NO2− Lewis Structure
Nitrite ion · The curing agent in processed meat, and an intermediate in the nitrogen cycle.
The NO2- Lewis structure has 18 valence electrons - the 1− charge adds one, drawn as one N–O bond and one N=O bond, with six lone pairs in total, all inside square brackets. The central N is sp2 hybridized, which makes it a bent ion with a bond angle of 119 degrees. The 1− charge does not sit on one atom. Across the two resonance structures each of the two O atoms carries it in turn, so the real ion spreads it evenly over both - and every bond between them is identical, whatever a single drawing suggests. There are two equivalent resonance structures.
- 18 valence e−
- bent
- ≈119° bond angle
- sp2
- 1− charge
NO2− molecular geometry
Bent, from 3 electron domains on the central N: 2 bonded atoms and 1 lone pair (AX2E1). The electron geometry is trigonal planar; the shape is what is left when the lone pairs are not counted as atoms. Wedges point toward you, hashed wedges away. Every shape in the VSEPR chart →
Calculated properties
| Total valence electrons | 18 |
|---|---|
| Bonding electrons | 6 (3 shared pairs) |
| Nonbonding electrons | 12 (6 lone pairs) |
| Lone pairs on N | 1 |
| Electron domains (steric number) | 3 |
| VSEPR notation | AX2E1 |
| Electron geometry | trigonal planar |
| Molecular geometry | bent |
| Bond angle | ≈119° |
| Hybridization | sp2 |
| Charge | 1− |
| Charge distribution | delocalised over the resonance forms |
| Formal charges | O: -1 |
| Resonance structures | 2 |
| Molar mass | 46.005 g/mol |
N Nitrogen 5 valence e− O Oxygen 2 atoms, 6 valence e− each
How to draw the NO2− Lewis structure
Step through it. The bar shows how much of the 18-electron budget is spent at each stage - it never grows, which is the whole constraint.
-
Skeleton. Join every connected pair with one bond. 2 bonds spends 4 electrons.
-
Outer octets. Spend electrons as lone pairs on the outer atoms until each has eight. 2 are still unplaced.
-
Centre. Everything still unplaced goes on N, which now has 6 electrons around it.
-
Multiple bonds. The central atom is still short of an octet, so one lone pair on the outer atoms moves in to be shared. The electron count does not change - the same electrons are just counted by both atoms now.
The reasoning at each step
-
Count the valence electrons
Add up the outer-shell electrons every atom brings, then account for the charge. A 1- ion has gained one electron, so it is added to the budget. Skip this and every count that follows will be wrong.
5 (N) + 2 x 6 (O) + 1 (1- charge) = 18 valence electrons -
Choose the central atom
N is the least electronegative atom here, so it takes the centre. Hydrogen is never central: it can only form one bond.
-
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.
2 bonds x 2 = 4 electrons used, 14 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 16, has 14, 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=O2 -
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.
N: 1, O1: 3, O2: 2 (12 electrons) -
Check the central atom
N ends up with a full octet. Every electron in the budget is now placed.
N: 6 bonding + 2 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, and they are not the ion's charge either - but they must add up to it. Adding these up gives 1-, which is the check that the structure is complete.
O1: 6 - 6 - 1 = -1 -
Work out the shape
Count the electron domains on N: 2 bonded groups plus 1 lone pair. 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 bent arrangement. The lone pair takes up more room than a bonding pair, squeezing the bond angle just under the ideal 120 degrees.
steric number 3 -> sp2 -> bent, bond angle 119 -
Decide whether it is polar
The bond dipoles and lone pairs are arranged symmetrically, so the vectors cancel and the molecule has no net dipole.
dipoles cancel -> nonpolar
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 ion. NO2- is an average of the 2 structures below, which is why bonds that look different here are actually identical in the real ion.
Where the 1− charge sits
The 1− charge does not sit on one atom. Across the two resonance structures each of the two O atoms carries it in turn, so the real ion spreads it evenly over both - and every bond between them is identical, whatever a single drawing suggests.
People also ask whether NO2− is polar. Strictly it is neither: polar and nonpolar sort neutral molecules by whether their bond dipoles cancel. A 1− ion is pulled towards any nearby charge whatever its shape, which is why its salts dissolve in water regardless of geometry. The table below is still worth reading - it shows how unevenly each bond holds its electrons, which is what decides whether the charge ends up spread or concentrated.
| Bond | Electronegativity difference | Character |
|---|---|---|
| N–O | 0.40 | polar covalent |
Common questions
How many valence electrons does NO2- have?
NO2- has 18 valence electrons. The atoms bring 17 between them, and the 1− charge adds one. 6 of them are in bonds and 12 sit in lone pairs.
Why does NO2- have a 1− charge?
The 1− charge does not sit on one atom. Across the two resonance structures each of the two O atoms carries it in turn, so the real ion spreads it evenly over both - and every bond between them is identical, whatever a single drawing suggests. The brackets around the drawing are part of the answer: they say the charge belongs to the whole ion rather than to whichever atom happens to be nearest.
What is the molecular geometry of NO2-?
NO2- is a bent ion. The central N has 2 bonded groups and one lone pair, a steric number of 3, which gives trigonal planar electron geometry and a bent ion.
What is the bond angle in NO2-?
The bond angle in NO2- is 119 degrees. The lone pair takes up more room than a bonding pair, squeezing the bond angle just under the ideal 120 degrees.
What is the hybridization of NO2-?
The central N in NO2- is sp2 hybridized. Steric number 3 means 3 orbitals have to be mixed, which is exactly what sp2 gives you.
Is NO2- polar or nonpolar?
Neither, strictly. Polar and nonpolar describe neutral molecules, by asking whether their bond dipoles cancel out. NO2- carries a net 1− charge, so it is pulled towards any nearby charge whatever its shape - which is why ionic compounds dissolve in water regardless of geometry. The question the shape does answer is whether the charge is spread evenly: it is, because the bent arrangement puts every identical bond at the same angle to the others.
Does NO2- have resonance structures?
Yes. NO2- has two equivalent resonance structures. The real ion 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 ion.