 So, here we're going to be going over this reaction, sodium plus chlorine, sodium solid plus chlorine gas going to sodium chloride. Okay, this is a chemical change. Why is that? Because on the left side of the reaction or on the reactant side, we have two different types of, well, in this case, particles. Okay, I would say normally types of compounds or molecules, but this is neither a compound or a molecule and this is not a compound, okay? This is a molecule and this is an atom. So, you can collectively say particles, okay? Well anyways, if we look, the molecular formula or the atomic formula of these particles is different than what's on the right side, which is the product side. In fact, the formula for this particle is Na and that's it, okay? The formula for this particle is Cl2. Let's draw that out, okay? Cl2 has, remember, this is kind of what we were talking about on Wednesday and you were asking why do we put the two here, right? It's because we put these two as a subscript here because these two Cls have an actual bond between them, they're stuck together. They're like holding hands, okay? So they act as a unit as opposed to like the sodium atom on the other side which acts as an individual, okay? So in other words, if we wanted to, this is what the sodium atom looks like, okay? And this is what Cl2 looks like, okay? So it's actually stuck together acting as a unit, right? So this sodium atom, this Cl2, it's a molecule with a bond in between those two atoms. Does that make sense? Okay. Okay, so the difference between that and, well, let's balance the equation now, okay? So if we look on this side, we've got, we've got to write down the types of atoms we have, Na and Cl and we look on this side and we have Na and Cl, so that's cool because if we didn't, we would not, definitely not have a balanced equation, okay? So now we're going to go, want to ask ourselves how many of each one of these do we have? On this side, we've got one Na and two Cls, okay? And on this side, what do we have? One Na and one Cl, okay? So in order to get the same amount of Cls on both sides, since this thing is a unit, I can't just stick something else onto it, right? I can't say I want four arms, you know? So I'll take two disembodied arms and put them on a person to make them have four arms. I can't do that. If I wanted four arms, I have to have two people, okay? So that's what you want to think about, okay? So these things are stuck together, okay? You can't just add another chlorine to it, okay? So you've got to put a whole another thing there. So you've got to, in order to do that, you've got to put a two here, okay? So when you put that two there, you're no longer saying they're connected together. Now you're saying I've got one NaCl here and one NaCl here, like that, okay? Does that make sense? This is not really the proper way to show this type of bond, but for right now, it doesn't matter, okay? I just want you to understand the concept. No, it's just saying like now we have two people as opposed to just one. Yeah, I'm not sticking on arms on you, you know what I'm saying? I'm not changing you inherently. Yeah, I didn't know that was the problem. I'm just putting another one there, because why do I have to do that? Because I have two Cl's over here. So what does that mean? Since I have two, now, okay, now we want to count again over here. So how many chlorines and sodiums do I have? So remember, two times one is two, right? Okay, two times one is two, okay? So I have two of each one of those now. Now if I go over here, one times one is one, right? One times two is two, okay? So I have two Cl's over here, but I don't have two Na's. So how can I fix that? How can I fix that? Add a two to where? To here? No, to where? The front, the coefficient, right? Because two times one, why don't I add it here? Because then it would be what? What would it look like? It would look like this, right? Is that what sodium looks like? No, it doesn't look like that. It looks like what? It looks like this. I can't just stick. If I wanted to say, I need two heads, do I rip your head off and stick it on you? No, I don't do that. It doesn't make sense to do that. I say I need two heads. I want both of you to come with me, okay? That's what I'm saying, okay? Does that make sense? Okay. If it doesn't make sense, bust it out, okay? You're going to be doing this a lot, okay? That's a chemical change. Water of the H2O or whatever you want to call it? So, okay, as opposed to a physical change, let's just erase this really quick. That's all right. So a physical change, like the one we've been going over in class, right? Okay, notice. This is different than this, right? This, is that different than this? This one? That's different than this? Yeah. Is this different than this? Molecular formula? No. Uh-uh. It's not different, okay? So if it changes, then it's a chemical reaction, right? So, right? Did it change? No, they're the same, right? So it's not a chemical change. It's a physical change. Oh, one second. Look, this looks like this. This looks like this, right? Does that look like that? No. So does a chemical change happen? Does it look like that? No, a chemical change happens. Okay, these two things combined, right? But I have two of these. So, but this only has one. So I have to make another one of those things to, I don't have another, oh yeah, I do. Okay. So I have to have two of them, like that. So I have to have two of them, like that, right? And then I would have to have another sodium atom over here, which I don't have. You better. Do the owl? Just do the owl, yeah, well, whatever day it says, I can't actually remember what day.