I thought spin did mean rotation, although I also recall everytime I read about it there would be some equivocating remark about how spin wasn’t “really” spin, but I didn’t think it wasn’t really spin to the extreme of the quarks not really being colored.
I also know that there are no books that I ever come across that have any pictures in them anymore of particles or atoms. On the other hand, strangely, quantum theory is said to involve lots of very strange geometric shapes of mathematics!
I heard too that spin does have something to do with which way the particle goes when it bounces off something else. It goes the way it would go if it was a ball actually rotating (vide billiards and spun baseballs, et. al., eg.) But I’m not sure.
Signed, Utterly Disheartened By an Atomic World Without
Pictures, UDBAWWP
Grimpixie, I’m afraid the classical radius of an electron is just a size scale and not a hard number. As far as any experiment that I am aware of has been able to determine, an electron is a point particle. That is, we can’t probe it closely enough to be able to observe structure do it, unlike with, say, a proton. But when you get that far down, size is a very very nebulous concept and all we can really talk about is size scales. For instance, the size of a hydrogen atom is on the order of a Bohr radius, but it’s not like you have a little ball that’s 1 Bohr across. A proton is on about 10[sup]-15[/sup] m across (IIRC), but again, no hard number should be given.
Contrary to grimpixie’s post, this is actually a pretty sensible question, though my answer is going to boil down to “it depends.”
First of all, grimpixie’s right that elementary particles like electrons and Higgs (I’ll come back to composite ones like Xi at the end) are far smaller than visible wavelengths; as g8rguy notes, they’re point particles as far as is known. And it’s also certainly true that usually this means that an object won’t noticably interact with light of this wavelength. However, this is because of issues like wave diffraction, which is a classical way of thinking about light and everyday objects. Once you’re thinking about photons and charged point particles, things can get a bit different. Not only can electrons interact with light, this is pretty much what electromagnetism is.
The main relevant scattering process of photons off electrons is called the Compton effect. It was first observed with X-rays, which in the grand scheme of things are not so unlike visible light. Calculating what frequencies are scattered at what angle is a relatively (certainly compared to what comes next) simple exercise in undergraduate textbooks. That however doesn’t tell you much about the probability of a photon of a particular wavelength scattering. That’s a relatively simple exercise in quantum field theory at graduate level. Much to the annoyance of people building particle colliders, it’s a very typical result that collision cross sections fall off with higher energies and this is one such case. Contrary to grimpixie’s classical reasoning, a very short wavelength photon is less likely to be scattered than one of longer wavelength. What the actual results are for optical photons, I don’t know offhand. A detailed answer would depend on knowing the illumination conditions. But it’s all calculable.
At least one picture of a single electron does exist. It was published a few years ago by a team who’d used advanced trapping technology to isolate and hold a single one in some configuration of electic and magnetic fields. I think they then shone a laser on it and simply took a photograph. And this electron looked like … big drum roll … a pale blue dot. Pleasingly exactly like what they’re always pictured as, alongside red protons etc. No doubt this was largely a consequence of the laser used. Sorry, no cite.
Higgs particles (at least in the minimal Standard Model) are electrically neutral. They don’t interact with photons directly. So basically you wouldn’t see them.
Composite particles like a Xi or protons are much harder to deal with. For a start they can absorb a photon completely.
Wow. you’ve been really helpful, bonzer. And everybody else too. I certainly don’t understand any more than I did when I asked the question, but now I see very much more clearly why I don’t understand. 
Fair comments bonzer… this is one of the reasons I chose Chemistry over Physics!! 
IIRC it is the atoms of the diode-material that interact with the light and absorb the energy which results in the promotion of the electron to an excited energy state. This is an unstable situation and when the electron tumbles back to “ground zero” the energy of the atom is reduced and it compensates by emiting this energy in the form of a photon of (often visible) light.
So it is the atom rather than the electron that absorbs the light, and atoms are a little bit bigger than electrons.
Gp
grimpizie, “normal” atoms are electrically neutral, but are comprised of particles that “feel” the electromagnetic force.
Electrons feel the electromagnetic force.
The electromagnetic force is mediated by a photon.
Thus, electrons interact with photons.
(light emitting)Diodes work by mixing atoms which have different valence configurations, resulting in excess electrons or excess holes. The configuration between the anode and the cathode is such that when an electron moves across the potential it must emit visible light to do so.
Frankly, much of this sort of this stuff is deciding more clearly what one doesn’t understand. Nobody understands all of it. But you asked a damn good question. Put it this way. The question you asked could have been asked anytime from about roughly 1920 onwards (maybe even 1900). By then they were pretty sure they knew about electrons and they had fairly crude ideas about protons. But they did know they were opposite in charge. They didn’t know why. Even the partial answer I outlined didn’t become clear until the late 70s. Something that keeps physicists arguing for over half a century and beyond is a very good question.
Confessions, confessions … Now that you’ve admitted to being a chemist, grimpixie, it should be said that your reasoning is pretty much applicable at the atomic level. But not below.
Non-physicists and non-chemists should avert their eyes from the above border dispute.
It just occurred to me that maybe i should reccomend the book ‘The Elegant Universe’ to you wevets. It tries to explain lots of stuff using string theory. Of course,it doesn’t give any 100% clarifications(is that even a word?) or answers,but you would understand alot of this stuff better. Plus,you don’t have to be a genius to read the book.
There’s no real upper limit on the size of a particle. You could, if you liked, call the entire Earth a particle. It’s a very complicated particle, to be sure, and made up of gazillions of smaller particles, but then, protons are made up of smaller particles, too, and nobody has any qualms about calling a proton a particle. If you want a simple particle, then you can consider a black hole a particle. Black holes have only four “internal” properties, which is less than you have in a typical atom, so they’re quite simple, and they’re not made up of atoms, so they could be considered "sub"atomic.