# Why isn't aluminum magnetic? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [April 4, 2007, 7:17pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751 "2007-04-04T19:17:19Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Jelymag](https://avatars.discourse-cdn.com/v4/letter/j/d2c977/32.png) [@Jelymag](https://boards.straightdope.com/u/Jelymag)\ **Post date:** [April 4, 2007, 7:17pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/1 "2007-04-04T19:17:19Z")
I’ve never heard reference to the _M_ shell. Is that n=3? I didn’t realize they also went by letters? [Here](http://www.straightdope.com/classics/a3_339.html) is the article. ---
**Author:** ![Dr.Lao](https://avatars.discourse-cdn.com/v4/letter/d/2bfe46/32.png) [@Dr.Lao](https://boards.straightdope.com/u/Dr.Lao)\ **Post date:** [April 4, 2007, 9:04pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/2 "2007-04-04T21:04:58Z")
[QUOTE=Jelymag] I’ve never heard reference to the _M_ shell. Is that n=3? [/quote] Yes. > [@](#): > > I didn’t realize they also went by letters? Neither did I. > **[Electron shell](https://en.wikipedia.org/wiki/Electron_shell)** > > In chemistry and atomic physics, an electron shell may be thought of as an orbit that electrons follow around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" (also called the "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on further and further from the nucleus. The shells correspond to the principal quantum numbers (n = 1, 2, 3, 4 ...) or are labeled alphabetically with the letters used in X-ray notation (K, L, M, ...... It seems like the letter identifier predates the quantum theory of the atom and related to spectroscopic absorption lines. It was only later that these shells were correlated to the quantum n numbers. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [April 4, 2007, 9:17pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/3 "2007-04-04T21:17:22Z")
As I understand String Theory, which is to say not very well at all, the Stringies say electrons don’t actually spin. How do Stringies explain why magnets won’t stick to aluminum? Maybe I shouldn’t even ask. I know my head is going to spin, and maybe not in the same direction. :smack: :eek: ---
**Author:** ![Dr.Lao](https://avatars.discourse-cdn.com/v4/letter/d/2bfe46/32.png) [@Dr.Lao](https://boards.straightdope.com/u/Dr.Lao)\ **Post date:** [April 4, 2007, 9:24pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/4 "2007-04-04T21:24:16Z")
Spin refers to a quantum property, not literal spin. Since electrons are point masses in the standard model, they can’t literally spin either. So, it doesn’t really matter whether you are talking standard model or string theory, neither allows for literal spin, but both must allow for the quantum property known as spin to exist since it has been verified to exist experimentally. ---
**Author:** ![Jelymag](https://avatars.discourse-cdn.com/v4/letter/j/d2c977/32.png) [@Jelymag](https://boards.straightdope.com/u/Jelymag)\ **Post date:** [April 5, 2007, 4:05pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/5 "2007-04-05T16:05:55Z")
[QUOTE=AskNott] As I understand String Theory, which is to say not very well at all, the Stringies say electrons don’t actually spin. How do Stringies explain why magnets won’t stick to aluminum? [/QUOTE] My knowledge about String Theory is less than not very well, so I have no idea how they might explain magnetism. [QUOTE=Dr. Lao] Neither did I. > **[Electron shell](https://en.wikipedia.org/wiki/Electron_shell)** > > In chemistry and atomic physics, an electron shell may be thought of as an orbit that electrons follow around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" (also called the "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on further and further from the nucleus. The shells correspond to the principal quantum numbers (n = 1, 2, 3, 4 ...) or are labeled alphabetically with the letters used in X-ray notation (K, L, M, ...... It seems like the letter identifier predates the quantum theory of the atom and related to spectroscopic absorption lines. It was only later that these shells were correlated to the quantum n numbers. [/QUOTE] Thanks, that’s interesting. I read the wiki page; I also didn’t know s, p, d, and f ever stood for anything, let alone “sharp,” “principal,” “diffuse,” and “fundamental.” Explain more to me about “spin” doesn’t mean _spin_ please. I get that an electron is not literally spinning in the sense of rotation. I guess I never thought of it, but what property are we actually talking about if we’re not talking about spinning? And if it isn’t spinning, what is the point of refering to electrons with an opposite spin? ---
