 Okay, the next two slides are just there to get you to become accustomed to looking at how you will see different ions written. This slide is showing you a bunch of different cations, and if you remember cations are atoms or groups of atoms that are positively charged. So this is a lithium ion, it's a lithium cation in particular. And if you just see a single plus, that means that the lithium has a charge of plus one. This is a sodium cation, also charge of plus one, potassium as well. If you have a different ion, like this magnesium ion, that has a different charge, then you have to write the number. So this particular magnesium cation has a charge of plus two. So does this calcium, and this aluminum has a charge of plus three. Again, you don't really need to memorize these. You just need to sort of be able to recognize what this number in the upper right is telling you. This slide is showing you some common anions. This is not an exhaustive list of anions. The list of cations on the previous slide is also not an exhaustive list. They're just examples of different ions. This is a fluorine ion, and again, because there's no number written next to the negative sign, that means that this fluorine ion is charged at negative one. This is a chloride ion, also charged at negative one. This one is at negative one. This iodine is at negative one. And again, if you have to write a number, or if you have a number other than one, then you have to write the number. So this oxygen has an electrical charge of negative two. There's something a little bit formal about this. F is the symbol for fluorine. However, when it becomes negatively charged, you drop the I-N-E and you add I-D-E. So when it's charged, it's called a fluoride ion instead of a fluorine ion. And I'm pretty sure I sort of said both things. I said it the correct way and the incorrect way. But it doesn't really matter. I'm just sort of telling you to tell you just in case someone ever corrects you. This is called a chloride ion, et cetera, et cetera. It's perfectly fine if you call this a chlorine ion, in my opinion. Again, I don't want you to memorize this stuff. I just want you to realize that if you see a negative sign or a number with a negative sign in the upper right of a symbol, that means you have an anion. And that means your ion is negatively charged. OK. So now I want to talk about the fact that ions that have opposite electrical charges, if you have some ion, and so I'm going to just call it x with a plus charge and some other ion, which I'm going to call z with a minus charge, if you have ions that have opposite charges, they'll be attracted to each other. And they will stick together and they will make some material, in this case, maybe the formula would be xz. And when ions stick together, they're called ionic compounds. So I'm going to teach you a rule about how to make or how ionic compounds are made. Here's the rule. Ions, as far as we're concerned, we can remove the almost. Ions always combine to make a net electrical charge of zero. In other words, they will attach to each other in numbers that will cancel each other's electrical charge out. And when you write the formula of an ionic compound where the electrical charges are canceled out, it's customary to write the one with a positive charge on the left side. So for table salt, there's sodium, which is charged at plus one, and chloride, which is charged at minus one. And because the sodium is positively charged, the chloride is negatively charged. They're attracted to each other and they stick together and they make an ionic compound called NaCl. Let me clean that up. Even worse, there's NaCl. And if you'll notice, this sodium has a charge of plus one. This chloride has a charge of minus one. But together, the one plus and the one minus cancel each other out. So the formula for sodium attaching to chlorine is a single sodium attaching to a single chlorine. You'll notice that there's no number in the lower right, which means there's one of each implied to be there. So let me show you again. There's sodium. There's chloride. You need one sodium and one chloride to cancel each other's electrical charge out because the sodium is at plus one, the chloride is at minus one. Here's a different situation. Magnesium comes. The magnesium ion comes with a charge of plus two. The chloride ion comes with a charge of minus one. And there is a material out there in the world called magnesium chloride. You don't really need to know this name, but I'm trying to illustrate a point. And it's an ionic compound. And it's made of magnesium ions and chloride ions stuck to each other. But if you wanted to know what the formula is, it's going to be mg some number attached to chloride, some other number. The question is, what are these numbers go in the place of those question marks? To figure that out, you have to go back to this rule and say, well, ions combine so that they cancel each other's charge out. So if I had one magnesium, the magnesium brings me a charge of plus two. And I