HNO3 Lewis Structure
Nitric acid · A strong acid used to make fertiliser and explosives.
The HNO3 Lewis structure has 24 valence electrons, drawn as two N–O bonds, one N=O bond and one bond to hydrogen, with seven lone pairs in total. The central N is sp2 hybridized, which makes it a trigonal planar molecule with a bond angle of 120 degrees. HNO3 is polar: the O-H bond dipoles do not cancel in this shape, leaving a net dipole. There are two equivalent resonance structures.
- 24 valence e−
- trigonal planar
- 120° bond angle
- sp2
- polar
Calculated properties
| Total valence electrons | 24 |
|---|---|
| Bonding electrons | 10 (5 shared pairs) |
| Nonbonding electrons | 14 (7 lone pairs) |
| Lone pairs on N | 0 |
| Electron domains (steric number) | 3 |
| VSEPR notation | AX3 |
| Electron geometry | trigonal planar |
| Molecular geometry | trigonal planar |
| Bond angle | 120° |
| Hybridization | sp2 |
| Polarity | polar |
| Formal charges | N: +1, O: -1 |
| Resonance structures | 2 |
| Molar mass | 63.012 g/mol |
How to draw the HNO3 Lewis structure
-
Count the valence electrons
Add up the outer-shell electrons every atom brings. That total is the budget for the whole structure - every line and every dot has to come out of it, and nothing may be added.
1 (H) + 5 (N) + 3 x 6 (O) = 24 valence electrons -
Work out what is bonded to what
This is an oxyacid. Every oxygen bonds to the central N, and the acidic hydrogens sit on oxygen, not on N.
-
Join everything with single bonds first
Every connection starts as one shared pair. Draw them all before worrying about double bonds - the arithmetic in the next step is what tells you where the double bonds have to go.
4 bonds x 2 = 8 electrons used, 16 left -
Work out how far short you are
Add up what every atom still needs to fill its shell - eight electrons for most atoms, two for hydrogen - minus what its single bonds already give it. Compare that with the electrons you have left. The difference decides everything that follows.
needs 18, has 16, short by 2 -
Turn the shortfall into multiple bonds
Being short means atoms have to share more. Every pair that moves from a lone pair into a bond counts twice - once for each atom - so a shortfall of 2 is covered by 1 extra shared pair. That is where the double bond comes from.
N=O3 -
Fill in the lone pairs
Every electron not in a bond sits as a lone pair on an atom. Each atom takes exactly what it needs to finish its shell - there is no choice left at this point.
O1: 2, O2: 3, O3: 2 (14 electrons) -
Check the central atom
N ends up with a full octet. Every electron in the budget is now placed.
N: 8 bonding + 0 nonbonding = 8 -
Check the formal charges
Formal charge is valence electrons, minus lone-pair electrons, minus the number of bonds. They are not real charges, but they have to add up to the overall charge on the species, and a structure that keeps them small is the better one.
N: 5 - 0 - 4 = +1 ; O2: 6 - 6 - 1 = -1 -
Work out the shape
Count the electron domains on N: 3 bonded groups. A double or triple bond still counts as one domain, because it points in one direction. That gives trigonal planar electron geometry; ignore the lone pairs and the atoms themselves sit in a trigonal planar arrangement.
steric number 3 -> sp2 -> trigonal planar, bond angle 120 -
Decide whether it is polar
The O-H bond dipoles do not cancel in this shape, leaving a net dipole.
dipoles do not cancel -> polar
Resonance structures
More than one drawing gives the same electron count and the same formal charges, and no single one of them is the real molecule. HNO3 is an average of the 2 structures below, which is why bonds that look different here are actually identical in the real molecule.
Is HNO3 polar or nonpolar?
HNO3 is polar. The O-H bond dipoles do not cancel in this shape, leaving a net dipole.
| Bond | Electronegativity difference | Character |
|---|---|---|
| O–H | 1.24 | polar covalent |
| N–O | 0.40 | polar covalent |
Common questions
How many valence electrons does HNO3 have?
HNO3 has 24 valence electrons. 10 of them are in bonds and 14 sit in lone pairs.
What is the molecular geometry of HNO3?
HNO3 is a trigonal planar molecule. The central N has 3 bonded groups, a steric number of 3, which gives trigonal planar electron geometry and a trigonal planar molecule.
What is the bond angle in HNO3?
The bond angle in HNO3 is 120 degrees. That is the ideal trigonal planar angle, and nothing distorts it here.
What is the hybridization of HNO3?
The central N in HNO3 is sp2 hybridized. Steric number 3 means 3 orbitals have to be mixed, which is exactly what sp2 gives you.
Is HNO3 polar or nonpolar?
HNO3 is polar. The O-H bond dipoles do not cancel in this shape, leaving a net dipole.
Does HNO3 have resonance structures?
Yes. HNO3 has two equivalent resonance structures. The real molecule is not any one of them - it is an average, so every bond that differs between the drawings is really the same length in the actual molecule.