Graphite structure

Section 1 of 6Structure of graphite

1

Each carbon atom is joined by strong covalent bonds to three other carbon atoms.

2

The atoms form flat layers of hexagonal rings, which can be pictured as sheets of chicken wire.

3

Because each carbon uses only three of its four outer electrons for bonding, one electron per atom is left over.

4

These spare electrons become delocalised and are free to move between and along the layers.

5

The layers are held to each other only by weak intermolecular forces, with a gap between them.

Section 2 of 6Properties explained

Property	Explanation
Very high melting point	Strong covalent bonds within each layer must be broken, which takes a lot of energy
Soft and slippery	Weak forces between layers allow them to slide over each other
Conducts electricity	Delocalised electrons carry charge through the structure
Conducts heat	The delocalised electrons transfer thermal energy
Insoluble in water	The strong bonding in the layers cannot be broken by solvent molecules
Low density for a solid	The layers are relatively far apart

Section 3 of 6Comparison with diamond

Bonds per carbon

• Bonds per carbon Diamond has four covalent bonds per carbon atom; graphite has three.

Structure

• Structure Diamond is a rigid 3D lattice; graphite is arranged in layers.

Electrons

• Electrons Diamond has no free electrons; graphite has one delocalised electron per atom.

Hardness

• Hardness Diamond is extremely hard; graphite is soft and flaky.

Section 4 of 6Uses

Graphite

Lubricant

• Lubricant The layers slide easily, so graphite reduces friction between moving parts.

Electrodes

• Electrodes Its conductivity and high melting point make it suitable for electrodes in electrolysis.

Pencils

• Pencils Layers rub off onto paper, leaving a grey mark.

Section 5 of 6Key terms

Term	Meaning
Graphite	An allotrope of carbon in which atoms form flat layers of hexagonal rings.
Delocalised electron	An electron that is free to move through a structure and is not fixed to one atom.
Hexagonal	Having six sides, as in the rings of carbon atoms.
Layer	A single flat sheet of bonded atoms.
Electrode	A conductor through which current enters or leaves an electrolyte.

Section 6 of 6Exam technique

1

Saying graphite is soft because covalent bonds are weak. The bonds in the layers are strong; it is the forces between layers that are weak.

2

Stating that graphite has four bonds per carbon. It has three.

3

Forgetting why it conductsone electron from each carbon is delocalised.

4

Claiming that graphite has a low melting point because it is soft. Its melting point is very high.

5

Describing the layers as bonded by covalent bonds to each other. Only weak intermolecular forces connect them.