Nitric acid contains an H–O–N framework. Nitrogen is bonded to three oxygens, one oxygen carries the hydrogen, and resonance exchanges the N=O double bond between the two non-hydroxyl oxygens.
The O–H bond stays fixed; resonance involves the other two oxygens
Total valence electrons24
Central atomNitrogen
Geometry around NTrigonal planar
Approximate angle≈120°
HNO3 Lewis structure overview
Hydrogen contributes one valence electron, nitrogen contributes five and three oxygens contribute eighteen, for twenty-four total. Hydrogen attaches to oxygen because oxyacids contain an O–H group. Nitrogen is the central atom connected to all three oxygens.
How to draw the HNO3 Lewis structure
Count 24 valence electrons.
Add 1 from H, 5 from N and 18 from the oxygen atoms.
Build the H–O–N skeleton.
Connect nitrogen to three oxygens and connect hydrogen to one oxygen.
Complete terminal octets.
Add lone pairs to oxygen while respecting the total electron count.
Form one N=O double bond.
Move a lone pair from a non-hydroxyl oxygen into the N–O bond so nitrogen reaches an octet.
Draw the second resonance contributor.
Move the double bond to the other non-hydroxyl oxygen and transfer the -1 formal charge accordingly.
Formal charges
Nitrogen carries +1 in each major contributor. The singly bonded oxygen that is not attached to hydrogen carries -1. The hydroxyl oxygen and double-bonded oxygen are neutral. The overall molecule remains neutral.
Geometry and bonding
Nitrogen has three bonding domains and no lone pair, giving trigonal planar geometry around N. The two non-hydroxyl N–O bonds are equivalent in the resonance hybrid, while the N–O(H) bond is distinct.
Common mistakes
Bonding hydrogen directly to nitrogen rather than to oxygen.
Moving the O–H bond when drawing resonance contributors; only electrons move in resonance.
Giving nitrogen more than eight electrons. Nitrogen is a second-period element.
Omitting the +1 charge on nitrogen or the -1 charge on a singly bonded non-hydroxyl oxygen.
Frequently asked questions
How many resonance structures does HNO3 have?
There are two major equivalent contributors involving the two oxygen atoms that do not carry hydrogen.
Why is hydrogen attached to oxygen?
Nitric acid is an oxyacid, and its acidic hydrogen is part of an O–H bond.
Is nitric acid planar?
The atoms around nitrogen are approximately trigonal planar; the molecule is commonly treated as largely planar around the nitrate-like group.