 Okay, let's try to do this problem now. Just naming these different ionic compounds. It looks like most of them are transition metal polyatomic ion compounds, okay? So you're going to have to know the name and chemical formula and charge of the polyatomic ion in order to do these types of problems, of course. Cobalt, I'm going to give you a periodic table, so you won't need to know cobalt for right now. But cobalt is going to be CO. And since it's cobalt 2, you know that it's plus 2. So since it's a transition metal, it's got this Roman numeral there, and that Roman numeral tells you what the ionic charge is. Remember transition metals are always positively charged, okay? And then you just got to memorize what phosphate is. Phosphate is this ion here, CO4 3 minus. Okay? And then just like any other ionic compound, when you make the formula unit, you want the charges, the positive charges, the balance with the negative charges, okay? So the only way or the lowest way to get 2 and 3 to balance is to put 2 times 3 is 6. So if you have 3 cobalts, that's going to give you a positive 6 charge. And then phosphate, of course, if you multiply 3 times 1 equals 6, that's going to be 2. Okay? So you've got to know really the charge of phosphate there. Okay? So then you see we've got plus 6 here, minus 6 there. So just combine those two to make CO3. And then with polyatomic ions, you want to put them in parentheses to emphasize, of course, and indicate that they are one unit. Okay? And then just put the 2 as the subscript there. Okay? So does that make sense on how to do that one? I think so. Okay. Cool. Let's do this one here. And hopefully it'll make even more sense. Okay, cobalt 2, again, it's the same thing. You know that it's going to be CO2 plus, okay? Because of the Roman numeral there. And oxide, oxygen, you should know by now since it's in group 16 elements there, it's going to have a negative 2 charge, so O2 minus there. And then again you want those cationic and anionic charges to balance. 2 and 2, 2 minus 2, of course, balances. So this compound is going to be COO, like that. Barium permanganate. Okay, permanganate, this is another polyatomic ion. Its structure is, or its formula is MnO4 minus. Okay, so that's just something you're going to have to memorize. And barium, if you look at the periodic table, you see that it's a group 2 element or an alkaline earth metal. All those group 2s always have a plus 2 charge, okay? So we're going to have VA2 plus and MnO4 minus there. So remember we want to balance these charges. Okay, so we got 2 plus and 1 minus, so we're going to need another minus sign. And how to do that? Well you just get another MnO4, so by doing, put a 2 there. And then when those 2 things come together, we get VA MnO4. And then that 2 goes down as a subscript, like that. So that's barium permanganate. Calcium nitrate, again it's similar to this barium permanganate. Nitrate is another polyatomic ion, MnO3 minus. Okay, so you're going to have to remember that. And you're going to have to know, again, your polyatomic ion. Okay? And then calcium, again, is a 2 group 2 element. So we got 2 plus there. So you see it's similar as barium permanganate was 2 plus 2 to minus 1 plus 2 to minus 1. So you just put a 2 in front of that nitrate. And then when you make the formula unit, of course, you're going to have calcium N032. So that's calcium nitrate. Iron II sulfate. Iron II, well iron is a transition metal. That's why it's got this Roman numeral after it. Iron's atomic formula is F8. The 2 indicates that it's going to be 2 plus. Sulfate is something you're going to have to remember. It's SO4 2 minus, like that. And hopefully you can see that plus 2 and minus 2 will cancel each other out. So all you got to do in this one is write FESO4. Okay? Notice in this one we didn't put parentheses around the polyatomic ion. And that's due to the fact that there's no subscript after it. Okay? So there's not two of them or three of them like we have in the previous problems. Well, two of them in each of those previous problems. Okay? Does that make sense?