Radical
An odd electron count prevents a conventional closed-shell structure.
NO₂ is therefore paramagnetic.
Molecular radical · nitrogen oxide
Nitrogen dioxide
NO₂
Nitrogen dioxide is NO₂, a bent molecular radical with an odd number of valence electrons. One electron remains unpaired, which changes both magnetic behavior and reactivity.
Equilibrium context: NO₂ can reversibly dimerize to N₂O₄, so a gas sample can contain both species.
Essentials
NO₂ is bent and has one unpaired electron.
The dot represents an unpaired electron; the angle belongs in the detailed view, not the beginner view.
Detail
The gas-phase O–N–O angle is about 134.1°.
NIST experimental geometry gives an angle close to 134.1°, clearly bent but more open than 120°.
Odd electron
Do not force an octet-only closed-shell picture onto neutral NO₂.
The unpaired electron is part of the identity of the radical.
Understand
Two NO₂ radicals can pair to form N₂O₄.
Dimerization pairs odd electrons and forms a new N–N bond. Temperature and pressure shift the equilibrium.
Dynamic composition
A sample labeled NO₂ can contain N₂O₄.
Equilibrium composition changes with conditions.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | NO₂ |
|---|---|
| CAS Registry Number | 10102-44-0 |
| PubChem CID | 3032552 |
Advanced
Push past the first model without losing the simple picture.
Why is NO₂ a radical?
Neutral NO₂ has an odd total valence-electron count.
Is 134.1° exact?
No. It is a rounded experimental gas-phase value.
Why does dimerization occur?
Pairing the odd electrons while forming an N–N bond can stabilize the system under suitable conditions.
Constituent elements