Understanding Hybridisation of NO₂: Nitrogen Dioxide

Nitrogen Dioxide (NO₂) is also known as the dioxide of nitrogen. It is a free radical with a bent shape and is reddish brown in colour. It is also a toxic gas. It’s a classic example of sp² hybridisation in inorganic chemistry.

Let us understand how hybridisation happens in NO₂. Read on to learn how it leads to its bonding and molecular shape.

What is the Hybridisation of NO₂?

Nitrogen Dioxide consists of one nitrogen atom and two oxygen atoms. Each of the oxygen atoms is bonded to the nitrogen atom. In all, the molecule also contains an unpaired electron. In order to form these bonds, nitrogen undergoes sp² hybridisation.

Breakdown of NO₂ Hybridisation

Nitrogen Dioxide’s hybridisation can be easily determined by the number of electron regions. The Lewis structure of the NO₂ also has an unpaired electron, which makes it a part of the odd-electron molecules’ family.

Here is a complete understanding of its hybridisation.

Electronic Configuration of Nitrogen

The atomic number of nitrogen is 7.

The ground state of nitrogen :

1s² 2s² 2p³

This gives nitrogen three unpaired electrons, which are enough to form two sigma bonds (with oxygen atoms) and still have one unpaired electron.

Formation of Hybrid Orbitals

sp² hybridisation occurs when 1 s orbital and 2 p orbitals mix.
The result:
→ 3 sp² hybrid orbitals on the nitrogen atom
→ The remaining 1 unhybridised p orbital stays available for π bonding

→ The one remaining electron, which is going to remain unpaired, will contribute towards the paramagnetic nature of NO₂

Bond Formation in Nitrogen Dioxide

Each nitrogen atom uses:

2 sp² orbitals to form a σ bond with oxygen
1 sp² orbital to hold the lone pair
The one unhybridised p orbital on the nitrogen atom overlaps sideways with p orbital of oxygen atom to form 1 π bond

Result:

2 N–O σ bonds
1 π bond, which is delocalised between the two N–O
1 unpaired electron on N
Hybridisation type: sp²
Bond angle: ~134° (which is due to repulsion between lone and unpaired electrons)
Geometry: Bent shape

Geometry and bonding of Nitrogen Dioxide

Details At A Glance

Property	Details

Molecule	Nitrogen Dioxide (NO₂)
Hybridisation	sp²
Geometry	Bent
Bond angle	~134°
Bonding	2 σ bonds (N–O), 1 π bond (delocalised)
Unhybridised Orbitals	1 (on nitrogen for π bonding)
Unpaired Electron	Yes (paramagnetic nature)

Formal Charge in NO₂

To determine if the Lewis structure of NO₂ is stable, we calculate the formal charge on each atom using the formula:

Formal charge = Valence electrons – (Lone pair electrons + ½ × Bonding electrons)

Step-by-step for each atom:

Nitrogen (N) – central atom

Valence electrons: 5
Lone pairs: 1
Bonding electrons: 6
(4 from double bond with one O, 2 from one single bond with the other O)

Formal charge = 5 – (2 + ½×6) = 5 – (2 + 3) = 0

Oxygen (O) – doubly-bonded

Valence electrons: 6
Lone pairs: 2
Bonding electrons: 4
(1 double bond with nitrogen)

Formal charge = 6 – (4 + ½×4) = 6 – (4 + 2) = 0

Oxygen (O) – singly-bonded

Valence electrons: 6
Lone pairs: 3
Bonding electrons: 2
(1 single bond with nitrogen)

Formal charge = 6 – (6 + ½×2) = 6 – (6 + 1) = –1

Thus, atoms in NO₂ carry formal charge of Nitrogen (0), Doubly-bonded oxygen (0) and singly bonded oxygen (-1), and since the molecule has resonance hybrid the negative charge is then delocalised over both atoms of oxygen.

Summing Up

The nitrogen in NO₂ forms 2 bonds with oxygen and shares a π bond (delocalised) with the same atoms. sp² hybridisation leads to a bent shape and slightly greater than 120° in ideal sp², but in NO₂ it is actually ~134°. The change in bond angle is because of the repulsion between unpaired and lone pair electrons.

Frequently Asked Questions

Q1. How many σ and π bonds are present in NO₂?

There are 2 σ bonds and 1 π (delocalised) bond in total.

Q2. Is NO₂ polar or non-polar?

Nitrogen dioxide is polar. The molecule has a bent shape and a significant electronegativity difference between nitrogen and oxygen. Thus, it creates a net dipole moment.

Q3. What is the shape of NO₂?

Bent, due to repulsion between lone pair and unpaired electrons.