Diamond, Graphite and Graphene
Recap Diamond, Graphite and Graphene for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Diamond is hard with four bonds per carbon, while graphite conducts because each carbon forms three bonds, leaving one delocalised electron.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Diamond, graphite and graphene are all forms of carbon, but their very different properties come entirely from how the carbon atoms are bonded.
In diamond each carbon atom forms four covalent bonds in a rigid giant structure, making it very hard with a very high melting point, and it does not conduct electricity because no electrons are free.
In graphite each carbon atom forms only three bonds, creating layers of hexagonal rings with no bonds between the layers. The layers can slide, making graphite soft and slippery, and the fourth electron per atom is delocalised so graphite conducts electricity. Graphene is a single layer of graphite, one atom thick.
Revision notes
Diamond
Each carbon atom forms four covalent bonds in a giant rigid three-dimensional structure.
It is very hard and has a very high melting point because many strong covalent bonds must be broken. It does not conduct electricity because all four outer electrons are used in bonding.
Graphite
Each carbon atom forms only three covalent bonds, producing layers of hexagonal rings.
There are no covalent bonds between the layers, only weak intermolecular forces, so the layers can slide over each other — making graphite soft and slippery, and useful as a lubricant. The fourth electron of each atom is delocalised.
Graphene
Graphene is a single layer of graphite, just one atom thick.
It is extremely strong because of its covalent bonds, and it conducts electricity because of its delocalised electrons. Its properties make it useful in electronics and composites.
Key points
- Diamond has four covalent bonds per carbon atom.
- Diamond is hard and does not conduct electricity.
- Graphite has three covalent bonds per carbon atom.
- Graphite has layers with no bonds between them.
- Graphite conducts because of delocalised electrons.
- Graphene is a single layer of graphite.
Worked examples
Example 1
Explain why graphite is soft and slippery but diamond is very hard. [4 marks]
Model answer
In graphite the carbon atoms form layers with no covalent bonds between the layers (1 mark), so the layers can slide over each other easily, making it soft and slippery (1 mark). In diamond each carbon atom forms four covalent bonds in a rigid three-dimensional structure (1 mark), so there are no layers to slide and the structure is very hard (1 mark).
Example 2
Explain why graphite conducts electricity but diamond does not. [3 marks]
Model answer
In graphite each carbon atom forms only three covalent bonds (1 mark), so one electron per atom is delocalised and free to move, carrying charge (1 mark). In diamond all four outer electrons of each carbon atom are used in bonding, so none are free to move (1 mark).
Example 3
State what graphene is. [2 marks]
Model answer
Graphene is a single layer of graphite (1 mark), just one atom thick (1 mark).
Common mistakes
Saying graphite is soft because its bonds are weak.
The covalent bonds are strong; it is the absence of bonds BETWEEN layers that allows sliding.
Saying diamond conducts electricity.
It does not, because all four outer electrons are used in bonding.
Giving graphite four bonds per atom.
Graphite has three, leaving one electron delocalised.
Saying graphene is a form of diamond.
It is a single layer of graphite.
Exam tips
- Learn the number of bonds per carbon atom for each form.
- Explain graphite's softness through no bonds between layers.
- Link conductivity to the fourth delocalised electron.
- Compare diamond and graphite directly when asked.
Key terms
- Diamond
- A giant covalent form of carbon with four bonds per atom.
- Graphite
- A layered form of carbon with three bonds per atom.
- Graphene
- A single layer of graphite, one atom thick.
- Lubricant
- A substance reducing friction, such as graphite.
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Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.