 Okay, welcome back everybody. We are going to talk about our first type of organic molecule. I said there are zillions of different organic molecules in the world. You can put them into categories and we are going to talk about the first category or the first type of organic molecule. This type of organic molecule is called an alkane molecule. There are many different alkane molecules. They are the simplest organic molecules. They have only carbons and hydrogens, nothing else. They have all single bonds between the carbons and hydrogens, so CH4, this one that I showed you on a previous video, that is an alkane molecule. This one here, C2H4, that's not an alkane molecule because it has a double bond between the carbons. Alkane molecules are often used as fuels, some of them you've heard of, maybe. The names of alkane molecules end in the letters A and E. You may have heard of propane, that is an alkane molecule, you may have heard of octane in your gasoline, that is also an alkane molecule. The ten simplest alkane molecules, their names are listed here. The simplest one is called methane, second simplest one is called ethane, and on and on and on. If you notice, the parts that are highlighted in red are related to the words or the things that I wanted you to write down at the very beginning of the first video in this collection of slides. So it's probably a good time to break out that thing that you wrote down at the beginning of the first video. Here is the structure of methane. Methane we've already seen, we just called it CH4 in the previous video. Methane has one carbon, and that is why on that sheet that I wanted you to write on is the word meth, and it has the number one, because methane is the alkane molecule with one carbon. If you look, all single bonds here, and if you look none of the rules are being broken that we talked about in the previous video. Ethane is the next simplest molecule, the next simplest alkane molecule. This is its formula, and ethane has two carbon atoms, there they are. Everything else is a hydrogen. If you look, I'm not breaking any of the rules, and if you look they are all single bonded to each other. And it continues on like that. Propane is the next simplest alkane molecule, three carbon atoms, butane four carbon atoms, pentane five, hexane six. After that I got a little bit lazy and I didn't want to draw the other ones, but heptane has seven carbon atoms, octane eight, nonane nine, and decane ten. You should either memorize those or have them written on a sheet of paper because we are going to need those words for the rest of the videos. There's a problem though, there's always got to be a problem, otherwise I wouldn't have a job. The problem is this, suppose that you went up to me and you told me I am working with an organic molecule, and the formula is C4H10, and I said, ah, C4H10, you're working with butane, here's butane, that's what you're working with, and you look at me and you say no dumbass, I am not working with butane. The molecule that I am working with looks like this, and I say you see there's one, two, three, four carbons, so it's C4, and take my word for it, or you can count one, two, three, four, five, six, seven, eight, nine, ten hydrogens, C4H10. But this thing is not butane, because if you look at butane, four carbons are all in a row. If you look at whatever this C4H10 is, the four carbons are not in a row. There's three in a row, but then this carbon here kind of shoots off from the middle one. This is, in chemistry this is called a branch. In my speak I'm going to call it a side street, you'll see that later on. You can think of this as basically like a main road, and this is like a side road. In chemistry the formal way of calling that is a branch. But this is the problem, C4H10 is not good enough, this simple formula is not good enough to tell you whether you are working with butane or whether you're working with this molecule over here, because neither molecule breaks the rules. Every carbon in this ugly thing over here has four covalent bonds, every hydrogen in this molecule over here only has one covalent bond, so I'm not breaking any of the rules that I talked about previously, I'm not breaking any of the rules over here. So if someone came up to me and said I'm working with C4H10, I don't know which molecule they're working with. Are they working with butane, or are they working with this molecule over here? Because they're not the same because the atoms are attached in different ways. The problem that I'm trying to set up for you, the problem that I'm trying to introduce to you is that eventually the organic molecules get big enough that writing a simple formula is not good enough to tell you how the atoms are attached to each other. Once the molecules get big enough, formula isn't good enough to tell you the structure of your molecule. There's another word that I want to introduce to you here, and that is the word isomer. Isomers are two molecules with the same simple formula, but the atoms are attached in different ways. This molecule over here, which I drew a few minutes ago, it has the formula C4H10. Butane also has the formula C4H10, but the atoms are attached in different ways between the two of them, so we would say that butane and whatever this molecule is, they are isomers of each other, and that is going to come up throughout the rest of the course. This molecule has a name, we have not covered what its name is, but we will eventually, or eventually you will learn how to give it its proper name, but right now suffice it to say that butane and whatever this molecule is, they are isomers of each other, and the simple formula is not good enough to tell you which isomer you are talking about. Here, I'm just trying to emphasize it again, this is the same molecule that I drew on the previous slide, but I flipped it around so that the branch is pointing to the north. Pentane is an even bigger molecule, that's the alkane with five carbons in a row. Pentane has three isomers, there are three molecules that have this formula that are not the same as each other. So the bigger your organic molecule gets, usually the more isomers you can have. Pentane is an alkane with six carbons in a row, has this formula C6H14, C6H14 there are five molecules that have the same formula but different attachments, so it just gets worse from there. The bigger, in general the bigger your organic molecule, the more isomers you can have that have the same formula. So the punchline here is that the simple formulas that you and I are accustomed to, they aren't good enough descriptions to tell you what type of organic molecule you have all of the time. So we need to come up with a better way to describe organic molecules to each other, and there's a bunch of other ways of doing this, and on the next video what I'm going to do is I'm going to cover most or all of those ways. So I will see you in the next video.