Understanding Electron “Clouds”

Most people have seen what’s called the Bohr model of the atom (’cause it was described by Niels Bohr) — it’s the nucleus with some electrons in orbit around it. (That’s an example on the right.)

Anyway, that model is wrong. It has been since the early 1900s. Well, it’s been wrong since the Big Bang, but we’ve known it was wrong since the 1900s.

A more accurate model would show the electrons as a ‘cloud’ around the nucleus. That’s because, in part, of Heisenberg’s Uncertainty Principle which says that we can never know both where an electron is and where it’s going. So physicists think of a ‘cloud of probability’ — an area in which the electron is in all places at all times.

Huh? In other words, until that electron interacts with something — another atom’s electrons, or a human tester — it’s everywhere in that space. As soon as we observe it, it exists in a single place. But when we’re not looking, it’s everywhere.

That’s a pretty cool concept, but a tough one to grasp. As I was lying in bed I realized a good analogy: a fan.

Imagine a desk fan whirling away. You can’t see the blades because they’re moving too fast. But the moment you stick your fingers (or, preferably, the fingers of someone you don’t like) into it, you know precisely where they are.

Crudely, in terms of quantum physics you’ve “collapsed the wave function” — you’ve turned that ‘cloud’ of fan blades into to blade in a specific location: your finger.

Electrons work sort of the same way. Like the spinning blades, they’re everywhere at once and they can interact with anything in their area. But the moment they interact, they’re in a specific location.

I just thought it was a useful analogy is all.