What is the charge on the polyatomic ions nitrite and chlorite?
Both have a charge of
This is the nitrite ion, in Lewis structure form. Notice how one oxygen has 6 valence electrons and the nitrogen ion has 5 valence electrons and are paired with that many electrons, so they both have formal charges of 0. The other oxygen, on the other hand, is assigned 7 electrons so its formal charge is
This leaves the nitrite ion with an overall charge of -1.
Chlorite is similar in that the chlorine atom and one oxygen atom have formal charges of 0, but one oxygen atom has a formal charge of -1.
Another way to interpret the charge of -1 is that both ions have an extra electron, or one more than the molecules normally would have.