "clouds" aren't always sphere's or something but take complex shapes. Here's some examples:

When an electron is not around an atom, does it still form a cloud?

Yes

When I imagine a stream of electrons flowing through a material, should I imaging a stream of electron clouds moving like a giant swarm of mosquitoes?

No (I'll come back to this).

How about when electrons absorb energy and release energy? Should I imagine the electron cloud suddenly expanding and then contracting?

Well higher energy wavefunctions do tend to be physically larger, but they're different shapes too, and sometimes the electron escapes the material.

When electrons flow through a material, do they go around the nuclei, through the electron shells of the atoms, or do they temporarily become part of the atom and then transfer to an adjacent atom, temporarily becoming a part of it and so on?

In a good conductor many electrons are delocalized (and these are the ones that conduct), their clouds all sort of merge together to form one huge electron sea throughout the material. When you induce a voltage across the material, it's not an orderly process where each cloud moves over, they continue to drift around chaotically, only that there's now a slight tendency to move more in one direction.

 

[Padma]

Disclaimer: It has been decades since I took Physical Chemistry....

If you think of the electron as a particle, the "cloud" represents where that particle probably is, relative to the nucleus of the atom. As you might deduce from Perf's excellent pictures, these clouds are arranged in "shells" around the atom. The first shell can hold two electrons, which tend to stay on "opposite sides" of the atom. The second shell can hold up to 8, divided between two subshells (2 and 6). The number each shell can hold grows larger, the further from the nucleus it is.

If you apply energy to an electron, you can 'excite' it, causing it to make a quantom leap to the next outermost shell. So, in essence, the "cloud" grows "bigger". Of course, this leaves a "hole" where the electron came from, and is unstable, so the electron will sooner or later release the excess energy, and "fall" back to where it belongs.

In a good conductor (e.g., most metals), the electrons in the outermost shell of the component atoms are only barely "held" by any specific atoms. They are more like a "sea" of electrons, all being shared by all the atoms. When you apply a voltage (essentially adding electrons to one side of the "sea"), they will tend to flow toward the other side. (They are like charges, and so repulse each other.)

 

[Globex]

Thanks, I think I understand electrons a bit better now but a few things still confuse me.

For instance, I don't really understand electron spin. The only thing that I've learned about spin is from A Brief History of Time when Hawking compares spin to playing cards and how many times they appear to look the same if you rotate them 360 degrees. But when I watched this video: http://www.youtube.com/watch?v=WxitGR-9qGA the professor talked about spin directions. I thought that spin in the quantum sense didn't involve actual "spinning" so what does it mean when an electron has a clockwise or a counterclockwise spin?

Also, the professor in the video talks about resistance at around 28:30 where he uses this board with metal pegs and marbles to demonstrate resistance. I know he probably uses marbles to represent electrons since the cloud definition may be harder to grasp but I can't understand how electrical resistance works if you think about the electrons in the cloud sense. What causes electrical resistance and how should I visualize electrical resistance?

 

[Souron]

Also, the professor in the video talks about resistance at around 28:30 where he uses this board with metal pegs and marbles to demonstrate resistance. I know he probably uses marbles to represent electrons since the cloud definition may be harder to grasp but I can't understand how electrical resistance works if you think about the electrons in the cloud sense. What causes electrical resistance and how should I visualize electrical resistance?

Electrons repel each other. They don't physically bump into each other, but as an electron gets closer to another electron, it gets pushed away. This way, if there is a lot of repulsive forces, electrons will progress more slowly, which means that charge moves more slowly, which means less current.

 

[Millman]

That's a nice picture. Reminds you of snowflakes. If electrons are unique then it shows life wants to be complex and different. It looks like it doesn't want to be bored. (DS9 Reference here).

 

[uppi]

That's a nice picture. Reminds you of snowflakes. If electrons are unique then it shows life wants to be complex and different. It looks like it doesn't want to be bored. (DS9 Reference here).

electrons are certainly not "unique". The image is a display of spherical harmonics and it's the same for every electron.