**Author:** ![tim314](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tim314/32/3468_2.png) [@tim314](https://boards.straightdope.com/u/tim314)\ **Post date:** [April 5, 2007, 5:02pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/6 "2007-04-05T17:02:02Z")
There’s a lot that can be said about spin, but here’s the jist: When electric charges rotate, you get a magnetic moment (basically, they act like a little magnet.) So for instance a loop of wire with an electric current flowing through it acts like a magnet. (Electric current is just moving charges, and in this case the charges are moving in a circle around the center of the loop.) If you’ve ever played with an electromagnet, you’ve seen this effect. Electrons have a charge of course, but somewhat surprisingly they also have a magnetic moment. You might think that’s because the electrons are moving in circles around the nucleus of the atom. And that does contribute sometimes, but there are some states of the atom where the electrons spend as much time circling one way as the other way. In that case, you’d expect that the effect of the electrons motion would cancel out, and leave you with no magnetic moment. But in fact you _still_ get a magnetic moment. (In fact, you get a magnetic moment even when the electons aren’t part of an atom.) That suggests that the electrons themselves are spinning, in addition to revolving around the nucleus. (\*) However, electrons are so tiny that if they really were a ball of spinning charge, then the surface of the ball would have to be moving faster than light to produce that big a magnetic moment. That’s impossible, so clearly the electron isn’t _really_ a spinning ball, it just _acts_ like it’s spinning. (And it’s not just that it has a magnetic moment, it also acts like it has an angular momentum – i.e., the usual sort of rule for conservation of momentum applies. But I thought the magnetic moment was the simplest example of what we mean when we say an electron “acts like it’s spinning.”) (\*) Note: Quantum mechanics tells us that the electron doesn’t have a fixed position (it’s more like a spread out cloud), so this talk of electron’s “moving in circles” is just an analogy to what’s really happening. ---
**Author:** ![JustAnotherGeek](https://avatars.discourse-cdn.com/v4/letter/j/58f4c7/32.png) [@JustAnotherGeek](https://boards.straightdope.com/u/JustAnotherGeek)\ **Post date:** [April 5, 2007, 5:06pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/7 "2007-04-05T17:06:28Z")
[QUOTE=Jelymag] Explain more to me about “spin” doesn’t mean _spin_ please. I get that an electron is not literally spinning in the sense of rotation. I guess I never thought of it, but what property are we actually talking about if we’re not talking about spinning? And if it isn’t spinning, what is the point of refering to electrons with an opposite spin? [/QUOTE] “Spin” represents a sort of symmetry. Imagine a square. If you rotate it 1/4 of the way around (in the page), it looks like the original square, no? If it’s a rectangle, instead, you have to rotate it 180 degrees. In these two cases, they have a spin of 4 and 2, respectively. If you’re quick on your feet, you’ll notice that the electron’s spin of 1/2 will mean that it needs to be rotated _720_ degrees in order to be symmetrical again. What that means I have no idea, though… -Geek (Who’s gotta run…) ---
**Author:** ![Corner\_Case](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/corner_case/32/234_2.png) [@Corner\_Case](https://boards.straightdope.com/u/Corner_Case)\ **Post date:** [April 5, 2007, 5:41pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/8 "2007-04-05T17:41:45Z")
I like **tim314** ’s response. It was hat I was looking for when I asked a similar question in [this](http://boards.straightdope.com/sdmb/showthread.php?t=395263) thread and which referenced [this](http://boards.straightdope.com/sdmb/showthread.php?t=110772) thread. As to spin being 1/2 - the analogy to rotating 720 degrees is interesting. It suggests to me that there is another coupled spin 2 “rotation” taking place. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 5, 2007, 5:47pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/9 "2007-04-05T17:47:24Z")
Spin is a kind of angular momentum. At the quantum scale, there are two kinds of angular momentum: Orbital angular momentum and spin. Orbital angular momentum is familiar enough: It’s the angular momentum one thing has due to moving around another thing. You have to be careful how you define “moving around” in quantum mechanics, but it’s basically the familiar angular momentum. All classical angular momentum is of this type: Even if you have something like, say, a spinning baseball, its angular momentum is due to all the pieces of the baseball moving around the center of the ball. But orbital angular momentum, by itself, isn’t conserved. However, whenever the total orbital angular momentum of a system changes, we observe that there’s also another property, associated with individual particles, not pairs of them, that also changes. When you add the orbital angular momentum together with this other property, you find that that total _is_ conserved. So we conclude that that other property is also a kind of angular momentum, and since it’s associated with individual particles, rather than pairs of them, we call it “spin”. ---