mixed it with one chloride. The chloride brings me a charge of minus one. The question you ask yourself, if these two stuck together, one and one, would they cancel each other's charge out? The answer to that is no, because the magnesium has two pluses and the chloride only has one minus. So if I took one of each and stuck them together, the whole charge of this blob that got stuck together is still going to be plus one. But we need to get it to zero. So you can say, well, how many chlorides do I need to actually cancel out the charge of one of these magnesiums? It's not one chloride, I need two of them. So imagine that I had another chloride stuck here as well. And all three of these ions now make one big blob. The magnesium has a charge of two pluses. Each chloride has a charge of one minus, but together they have two minuses that can cancel out the charge of this magnesium over here. So if I have two chlorines and one magnesium, then the whole charge of that blob is going to be zero. And because of that, if I wanted to know what the formula was for magnesium chloride in this blob, it's one magnesium. So over here, I'm going to put a one, that's a horrible one. And how many chlorides are here? There are two of them. So the formula for magnesium chloride is Mg1Cl2. Most of the time, you would never write the number one there, because if it's a one, you can omit it. So the formula for magnesium chloride is going to be MgCl2. And the reason is because you need two chlorides to cancel out the electrical charge of one magnesium. And so if you know the charges of different ions, you can figure out what the formula is for the ionic compounds that they might make. For sodium and chlorine, I just need one of each, because the charges are plus one and minus one. So the formula for sodium chloride is going to be Na1Cl1. But nobody ever writes the ones, so you just write NaCl. Let's do another one. We're going to beat this to death. Calcium has a charge of plus two. Sodium has a charge of plus one. And we want to know how many calciums attached to how many sodiums. What's the formula? This is a trick question. They don't attach to each other, because they both have positive charges. So these things are going to repel each other. They don't make an ionic compound. So you can figure this out as well. This is basically an unanswerable question, because two positive charges are not going to make an ionic compound. Here's maybe a simpler or different version. Sodium comes with a charge of plus one. This is called oxide when it's negatively charged. It has a charge of negative two. So you have to ask yourself, what's the formula for sodium oxide? It's going to be Na question mark, O question mark. How many sodiums and how many oxygens do I need when they come with these charges to cancel each other's electrical charge up? You can guess. You can say, well, I need one sodium. That's plus one. And I need one oxide. That's minus two. Oops, go away. If that happens, if I have one of each, do the electrical charges cancel each other out? No, because I have two negatives from the oxygen, and I only have one positive from the sodium. So that doesn't work. The formula for sodium oxide is not one and one. You could say, well, which one is not bringing enough charge? And it's the sodium. So you can say, well, what if I have two sodiums? Each of them gives me a charge of plus one. And I have one oxide. That gives me a charge of minus two. Does this entire blob of three ions have a total electrical charge of zero? And the answer to that is, yes, it has a charge of zero, because the oxide has two negatives. And each sodium, I have two of them. Each one has a charge of plus one. So that's two positives. Two positives, two negatives gives you a charge of zero. So if you wanted to know what the formula was for sodium oxide, it's two sodiums. So it's Na2 and a single oxygen, O. There's the formula for sodium oxide. And again, you can figure it out just by playing this game of trying to get the ions to match up so they cancel each other's charge out. Here's the last one. Magnesium comes charged at plus two. Oxygen comes charged at minus two. So I want to know what the formula is for magnesium oxide. You can pause the video if you want and try this out. Unpausing, I would say, if I mix one magnesium, charge at plus two, and one oxide charged at minus two, do they cancel, does the entire blob have a total charge of zero? And the answer is yes, because they have equal and opposite charges. And so the formula for magnesium oxide is just one magnesium. You don't have to write the number one and one oxygen. You don't have to write the number one again. So again, it doesn't really matter what the electrical charges are, as long as you can get them to balance out all of a bunch of positives balanced out by an equal bunch of negatives, then you'll be able to figure out the formula for ionic compounds. So that's it for ionic compounds, or at least the beginning of ionic compounds. There will be more coming up in the next video.