 Now, remember, neutrons are particles, subatomic particles, also found in the nucleus. So the nucleus contains the protons, which the number of those tells you what element you have, and then it contains neutrons. The number of neutrons in an element doesn't change it. So you can have different forms of, say, carbon that have different numbers of neutrons. If you change the protons, you don't have carbon anymore. But if you change the neutrons, you do. You just are changing the mass of the atom. And I'm going to write this down right now for you. Neutrons of the same element, but with different numbers of neutrons, are called isotopes. Isotopes are crying out loud. Look, I did that for you. I backed it up and wrote the whole word out, isotopes. You can have many different isotopes of each element, and carbon is a great one. It gives us, we actually, you may even know about the isotopes, the carbon isotopes. The most common isotope, let's do that. The most common is the most stable. And I want you to think about that for a second. I don't know, I sort of, atoms are like anything else. Like they, there is a stable state where the number of neutrons, the number of protons, and the number of electrons sort of are energetically, I don't know, I want to say maximized, like efficient. The number is right and the molecule, the atom is stable. The isotope is stable. Some isotopes are less stable. Those are less common because they're not as stable, right? That makes sense. And in fact, the less stable isotopes can actually decay and become the more stable isotope. And that happens over time. So this is, and sometimes there are radioactive particles that are released during this decay process. So less stable isotopes can decay into the more stable isotopes. That works, yes, that that, that intuitively makes sense. Well, in the world, all the atoms have isotopes that are most stable. Some of them have other forms of isotopes that also exist. Carbon is super interesting. Our most stable isotope of carbon is carbon 12. You can kind of get a sense of that. There's a little bit of hint here with this atomic mass number, which is the average mass of all carbon atoms that you could possibly find. So this number gives you a hint. It's a little bit bigger than 12. The most common isotope of carbon is carbon 12. And that just means that it has, of course, six protons and it also has six neutrons. Hence carbon 12. Let's change the number of neutrons to get a different isotope. I'm going to tell you what it is. I'm going to write it down here in a different color. We'll make it orange. Carbon 14 is a different isotope. You tell me how many protons are in carbon 14. How did you know that there were six protons in carbon 14? Because if it didn't have six protons, it wouldn't be carbon anymore. That's cool. It doesn't have to be carbon, but if it is carbon, it's going to have six protons. How many neutrons do you think it has? How many neutrons are in a carbon 14 isotope? Well, if you did some math, six plus eight equals 14, then you correctly discovered that the isotope has two extra neutrons and is therefore called carbon 14. Now, if we were all hanging out in person, I would say to you, has anyone ever heard of carbon 14 before? And I hope someone out there would raise their hand and say, yes, yes, I have. Carbon 14 is not super common, but common enough that it decays at a known rate and it's used to determine the age of really old things like fossils and artifacts and other cool stuff. We can use carbon 14 dating. Have you heard of that? To measure the number of carbon 14 isotopes in a sample of something and compare it to how many carbon 12 isotopes are in there. And the younger it is, the more carbon 14 will be in the sample because it hasn't decayed. Does that make sense? The older it is, the less carbon 14 because it hasn't decayed into carbon 12 yet. There's another application that I want to talk to you about because I think this is really, really cool. And this application has to do with medical imaging. And I want to show you this picture of a glucose molecule. And these are two almost identical glucose molecules. I don't know if you can. Oops, let's go back. So I was just wanting you to see my mouse. I hope you can see it. One of the glucose molecules is normal. And the other one, we added a radioactive fluorine isotope to that glucose molecule. So now you have an isotope of fluorine. We could go look at the periodic chart for fluorine and we could figure out how many neutrons are in this fluorine and how many neutrons are in a normal fluorine. It decays over time and the time it takes for this to decay is really short. If you drink radioactively labeled glucose molecules and then let your body cells eat the glucose, which is what your body cells are going to do, the cells that eat more are going to have more radioactive glucose. And that radioactive fluorine is going to decay and it actually emits light that can be imaged. It's so cool. Now, so cool. Way cool. Yay. Tough application that's used to detect cancer because cancer cells metabolize way more, way faster they eat, way more glucose than a non-cancer cell. And that's one of the ways that we can diagnose whether or not a tumor is concerning. Now, I want to show you a picture of how this can be used, not just for medical purposes, but also for studying brain function. Here's an image of this person ate the radioactive fluorine-marked glucose molecule and then did a job, learned a skill. I don't know what this was if they were playing the piano or what they were doing, but they had their brain imaged while they were doing this task. When they were not practiced, when they hadn't done this thing that they were asked to do, you can see from the imaging what parts of their brain were most active. Those glowing parts were using more glucose than the other parts. And after they practiced, the brain changed. The part of the brain that was active changed. And we could see that change because a different part of the brain, a different part of the brain's cells were super active doing the work after you'd done the practice. Think about something that you have done in your life but it took time that you got good at it. I play volleyball and I played all when I was a kid and played all through high school and a little bit in college. And the skills pretty soon, I actually started playing again. City League for middle-aged ladies, super awesome. I have a blast. It's amazing to me what my body remembers. I can't jump for do-do and my legs won't move. My quickness is garbage. But my body remembers how to do the skills because I practiced and have a different part of my brain that is activated. I also remember learning the skills. I remember what it felt like to not be able to do the skills. And it wasn't that long, you know, I definitely have a visual feeling of what that is like and my brain was functioning differently during that time. Okay, I could talk about this stuff all day long. I'm sure you can tell. I think isotopes are really, really interesting. And again, we're going to mess with them all semester long. Let's do electrons next.