**Author:** ![tim314](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tim314/32/3468_2.png) [@tim314](https://boards.straightdope.com/u/tim314)\ **Post date:** [April 5, 2007, 6:07pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/10 "2007-04-05T18:07:30Z")
[QUOTE=JustAnotherGeek] “Spin” represents a sort of symmetry. Imagine a square. If you rotate it 1/4 of the way around (in the page), it looks like the original square, no? If it’s a rectangle, instead, you have to rotate it 180 degrees. In these two cases, they have a spin of 4 and 2, respectively. If you’re quick on your feet, you’ll notice that the electron’s spin of 1/2 will mean that it needs to be rotated _720_ degrees in order to be symmetrical again. What that means I have no idea, though… -Geek (Who’s gotta run…) [/QUOTE] Here I’d posted a nice simple explanation, and you just had to go and math everything up 😉 To people who are wondering what this business about rotational symmetry has to do with the stuff I said above, let me try to explain: When people talk about a particle having spin n (where n is 1/2, or 1, or 3/2 or whatever) that means its angular momentum is n times some fundamental constant. However, the particle’s spin also determines how it transforms under rotations. For ordinary things, if you rotate them by 360 degrees you get the same thing you started with. (As **JustAnotherGeek** pointed out, sometimes rotating by a smaller angle will also do, but in any case 360 degrees always works). However, if you rotate the state of your electron by 360 degrees you _don’t_ get what you started with – you get _negative one_ times what you started with. Rotating another 360 degrees produces another factor of -1, giving you back the original state. You might find it troubling that an electron’s state isn’t the same after you’ve rotated by 360 degrees. But the good news is that any physical quantity you can actually measure will depend on products of an even number of these states, so the -1’s end up cancelling out. (Note that -1 raised to an even power is just 1). So rotating your entire experiment by 360 degrees should leave the results unchanged, as we’d expect. As for _why_ a particle’s rotational symmetry is related to its intrinsic angular momentum, I don’t really have time right now to go into it, but maybe someone else will take a stab at explaining it. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [April 5, 2007, 7:43pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/11 "2007-04-05T19:43:41Z")
[QUOTE=Dr. Lao] Spin refers to a quantum property, not literal spin. Since electrons are point masses in the standard model, they can’t literally spin either. So, it doesn’t really matter whether you are talking standard model or string theory, neither allows for literal spin, but both must allow for the quantum property known as spin to exist since it has been verified to exist experimentally. [/QUOTE] Next you’re going to say that quarks don’t really have color or flavor, either. What strangeness will you charm us with next? Stranger ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [April 5, 2007, 9:31pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/12 "2007-04-05T21:31:10Z")
Oy! This is some deep, serious material. My prediction was correct; my nead is spinning. It’s not spinning literally, of course, but only theoretically, in a quantum sense. I thank you all for exercising my brain in this way. I have learned a lot, or at least I theoretically did. It is strangely satisfying to find it revealed that I am more ignorant than I thought I was. I understand a little more about magnetism and the way electrons work, but there are whole warehouses of knowledge about subatomic particles that are mysterious to me. I am comfortable with that, and somehow pleased to be aware of it. I keep thinking of the old work song: “You gotta jump down, turn around, Now you’re magnetic. Jump down, turn around, Now you’re minus one.” I’m going to keep an eye on this thread. I have a feeling I missed some things the first time through. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [April 6, 2007, 8:53pm UTC](https://boards.straightdope.com/t/why-isnt-aluminum-magnetic/398751/13 "2007-04-06T20:53:33Z")
Do not feel bad. For a synthetic chemist, I like to think I have a fairly good understanding of quantum chemistry. This stuff still makes my head spin.