Up to this point, we've just examined polyatomic ions that possess a negative charge. Now it's time to look at the positively charged ones. We're going to say most polyatomic ions are negatively charged except for NH4+ ion and Hg22+ ion. We're going to say NH4+ (Ammonium ion) is the only major polyatomic ion that you're going to need to know that has a plus one charge.

Then, we're going to discuss Hg22+. And know that the little 2 is not a typo. What this is, it's two individual Hg+ mercury ions. They combine together, so now there are two of them together, and their combined charge comes out to 2 plus. Because each one possesses a plus one charge, we're going to say this is called mercury(I) ion. Yes, I know it might be a little confusing because the charge is 2 plus, but realize that the 2 plus comes from the fact that each mercury is plus 1.

So again, a vast majority of the polyatomic ions you're going to encounter possess a negative charge. These two possess positive charges.