Now the other polyatomic ions don't fit into predictable patterns and so must be memorized. So we're going to start out first with the other Tetra oxides. Now these are called the others because they don't quite fit in with the other two major Tetra oxides we've covered in sulfate and phosphate. Now permanganate permanganate's formula is MnO4-, 1. Then we have chromate which is CrO42- and then finally oxalate which is C2O42-.
Now remember, they're all tetraloxides because they all possess 4 oxygen, but we call them the others because we have manganese, chromium and carbon. These elements are in different places on the periodic table, so it's hard to form a real pattern with them. Then we have the other polyatomic ions. We don't really classify them as trioxides or Tetra oxides because some of them don't possess that many oxygens or any oxygens at all.
So here we have cyanide. Cyanide is CN-. We have hydroxide, which is OH-, peroxide, which is O22-. So kind of reminds us a little bit of mercury one ion where we have in this case 2 oxygens, each one is -1, so collectively they're 2 minus. Then we have dichromate, which is a little bit similar to chromate, so dye meaning that we kind of double things a little bit, but here it's Cr2O72- instead of O8.
Then we have cyanate which is related to cyanide. Cyanate is CNO- and actually it's OCN-, the correct way to write it. So sine I doesn't possess an oxygen, cyanate does possess an oxygen. Then finally we have acetate. Ion acetate is written as C2H3O2-. Now this will be the predominant form that you will see, but later on in chemistry you may see them showing in another form. You may also see it as Chapter 3, COO-. So just keep your eyes open when you see either form. Both of them represent the acetate.