To draw the Lewis structure for NO3–:
| Group 15 N(5 × 1) | 5 electrons |
| 3O (6 × 3) | 18 electrons |
| one negative charge | +1 electron |
| total electrons available | 24 electrons |
| used in three single bonds | -6 electrons |
| used completing octets at O | -18 electrons |
A double bond between nitrogen and oxygen completes the octet at N. The structures shown above are referred to as resonance forms.
Resonance forms have the same arrangement of atoms but a different arrangement of electron pairs. Note that two additional resonance forms can be drawn which involve each of the other oxygens in turn in a nitrogen-oxygen double bond.