Now oxides, peroxides and superoxides are binary compounds of oxygen with metals. Now here we're going to say that group 1A and 2A metals combined directly with oxygen to form these three types of compounds. So let's take a closer look at oxides, peroxides and superoxides.
The memory tool that we can use here is that oxides, peroxides and superoxides are 1221. So what exactly do we mean by that? Well, first of all, oxides, peroxide, superoxides, OPS. Remember, remember it in that order. And remember it's alphabetical as well. We're going to say here that the one here tells us the number of oxygen, so we have one oxygen and the second number gives us the charge. So two here would be two minus. And we know what's minus because all of these are anions.
So coming back down here, the first number gives us the number of oxygens, the second number gives us the charge. Let's move over to peroxides. Peroxides. Its first number is this 2 now, so there's two oxygens. The second number gives us its charge 2 minus, so peroxides are O2⁻2. Superoxides. The first number gives us the number of oxygens, which is 2 oxygens. The second number gives us its charge -1. So superoxide is O2⁻.
So these are the formulas for our oxides, peroxides and superoxides. Remember OPS written in alphabetical order. First number represents the number of oxygen, second number represents the charge for each of them. If you can remember that, you remember the structures of each one of these anions.