Understanding Hybridisation of Graphite: Allotrope of Carbon

Graphite is also known as plumbago or black lead. It is an allotrope of carbon and has hexagonal ring layers which contain carbon atoms, which are bonded covalently with 3 other carbons. It’s an excellent example of sp² hybridisation in carbon chemistry.

Let us understand how hybridisation happens in Graphite. Read on to learn how it leads to its bonding, unique shape and also how it affects its conductivity.

What is Hybridisation in Graphite?

Each carbon in graphite consists of 3 sigma bonds. The carbon atom is bonded to 2 neighbouring carbons and one other carbon of the same hexagonal layer. In order to form these bonds, carbon undergoes sp² hybridisation.

Breakdown of Graphite Hybridisation

Graphite consists of carbon layers which are linked to each other with weak van der Waals forces. This layer is generally called graphene.

Here is a complete understanding of its hybridisation.

Electronic Configuration of Carbon

The atomic number of carbon is 6.

The ground state of carbon :

1s² 2s² 2p²

Only two unpaired electrons → insufficient to form 3 bonds and delocalised bond

Excited state configuration:

formula

Four unpaired electrons → enough to form 3 bonds and leaves with 1 π electron

Ground state vs excited state orbital diagram of carbon

Formation of Hybrid Orbitals

sp² hybridisation occurs when 1 s orbital and 2 p orbitals mix.
The result:
→ 3 sp² hybrid orbitals per carbon atom in a plane
→ The remaining one unhybridised p orbital ( 2p) stays available for π bonding (which will be delocalised), and perpendicular to the plane

Bond Formation in Graphite

Each carbon uses:

3 sp² orbitals to form a σ bond with adjacent carbons
The one unhybridized p orbitals on each carbon atom overlap sideways to form π cloud instead of a bond; it is also delocalised.

Result:

The C-C σ bond and partial π bond are present in every carbon atom of the layer
Electrical conductivity is also present along the plane due to the delocalisation of π electrons
Hybridisation type: sp²
Bond angle: 120°
Geometry: Trigonal planar (on every carbon)

Geometry of graphite and bonding in graphene

Details At A Glance

Property	Details
Molecule	Graphite (C)
Hybridisation	sp²
Geometry	Trigonal planar
Bond angle	120°
Bonding	3 σ bonds ( C–C), 1 delocalised π cloud
Unhybridised Orbitals	1 (on each carbon)
Carbon valency satisfied?	Yes, by forming 3 bonds on each carbon and pi delocalisation

Formal Charge in Graphite

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

Step-by-step for each atom:

Carbon (C) – each

Valence electrons: 4
Lone pairs: 0
Bonding electrons: 6
( 6 electrons from sigma bond with other C)

Formal charge = 4 – (0 + ½×6) = 4 – 3 = +1

Graphite does have +1 formal charge, but the delocalisation of π electrons will be evenly distributed, which would in turn make the effective formal charge 0.

Summing Up

Each carbon in Graphite forms 3 bonds: all with another carbon in the layer. sp² hybridisation leads to high electrical conductivity in the molecule, and the bond angle of 120° results in a layered structure. The atoms also partake in a delocalised π network.

Frequently Asked Questions

Q1. Why does carbon undergo hybridisation in graphite?

To form 3 sigma bonds (which are present in the same plane), carbon promotes an electron and mixes orbitals to form hybrid orbitals. This allows one unhybridised p orbital to undergo π delocalisation.

Q2. How many σ and π bonds are present in graphite?

There are 3 σ bonds and π delocalisation clouds.

Q3. What is the shape of carbon atoms in graphite?

The carbon atoms have trigonal planar geometry.

Q4. Is Graphite a good conductor?

The one left unhybridised valence electron undergoes delocalised pi bonding in order to avoid being confined to certain pairs of carbon atoms, and because of the property, graphite is a good conductor.

Q5. What are some uses of graphite in our lives?

Graphite is commercially, widely used in pencil leads and electrodes. It also has important usage in nuclear reactors as moderators. It is also widely used in lubricants.