A polyatomic ion is a charged particle which has two or more atoms held together by covalent (sharing of pairs of electrons) bonds
1. Ions that end in ate have oxygen in them.
2. Elements in the same family make similar ions. So for example if you know chlorate, you also know bromate and iodate too (BrO3-, and IO3-). There are some exceptions. Nitrate is not like phosphate even though nitrogen and phosphorus are in the same group. However arsenate is like phosphate. (But bismuthate is like nitrate! How exasperating!)
3. If you remove one oxygen atom from the ate form of the ion, the suffix changes to ite. Examples: Nitrate is NO3- but nitrite is NO2-. Similarly phosphite PO33- has one less oxygen than phosphate PO43-.
The prefix hypo removes one more oxygen from the (ite) ion, and the prefix per adds an additional oxygen to the ate ion. For example:
(But iodide is just I-)
4. If you bond H+ to an anion, you add +1 to the charge (that makes sense) and add hydrogen to the name. So since carbonate is CO32-, hydrogen carbonate is HCO3-. Ions that have a -3 charge can take 1 or 2 hydrogens. When two hydrogens are added the prefix di is used, so HPO42- is hydrogen phosphate and H2PO4- is dihydrogen phosphate. You may know HCO3- as bicarbonate. This way of naming uses the prefix bi to indicate the addition of hydrogen ("bi" here has nothing at all to do with "two"). The use of "bi" is archaic but still quite common and you should be familiar with it. What do you think is the formula for bisulfate?
5. Finally, in some ions sulfur replaces one of the oxygen atoms and then "thio" is added as a prefix to the name. Thus SCN- is called thiocyanate after the cyanate ion (CNO-) and thiosulfate is S2O32- after sulfate.