Does an electron actually spin around its axis?

[2sin54]

I am a High School student and I was told that magnetic field appears whenever you align the electrons around the atoms (when they spin in the same direction around their axes). Is this true or do schools actually mislead people?

 

[Isp]

Hi gytax!

To answer your question: no, it does not.

When 'spin' was first suggested by George Uhlenbeck and Samuel Goudsmit in 1925, the name was chosen because, as I am sure you've learned, moving charges produce magnetic fields. When orbitals and energy levels of atoms (such as hydrogen and helium) were being studied, scientists observed what has become known as the Zeeman effect. There was a splitting of spectral lines occurring whenever an external magnetic field was applied on the atom. Moreover, more splitting occurred than expected, which led Uhlenbeck and Goudsmit to suggest that there is another quantum number which is responsible for hyperfine splitting to occur. They asserted that electrons in the orbitals (and ultimately other subatomic particles) have an intrinsic magnetic moment to them. It was well understood by then that current, or moving charges, induce a magnetic field. They ascertained that these electrons must be in some sort of motion, so they gave it a cute little name to convey the concept.

However, we know that an electron cannot be spinning on its axis because the velocity at which it would have to be spinning to produce the magnitude of the magnetic moment measured would have to be faster than the speed of light!

Subatomic particles are strange indeed, and there isn't a clear model for visualizing what spin actually looks like.

Schools do not mislead students. They teach students. A big part of physics is the idea of models. We try to come up with analogies or mathematical formulas to describe behavior. This is why the word 'spin' works fairly well. It trains you to associate the motion of a charge with magnetism.

When you get down to it, an electron isn't even a solid, negatively charged little ball, like most people visualize it to be. However, the picture helps in our learning process.

 

[2sin54]

Thank you for your reply. I guess it will be covered more deeply at the University.

 

[jtbell]

Another reason why "spin" isn't a completely bonkers term for this is that we can verify experimentally that electrons have "intrinsic angular momentum" that contributes to the total angular momentum of an object. See the Einstein-deHaas effect. It's rather similar to the classroom demonstration in which a person sits on a stationary turntable while holding a spinning bicycle wheel. When he flips the wheel over, he and the turntable start to spin in the opposite direction to keep the total angular momentum constant. In the Einstein-deHaas effect, we flip the electron spins in a magnetized object, and the object as a whole starts to rotate.

But we can't associate the electron spin with an angular velocity of a little spinning ball-like electron or something like that. It's simply an intrinsic property of the particle, like mass and charge.