Graphene (Higher Tier)

Structure of Graphene

Graphene is a single layer of carbon atoms arranged in a two-dimensional hexagonal lattice. Each carbon atom forms strong covalent bonds with three other carbon atoms, creating a flat sheet of hexagons.

Because each carbon atom is bonded to three others, there is one electron from each carbon atom that is not involved in bonding. These electrons become delocalised, meaning they are free to move across the whole sheet of graphene.

This delocalisation of electrons is crucial for graphene’s unique properties. The hexagonal pattern repeats indefinitely, giving graphene a giant covalent structure but only one atom thick.

For instance, the hexagonal lattice means each carbon atom has a bond angle of 120°, typical of trigonal planar geometry, which contributes to the flatness and stability of the sheet.

Properties of Graphene

Graphene has remarkable properties due to its structure:

• Excellent electrical conductor: The delocalised electrons can move freely across the sheet, allowing graphene to conduct electricity very efficiently.
• Very strong and lightweight: The strong covalent bonds between carbon atoms make graphene one of the strongest known materials, yet it is incredibly light because it is only one atom thick.
• High thermal conductivity: Graphene can transfer heat quickly, making it useful in applications where heat dissipation is important.
• Flexible and nearly transparent: Despite its strength, graphene is flexible and almost completely transparent, absorbing only about 2% of visible light.

These properties make graphene very different from other forms of carbon like diamond or graphite, which have different bonding and structures (see separate notes on these).

For example, graphene’s electrical conductivity is much higher than copper, a common metal conductor, because electrons can move with less resistance through the delocalised network.

Uses of Graphene

Graphene’s unique combination of properties has led to many exciting potential uses:

• Electronics and sensors: Its high conductivity and thinness make graphene ideal for developing tiny, sensitive electronic devices and sensors.
• Composite materials: Adding graphene to plastics or metals can create composites that are stronger, lighter, and more conductive.
• Energy storage devices: Graphene is used in batteries and supercapacitors to improve charge speed and capacity.
• Flexible displays: Because it is flexible and transparent, graphene could be used in bendable screens for phones and other devices.

Learning Example: Calculating Bond Angles in Graphene

Each carbon atom in graphene forms three covalent bonds arranged in a flat hexagonal pattern. The shape around each carbon atom is trigonal planar, so the bond angles are approximately 120°.

This can be understood because the three bonding pairs of electrons repel each other equally, spreading out evenly in a plane to minimise repulsion.

Therefore, the bond angle in graphene is:

$\text{Bond angle} = 120^\circ$