AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
In graphite, each carbon atom forms three covalent bonds with three other…
Full specification wording
Graphite: In graphite, each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers.
Graphite is a giant covalent structure of carbon, but each carbon atom bonds covalently to only three others, producing flat layers of hexagonal rings.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 1 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Graphite is a giant covalent structure of carbon, but each carbon atom bonds covalently to only three others, producing flat layers of hexagonal rings. The fourth outer electron per atom is delocalised and can move along the layer, so graphite conducts electricity. Within a layer, the strong covalent bonds need a great deal of energy to break, giving graphite a very high melting point. Between layers there are no covalent bonds, only weak forces, so layers can slide over one another; this makes graphite soft and slippery, suitable for pencil leads and as a lubricant. A useful method is to separate the two length scales: strong covalent bonding within each layer, weak forces between layers.
What earns the marks
- Each carbon atom in graphite forms three covalent bonds with three other carbon atoms, leaving one outer electron delocalised.
- The bonded atoms form layers of hexagonal rings, and each layer is a giant covalent structure.
- There are no covalent bonds between the layers; only weak forces act between them, so the layers can slide over one another.
- The strong covalent bonds within a layer require much energy to break, so graphite has a very high melting point.
- The delocalised electrons can move along the layers, so graphite conducts electricity.
- The weak forces between layers explain why graphite is soft and slippery, unlike diamond.
Common mistakes and how to put them right
Saying graphite is a simple molecular substance.
Put it right by describing it as a giant covalent structure made of layers of hexagonal rings.
Stating that graphite melts easily because layers slide.
Put it right by distinguishing weak forces between layers from the strong covalent bonds within layers, which give a very high melting point.
Claiming graphite conducts because of covalent bonds.
Put it right by explaining that delocalised electrons, not the bonds themselves, carry charge.
Exam tips
- Always distinguish within-layer covalent bonding from between-layer forces, since this contrast explains both the high melting point and the softness.
- When explaining conduction, name delocalised electrons explicitly and say they can move along the layers.
- Use a labelled diagram of hexagonal layers if it helps, but keep the written explanation of bonding and forces clear.
Try the lesson
The start of the Graphite: In graphite, each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers. lesson, made from checked teaching notes for this specification point.
Have a go first
How many covalent bonds does each carbon atom form in graphite?
Listen
Graphite is a giant covalent structure of carbon, but each carbon atom bonds covalently to only three others, producing flat layers of hexagonal rings. The fourth outer electron per atom is delocalised and can move along the layer, so graphite conducts electricity. Within a layer, the strong covalent bonds need a great deal of energy to break, giving graphite a very high melting point. Between layers there are no covalent bonds, only weak forces, so layers can slide over one another; this makes graphite soft and slippery, suitable for pencil leads and as a lubricant. A useful method is to separate the two length scales: strong covalent bonding within each layer, weak forces between layers. A strong answer earns marks for these points. Each carbon atom in graphite forms three covalent bonds with three other carbon atoms, leaving one outer electron delocalised. The bonded atoms form layers of hexagonal rings, and each layer is a giant covalent structure. There are no covalent bonds between the layers; only weak forces act between them, so the layers can slide over one another. The strong covalent bonds within a layer require much energy to break, so graphite has a very high melting point. A common slip: Saying graphite is a simple molecular substance. Instead, describing it as a giant covalent structure made of layers of hexagonal rings. Exam tip: Always distinguish within-layer covalent bonding from between-layer forces, since this contrast explains both the high melting point and the softness.
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Key words
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Giant covalent structures
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Covalent bonding and delocalised electrons
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Structure-property relationships
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Electrical conductivity in materials
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See every definition
- Giant covalent structures
- Graphite is a giant covalent structure of carbon, and each layer is a giant covalent structure.
- Covalent bonding and delocalised electrons
- Each carbon atom forms three covalent bonds with three other carbon atoms, leaving one outer electron delocalised.
- Structure-property relationships
- Strong covalent bonds within a layer need much energy to break, while weak forces between layers let them slide, so graphite has a very high melting point but is soft and slippery.
- Electrical conductivity in materials
- The delocalised electrons can move along the layers, so graphite conducts electricity.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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