Have you ever seen something like this?
I’m going to venture a wild guess and say you haven’t, since scientists have only recently been able to take this kind of image. I learned about it in my biology class this semester, and the professor said that it was a landmark achievement.
You’re looking at an atom.
Yes, that’s right. You’re looking at a single, microscopic building block of matter.
Let me give you an idea of just how small this is. Millions of the smallest atom in the universe can fit lined across the diameter of a single pinhead.
But I’ll ask you another question. If I showed you an image like the one below, would you immediately think, “atom”?
Chances are you’d think something science-related, and if you’ve heard of atoms before, you’ll probably recognize this as an atom.
They look a bit different in real life, don’t they?
So…here’s a third question. What’s going on with that image, anyway? Is it just really fuzzy, or can we actually not see individual electrons? I mean, it looks like a fuzzball with a nucleus inside, not a nucleus surrounded by orbiting electrons.
Alright, I’ll let you in on the greatest secret of quantum mechanics. It’s true. Electrons don’t act like matter. They do a weird sort of disappearing act. And we can never know both where they are and how they’re moving at the same time.
Whether electrons are actually a “particle” is debatable. That’s a debate I’m not part of—I leave that to the quantum mechanics experts. What I know is that there’s a better way to think about atoms than the traditional model with protons, neutrons, and electrons.
Meet the “cloud” model.
Electrons don’t have precise orbits around the nucleus of their atom, at least not that we can see. There’s no experiment we’ve done that can track the position and motion of an electron at the same time. It’s like they don’t properly exist.
So we refer to the electron “cloud.” It’s a region of space surrounding the nucleus that tells you where an electron might be at any one time.
But here’s the bit that’s really going to blow your mind away…
…Everything we know about atoms, and thus, everything we know about what the universe is made of, boils down to where electrons might be.
Now, add enough atoms together, watch enough chemical reactions, and the balance of probability “balances” out. It gets more certain the more electrons are involved, of course because if you have enough electrons to do stuff, every possibility will happen.
If we’re talking about just one electron, though, it’s impossible to know both where it is and where it will be. It all boils down to a chance. That’s why we can’t see electrons in images of atoms. They could be anywhere in the cloud. But they are somewhere.
Anyway, that’s enough on the sheer wackiness of electrons. How about some talk on how they work? Because this part is key to astronomy.
This diagram looks a bit mathy, but the important part is something you already know. Tell me, what happens when you try to touch two ends of a magnet together that have the same charge?
Like charges repel. Unlike charges attract. It’s a law of nature that we’re all familiar with. At least, you’ve seen this in action if you have magnets on your refrigerator. Ever wonder why they “stick” without being sticky? Because that’s the power of attraction.
Um…no, not that kind of attraction.
I’m talking about the attraction of positive and negative charges. (Why they’re called that is beyond me—maybe just because they’re opposites?) That’s what holds electrons to the nucleus. Positive protons in the nucleus attract negative electrons.
The law of positive-attracts-negative even has a name in quantum mechanics. It’s called the Coulomb force.
So, it takes a force to hold electrons in an atom. It’s going to take a slightly stronger force to break them away. That’s called the electron’s binding energy. Binding energy holds an electron to its atom, and you need at least the binding energy to break it away.
Basically, “Coulomb” is the name of the force, but the binding energy tells you how much force there is.
Now, time for another question. Try holding an object tightly to your chest. Ask someone to try and grab it from you. Now have them try again, but this time hold it far from you with just one hand. On which try did they manage to grab it from you?
You probably know the answer without actually trying it. It’ll be easier for your friend to rip the object away if you’re holding it away from you to begin with.
It’s the same story with electrons. We may have trouble knowing where exactly they are in an atom, but we know that if they’re towards the edge, they have less binding energy and get ripped away more easily.
We have trouble knowing where exactly electrons are, but we have no trouble at all knowing where they can be. That depends on permitted orbits.
Remember the electron cloud? Well, it’s not a single, boring, monotonous cloud.
It’s more like a series of rings, nested within each other. We have labels for them, as you can see here, but that’s not important for this post. Right now, all I hope for you to take away from this is that electrons will always be found within these specific rings.
They’re like steps in a staircase—you can stand on step one or two, but not on step one-and-one-quarter. It doesn’t exist, and it certainly doesn’t exist in an atom.
In an atom, an electron can be found in any one of the orbitals, or permitted orbits. But it can’t ever be between them. That certainly narrows the possibilities down.
Get this, though. Even hydrogen, which has one single electron orbiting one single proton, has multiple orbitals. Every atom has a bunch of them. You’ll find out why this is in my next post.
Here’s the catch, though. The orbitals don’t look the same for every atom.
So how can we hope to find a single electron?
Well…it helps that we know what makes orbitals take on different shapes. It depends mostly on the charge of the nucleus, so on how many protons there are—which tells you what kind of atom it is.
And lucky for us, neutrons don’t make much of a difference. The neutron count can be a little different from the proton count depending on the atom’s isotope, but since neutrons have no charge, they don’t affect the orbital shape.
That means that every one of the same atom, regardless of its isotope, has the same electron cloud.
Because ions—atoms that have lost or gained electrons, and thus have a positive or negative charge—have a charge, that affects the shape of the orbitals. Fortunately, we have ways to predict that.
Now that we’re more familiar with atoms and how they work, we can finally take a dive into how they interact with light. And that’s coming up in my next post!