💪 Very strong
Every atom in the sheet is held in place by strong covalent bonds. To tear the sheet you would have to break many of these bonds, which takes a lot of energy. So even though it is only one atom thick, graphene is very strong.
Structure and Bonding of Carbon » Graphene and Fullerenes
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.2.3.3
- What graphene is and why its structure makes it strong and a good conductor
- What fullerenes are, including Buckminsterfullerene (C60)
- What carbon nanotubes are and why they are so useful
- How to recognise graphene and fullerenes from diagrams and give their uses
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Unlock This CourseGraphene: one layer of graphite
Graphene sheets can be just one atom thick, yet they're stronger than steel
Remember, graphite is made of flat layers of hexagonal rings of carbon atoms, with weak forces between the layers. Now imagine peeling off just one of those layers. That single layer is called graphene.
Graphene is only one atom thick. It is so thin that it is often described as a two-dimensional (2D) material: it has length and width, but almost no thickness.
Key terms:
- Graphene: a single layer of graphite, one atom thick.
- Fullerene: a molecule of carbon atoms with a hollow shape.
- Carbon nanotube: a cylindrical fullerene with a very high length to diameter ratio.
Explaining the properties of graphene
The spec asks you to explain graphene's properties using its structure and bonding. In graphene, each carbon atom is covalently bonded to three other carbon atoms. This makes a flat sheet of hexagonal rings. Each carbon atom has four outer electrons, so one electron from each atom is not used in bonding. This electron is delocalised and can move across the whole sheet.
⚡ Conducts electricity
The delocalised electrons are free to move through the sheet and carry charge. This makes graphene an excellent conductor of electricity.
Graphene is also very light, because it is so thin. These properties make it useful in the two areas named in the spec:
- Electronics: it conducts electricity very well, even as an extremely thin layer.
- Composites: a small amount of graphene can be added to another material to make it stronger without making it much heavier.
Fullerenes: hollow carbon molecules
Diamond, graphite and graphene are giant structures. Fullerenes are different. They are molecules of carbon atoms with hollow shapes, such as hollow balls or hollow tubes.
The structure of fullerenes is based on hexagonal rings of carbon atoms (rings of six). But they may also contain rings with five or seven carbon atoms. These rings of five or seven let the structure bend and curve, so it can close up into a hollow shape.
Buckminsterfullerene (C60)
The first fullerene to be discovered was Buckminsterfullerene. Its formula is C60, which means each molecule is made of exactly 60 carbon atoms. It has a spherical shape, a bit like a football. In fact, the pattern of rings on C60 matches the patches on a classic football: 20 hexagons and 12 pentagons.
It was named after Buckminster Fuller, an architect who designed dome-shaped buildings with a similar pattern.
Carbon nanotubes
Carbon nanotubes help make rackets like this light but tough, so you can smash it without snapping it
Carbon nanotubes are cylindrical fullerenes. You can picture one as a sheet of graphene rolled up into a tube. They are extremely narrow but can be very long, so they have a very high length to diameter ratio. This means the tube is many, many times longer than it is wide.
Like graphene, nanotubes are held together by strong covalent bonds and have delocalised electrons. So they are very strong for their mass and they can conduct electricity. These properties make them useful for nanotechnology, electronics and materials. You will learn more about the very small scale of nanoscience in Nanoparticles and Their Properties.
Uses of fullerenes and nanotubes
💊 Delivering drugs
Fullerenes are hollow, so a drug molecule can be carried inside the cage. This makes them useful for delivering drugs into the body.
⚙ Lubricants and catalysts
Spherical C60 molecules can act as lubricants. Fullerenes also have a huge surface area for their size, so they can be used as catalysts.
🎾 Strengthening materials
Nanotubes are added to materials to reinforce them, for example in tennis rackets. Because they conduct, they are also used in electronics.
Recognising them from diagrams
You need to recognise graphene and fullerenes from diagrams and descriptions. Each diagram shows a 3D object drawn in 2D, so look for these clues:
- Graphene: one flat sheet of hexagons. Only one layer. If you see several stacked layers, it is graphite.
- Buckminsterfullerene: a closed, hollow ball of hexagons and pentagons. A formula C60 may be given.
- Carbon nanotube: a long, hollow tube with a hexagon pattern on its wall.
- Diamond: a 3D network where every carbon has four bonds, not hexagonal sheets.
Worked example
Question: A description says: 'This substance is made of carbon atoms only. It is a single layer, one atom thick. Each carbon atom is bonded to three others.' Name the substance.
Step 1: Carbon only, so it is diamond, graphite, graphene or a fullerene.
Step 2: Three bonds per carbon rules out diamond.
Step 3: It is a single flat layer, not stacked layers (graphite) or a hollow shape (fullerene).
Answer: graphene.
Worked example
Question: A diagram shows a closed, hollow cage of 60 carbon atoms arranged in hexagons and pentagons. Name it and say what type of substance it is.
Answer: Buckminsterfullerene, C60. It is a fullerene, so it is a molecule with a hollow shape, not a giant structure.
Common mistakes
Calling graphene 'a thin layer of graphite'. It is a single layer, one atom thick. Use the exact words.
Saying fullerenes are giant structures. Fullerenes are molecules with a set number of atoms, like C60.
Saying fullerenes contain only hexagons. They are based on hexagonal rings but may also have rings of five or seven carbon atoms.
Mixing up 'high length to diameter ratio'. It means the nanotube is very long compared with how wide it is, not that it is wide.
Exam-style question
(a) Graphene is used in electronics. Explain, in terms of its structure and bonding, why graphene is strong and conducts electricity. [4 marks]
(b) Give one use of fullerenes and one use of carbon nanotubes. [2 marks]
Model answer
(a) Graphene is a single layer of carbon atoms (1). Each carbon atom is joined to three others by strong covalent bonds, so a lot of energy is needed to break them, which makes it strong (1). One electron from each carbon atom is delocalised (1). The delocalised electrons can move through the structure and carry charge (1).
(b) Fullerenes: delivering drugs into the body (or lubricants, or catalysts) (1). Carbon nanotubes: reinforcing materials such as tennis rackets (or electronics) (1).
Exam tip
For any 'explain in terms of structure and bonding' question, always name the bonds (covalent), say they are strong, and for conduction say the electrons are delocalised and can move. Just writing 'electrons can move' is not enough: say the electrons are delocalised (or free) and can move through the structure.