Please forgive any abuse of technical terms in this post. It’s been a long time since my last chemistry class.
The reason that iron is attracted to magnets has to do with the imbalance of the electron shells – at least that’s what I understand from this. When iron combines with oxygen to form rust (ferrous oxide) that substance is not magnetic even though it is iron based because the oxygen atoms match up with the iron atoms in such a way that the electron shells are in balance. Is that right?
So, if it’s all about imbalanced electron shells, one would expect that there would be substances that are made up of none of the ferromagnetic elements but are magnetic anyway, just because when the way the atoms come together to form molecules, the outer electron shell gets left out of balance. Do such things exist?
I don’t know the theory well enough to comment, but yes, such things exist: Heusler alloys, which are ferromagnetic, but made of compositions such as Cu2MnSn.
I remember going to a chemistry lecture where the lecturer said that many elements show magnetism, but it is much less pronounced than the effect in iron, nickel and cobalt.
The lecture was about liquid oxygen. He put a test tube of liquid oxygen on a long pendulum, and was able to show how the tube moved when a magnet got near it. It didn’t move very much, but it did move.
Bakhesh, that’s paramagnetism, not ferromagnetism. The two are similar insofar as both paramagnetic and ferromagnetic materials are attracted to a magnet. The key difference is that a ferromagnetic material will remain at least somewhat magnetized, even after you take the original magnet away.
There’s also diamagnetism, where a substance will (weakly) be repelled by a magnet. All (or nearly all; I’m sure there are some oddball exceptions) substances are magnetic in some way, with most things (including water and most organic materials) being diamagnetic, some things being paramagnetic, and a very few being ferromagnetic. But since ferromagnetism is typically much stronger than the others, it’s the only one you notice.
Paramagnetism, diamagnetism, ferromagnetism; is it fair to say that they are all based on the same physical property, i.e., the outer electron shell being out of balance with the rest?
So it looks like the thing that gives iron its strong magnetism is the 5 to 1 imbalance in an electron shell. So is this one of those exponentially increasing things such that a 2 to 1 imbalance will show a barely perceptible magnetism, 3 to 1 is still pretty much nothing, and you need to get to 5 to 1 before things really start happening? If so are there substances with 6 to 1 or greater imbalances?
Diamagentism and paramagnetism are opposites. Paramagnetism is brought about by unpaired electrons, diamagnetism by paired electrons. Since chemical bonds are pairs of electrons shared by atomic nuclei, virtually every material is diamagnetic. Non-bonding paired electrons (such as those in filled shells) also produce diamagnetism. But, like Chronos said, this effect is very very weak, so we don’t bother to think about it much/at all.
Ehh. I’ll have to try this out. I seem to remember reading (in a very old physics book) that water was slightly diamagnetic and actually would be repelled by a magnetic field.
The demonstration I saw in physics class that impressed me was when the prof showed that a big permanent magnet can’t pick up a piece of copper…but it can sure slow copper down! He took a spinning disk of copper…and when he put the disk betwen the poles of the (large!) horseshoe magnet, the disk slowed to a halt. The prof also took a strip of aluminum and dropped it, so that it fell, freely, between the magnet’s poles. It fell slowly…then, once free of the magnet, fell at a more normal acceleration.
So my question is: this is “ordinary” magnetism, isn’t it?
Trinopus: that’s ‘eddy current damping’ and to do with current/field interaction rather than magnetic properties of materials. When a moving conductor cuts a magnetic field, eddy currents are induced in the conductor, which interact with the field to oppose the movement.
Mangetout: there’s an article about one here. Weak, as you say, and only stable at cryogenic temperatures. A Google search finds a few references to compressed buckyball sheet that’s weakly magnetic (ferro, I assume) at room temperature.
Hrrrrmmm [Marge Simpson noise]. I can’t get it to work even with the big magnet from my Levitron base, and I’m a bit suspicious as to why it should attract anyway (as you say, water is diamagnetic). Maybe this is about electrostatics?
I doubt it’s the magnetism. I have some really high-energy rare earth magnets, and I can’t get the stream to flinch a bit. I’m with raygirvan on the electostatic idea.
Apparently you can get a powerful magnet (one of those neodymium jobs) to push a dimple in the surface of water. I tried the stream thing and got nothing.
