 Okay, methionine, one of the 20 amino acid building blocks from which proteins are made, has the following backbone structure, okay? So all that's missing are the hydrogens. And every carbon, as we know from the last problem, can make four bonds. Every oxygen can make two bonds. Every sulfur can make two bonds. And every nitrogen can make three bonds, okay? So they want us to figure out what is the molecular formula of methionine, okay? Think you guys can do that? So the only thing we're missing on this thing is hydrogen. So let's write down what the problem said. So it said carbon is four bonds, the number of bonds. It said oxygen was two, sulfur was two, and nitrogen was three, okay? And it wants us to give the molecular formula of this thing. So let's just go around and find atoms that don't fulfill their bond requirement. Is everybody okay with what we're doing? So I'd just like to start from one end of the molecule doing this. And I see here this oxygen only has one covalent bond to it. So that must mean it needs another covalent bond. If the only thing we're missing is hydrogens, then that's where one of the hydrogens is gonna go. So let's write it in, okay? So all the double bonds should already be filled by now. Yeah, so we'll get progressively harder ones, but for right now, all the double bonds will be filled, okay? So now this oxygen has two covalent bonds, right? So this oxygen, as you alluded to, right, has also two covalent bonds because the double bond equals two single covalent bonds. There are differences which we'll learn is that a double bond's stronger and shorter than a single bond, but it's composed of four electrons as opposed to two electrons, if you recall us, we're making the bonds. So this carbon has four covalent bonds around it as well because it's got one, two in the double bond, three, four. This carbon is missing one bond. Is everybody okay with that? So let's put hydrogens. The nitrogen, we said, three bonds. So it's only got one. So it needs two bonds. Hydrogen can only make single bonds. So don't try to make double bonds. I know I could see the question brewing in your head. Don't try to make double bonds with hydrogen. I did say something. Yeah, yeah, so it's because I was making up this problem in my head, so forgive me, I apologize. No, no, I mean, I apologize to the world. It's hard, it's always hard to say everything in a problem that you're making up. But yeah, double bonds cannot be made by hydrogen. Triple bonds, which you'll find is another type of bond that you'll see cannot be made by hydrogen. Only has two single bonds, so we're going to have to make. I'm just gonna go down the line. Sulfur already has two, so we're cool with that. This carbon needs three. So now, it wants us to tell it what is the molecular formula of my five. So it doesn't really matter how you put these things in order. I usually will put carbon, hydrogen, oxygen, and then all the other ones, okay? That's the convention. So let's do it that way. So carbon, one, two, three, four, five. So C five, H one, two, three, four, five, six, seven, eight, nine, 10, 11, two, and there's no standard order to put those in. And if you put SN or SN02 or something like that. Questions on that one? So you guys think you can do these kind of fill in the hydrogens if I give you the rest of the scale of the structure.