Question

How would you draw all of the resonance structures for nitrate?

Answer 1

By exchanging the electron pairs around the oxygens.

Explanation:

The nitrate ion has three resonance contributors.

Nitrate anion possesses 3 formal charges on its atoms.

The nitrogen atom is quaternized (and thus formally positive) in all the representations.

We can consider the double-bonded oxygen to be neutral, and the other oxygens bear formal negative charges; of course, all the oxygen atoms are equivalent by resonance.

We add these 2 negative charges to the formal positive charge on nitrogen and come up with a formal negative charge for the anion, as required.

Of course, all of the `"N-O"` bonds would be the same length (approx. `"1.27 Å"`, compared to an `"N-O"` bond in `"NO"_2`, approx. `"1.20 Å"`, which has a higher bond order.