 Okay, so homo-atomic molecules, we actually, since they're the same atom, they're only composed of one atom, we actually consider these the elemental forms of these, well, elements. These molecules are the elemental forms of these elements. So there are actually a few of these elements that are very common in diatomic form. And it's useful to know these particular ones. So it's one of the lists, I guess, that you should quote unquote memorize. Eventually you'll learn how to build the structure and you won't necessarily have to memorize it. Before the first exam it's pretty good to memorize. But anyways, there's a few of these that you want to know. So specifically diatomic, homo-atomic gases, usually they're gases. Some of them, like iodine, aren't. But they exist in equilibrium. But we call these the elemental forms. Okay, so these diatoms are elemental forms. So some common ones are H2O2, like we said, oxygen. If you're familiar with, if you want to know the structure of oxygen. And again, you'll learn how to build those later. Nitrogen's another common one. So if you go down the periodic table, right, you'll see oxygen, nitrogen. And we'll talk about these lines in between these atoms. So these are the atomic symbols, of course. We already said these little dots are called lone pair electrons, which we'll get into later. These lines are called bonds. In between these atoms we have here a single bond, a double bond, and a triple bond. Again, it's something that's out of the scope of what you need to know right now for the exam or for chapter one or whatever. But it is good to realize that there are structures. These molecules do have a structure associated with them. And then all the halogens, which are the ones group seven. So chlorine, chlorine, bromine, and iodine. So we just usually go with the four common halogens. And they all look very similar to hydrogen, except they've got three lone pairs around them, around each of the atomic symbols. So chlorine looks like that. Chlorine focus to chlorine. So it's got that single bond, like we said, and then the three lone pairs around each one of those atoms. Again, it's something you don't need to necessarily know right now, but since we're learning something, we might as well learn as much as we can. And iodine or iodine, however you want to say it. Okay, so as you can see, like if you go along with periodic table, it kind of looks like that. Hydrogens over way over here. In fact, hydrogen sometimes you can think of as all the groups seven we call halogens. I guess we should write that up here, halogens. Something else you're going to want to know. Hydrogen kind of interlopes with the halogens, as well as the group ones. So it looks very similar to these other guys. So these are the, well let me say, one, two, three, four, five, six, seven. The elemental forms are the diatomic elements. Okay. A lot of times you'll hear them called the diatomic gases, but bromine and iodine really aren't gases. Bromine's a liquid and iodine's a solid. Although, you know, they do exist in equilibrium with their gaseous form. If you have them in a sealed container, you can see it fairly readily. So just a list to memorize. Something good, like I said, to memorize for the first exam. Okay.