 Okay, this is a continuation of the discussion of covalent bonding. If you remember, covalent bonding is sharing of two electrons, or a covalent bond is sharing of two electrons between two atoms. We're going to talk about what I'm calling fancier covalent bonding. So let's get to it. Here are three different atoms, all somewhat unstable, not completely unstable, but a little bit. So I'm going to give them all frowny faces. They're all neutral as well. They're all electrically neutral. This is an oxygen, carbon, and an oxygen. Because they're neutral, the oxygen has six valence electrons and two empty slots in its outermost energy level. So does this oxygen on the right has two empty slots, and this carbon actually has four empty slots. And there they are, and the oxygen has four valence electrons. The reason that they have the empty slots that they have, if you remember, is that the second electron energy level can hold a maximum of eight electrons. So the oxygens have six of the eight, so two empty slots. The carbon has four out of the eight seats filled in the second energy level, so it has four empty slots. So you can ask, well, how can I get these atoms to be more stable? The obvious answer, since we are talking about covalent bonding, is to get them to share. And so if I get them to share, basically, let's say that this oxygen over here says, look, I'll let you borrow my electron. Please return the favor. This oxygen on the right does the same thing. This is, look, I'll let you borrow this electron. Mr. Carbon-Adam, please let me borrow one of your electrons as well. And if they do that, you end up with this situation drawn down here. Now let's look at it. The question is, the ultimate question is, are they stable the way that this is? So let's look at the electrons, the outermost electrons in this oxygen now. How many are there? One, two, three, four, five, six, seven. That means that we still have one empty slot with that oxygen. Still unhappy. Let's look at this oxygen on the right. One, two, three, four, five, six, seven. Also has one empty slot in its outermost energy level. Also unstable or unhappy still. Let's look at the carbon. Let's not forget about the carbon in the middle. Here are all of its electrons, including the ones being shared. One, two, three, four, five, six. This one still has two empty slots. So also still unstable, unhappy. So our experiment kind of looks like it backfired. Looks like it didn't work. Sharing, oh my God, that's horrible. Sharing didn't help, or at least it looks like it didn't help. The issue is, though, you can get them to be stable if you make them share more. So basically, this oxygen on the left is sharing, the oxygen on the left and the carbon in the middle are sharing two electrons. The oxygen on the right and the carbon in the middle are also sharing two electrons. What they can do is they can share even more. In other words, this oxygen can share its electron with the carbon in the middle and the carbon can return the favor. Same thing with this oxygen. It can share with the empty slot over here and this carbon can share with the other empty slot that the other carbon has. If you do that, everybody becomes happy or stable, if you want to call it that. This oxygen on the left, let's count how many electrons it has, including the ones being shared. One, two, three, four, five, six, seven, eight. No empty slots means that it's relatively stable. This oxygen on the right, same situation. One, two, three, four, five, six, seven, eight. No empty slots. So it's also somewhat stable or somewhat happy. Carbon in the middle. Remember, we're counting all of the electrons including the ones being shared. One, two, three, four, five, six, seven, eight. Also no empty slots. And so this, if I gave you a bunch of oxygen atoms and some carbon atoms and I said follow the rules. Don't break the rules that we've been talking about for the past week. Get them to share electrons so that they become stable. And show me the simplest molecule you can make. This is basically about the simplest molecule that you can make. And those of you, there are probably some of you out there who know what this is. This is a single carbon, there it is, and two oxygens. So the simple formula for this molecule is CO2. This is also known as carbon dioxide. If I gave you those atoms and I said build me something simple that doesn't break the rules, there's a good chance that you would come up with this. So we can figure out how a lot of important molecules are assembled, how the atoms are attached to each other just by following these rules. You can figure out that the carbon and carbon dioxide is in the middle. The oxygen atoms are on the edges. Not only that, but this is a single covalent bond. This is a single covalent bond. But there are two sets of them in carbon dioxide. So you can realize, in addition to what we just said about the carbon being in the middle and the oxygens on the edge, you can realize that the attachment between carbon and oxygens is actually a double covalent bond. And that's what I meant by fancier. That is extra sharing, or twice as much sharing as you have between the atoms and water. This is also called a double covalent bond. So remember, one covalent bond is two electrons being shared. This is four electrons being shared. So it's usually called a double covalent bond. In the way that you draw it with the lines, you could draw it with four dots and four dots. Alternatively, one of the more common ways is to draw two parallel solid lines. I guess it looks like an equal sign. This is also a very common way of drawing a double covalent bond. And if you take enough chemistry, you will see that an awful lot. So this is water, and these single solid lines mean one covalent bond, or usually probably the more formal way to call it is a single covalent bond. Two lines between two atoms is called a double covalent bond, and that means four electrons are being shared. So that's what I mean by fancier covalent bonding. You can share even more, actually. You can look at this molecule. These are two nitrogen atoms sharing six electrons. So how many covalent bonds is that? Well, every two electrons being shared is one covalent bond. So between these two nitrogens, we have one covalent, two covalent, three covalent. This is called a triple covalent bond. And if you were going to draw the attachment using those solid lines, what you would do is you would draw three solid lines parallel to each other, and this is probably the most common way of showing a triple covalent bond. So you should know that. You should know how to draw a single covalent bond. You can either draw it with two dots or two valence electrons being shared, or you can draw it with a solid line. You should know double covalent bond. So that is four electrons being shared, or you could draw two parallel solid lines between the atoms. It means the same thing. And over here, that is a triple covalent bond. This is also another way of showing people a triple covalent bond. All right. So that is the end of the introduction to covalent bonds. There's still another video or two left. I'm not sure how many I need to pump out. But I want to recap a little bit of what we've gone over as far as bonding is concerned. The recap starts here. There are two major types of bonds, two major types of ways to connect atoms to each other. There are ionic bonds that is basically controlled by the electrical charges that different atoms can have. If you have atoms with opposite electrical charges, they will be attracted to each other and under the right conditions, they'll stick together. There are covalent bonds, which we are just finishing up talking about. That is when electrons are shared between atoms and because they're constantly sharing, they end up stuck to each other. Both types of bonds, both types of attachments, are controlled by valence electrons. If you notice, when we've been doing all of these covalent bonding pictures, all we've ever been drawing are the dots around the symbol, and the dots around the symbol means just valence electrons. It's not counting the inner electrons as far as that's concerned. Same is true with the ions. The electrical charge that atoms prefer to have is controlled by either gaining electrons in the outermost energy level or losing them and making a charge that way. But the outermost energy level is called the valence level, so ionic attachments are controlled by valence electrons as well. So valence electrons let you figure out how many ions are going to attach to each other in an ionic compound, and they also let you figure out how many atoms are going to covalently share or share electrons with each other. So it lets you figure out how atoms are attached in many different molecules, especially for the first three rows of the periodic table. That's it for introduction to covalent bonding. There is at least one other video coming up that is related to covalent bonding, but it's only indirectly related. So that's it for the moment.