 Okay, let's look at how we write about our chemicals because that is relevant as well. First of all, any element is indicated by the letters on the periodic chart. So for example, the letter H is indicating a hydrogen atom. The letter C is carbon. And we think the letter O is oxygen. These three in particular are probably ones that you want to be familiar with. You want to be aware when a letter is representing an element. I'm going to give you another example of something called ATP. The next thing is adenosine triphosphate. Phosphate? Wow. Adenosine triphosphate is not an atom. It's actually a molecule, but it's not like a molecule of A, which I don't even think that exists. And T, yeah, those don't exist. T exists. It is a phosphorus atom. But this would be an example of a molecule that has its own little name. So you want to be sure that you know, like when are we talking about atoms? When are we talking about molecules? And when are we talking about something that has just its own name and acronym? Oh, and there'll be lots of those. So the letter comes from the periodic chart. If in doubt, ask. You don't have to memorize most of these things, but there are going to be some that you're going to memorize. If you put atoms together, then you get a molecule. I'm going to give you an example of a molecule. H2O is an example of a molecule. Tell me, talk to me, dog pounds. This is a molecule of what? You will know this one. It's a molecule of water. And tell me what's it made out of? Well, do you agree with this? It's made of one hydrogen atom. How many hydrogen atoms do you think? Two hydrogen atoms connected to what? One oxygen atom. In fact, that I just drew right there is a picture of a water molecule. What do you think this little line represents? It represents a chemical bond. A chemical bond, which is how we ended up with a molecule in the first place. That chemical, what is it? What is a chemical bond? I know, don't you love it? Those are shared electrons. And we'll learn about water and we'll see, like what kind of bond do you think it's a covalent bond? Do you think it's an ionic bond? Is it a polar covalent bond? We're actually going to look at exactly what kind of bond this is. So, if we wanted to show two water molecules, here's one water molecule. If I wanted to show you two water molecules, if I'm going to draw it this way, okay, do you agree that now I have two water molecules? And you tell me, do I write it like this now? How many hydrogens? Two, three, four. H, four. How many oxygens? O, two. Is that equal to two water molecules? I'm going to put a big old question mark because I want you to answer that question. Do you think that that is two water molecules? No, please. No, no, no. Do not be confused. You stopped watching the lecture right before that and you think that this is two water molecules. I'm not going to feel sorry for you when I take points away from you for saying something like that on a quiz or an exam. No, that you cannot. This means, I'm going to draw you a picture of this. I don't even know if this thing exists. That's actually H, H, H. I'm just going to make this up because you know I really don't think this thing exists. So O, O, and then we're going to form chemical bonds between these things. Okay, we'll put one there, we'll put one there, we'll put one here and here and here. Why not? Totally doesn't exist. However, that's what I just drew. There are all sorts of rules that you'll learn in chemistry for how to put atoms together. You could totally figure out what we would have to do in order to make that possible. I'm pretty sure that, well, I'm not even going to think about it, but if we want to say we have two water molecules, that's where we put in something called a coefficient. This is a subscript. The subscript tells me how many atoms are in the molecule. The coefficient tells me how many molecules we have. So in this case, we have two molecules of water. Hmm, I think we're good. Now, I'm going to show you a chemical equation, a chemical reaction taking place, and I'm going to show you one that involves water. So watch. We can actually combine. This is a true story, my friends. A hydrogen ion. And how did you know that I made this into an ion? A hydroxide ion. Look, let's just make a notation of that too. This is the charge of the atom. So we know that we have a hydrogen atom, which means it has one proton, and we know that it doesn't have an electron at all. We stole it. Somebody stole it. And now it has a positive charge. Meanwhile, there's this other molecule called a hydroxide molecule, and it has a negative charge. So this whole thing, this whole molecule, has a negative charge because it has one extra electron. But guess what? What's going to happen if we combine a hydrogen and a hydroxide? Go ahead and take a wild guess. Dogs of a feather. We're going to get a water molecule. Two hydrogens and one oxygen combine to form water. And this little arrow right here, that tells you the direction of the reaction. So you can have this reaction proceed in the other direction, and it actually does. And an accurate depiction of this little system has arrows going both directions because the hydrogens and hydroxides combine to form water and the water splits to form hydrogens and hydroxides. Uh-oh, we're getting visited. Hello. I'm recording a lecture. That's okay, you're totally good. See ya. I'm not stopping, that's okay. The direction, we can go either way, that's awesome. What else do I have to tell you? I think that's it that I'm going to tell you. I think that's it that I was supposed to tell you. I should have just stopped it right before the janitor came in. That's great. All right, y'all. You now know all the chemical notation that you need to know, right? I hope so. Okay, I'll see you later. Bye.