Diamond, graphite and giant structures Cambridge IGCSE Co-ordinated Sciences (9–1) revision
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In plain words
Sometimes covalent bonds don't stop at a small molecule: they carry on in every direction, joining billions of atoms into one giant structure. Diamond and graphite are both pure carbon built this way. They are so different because the atoms are joined in different patterns.
Three things to know
- Diamond: each carbon atom is joined to four others in a giant structure. Very hard, very high melting point, does not conduct electricity.
- Graphite: each carbon atom is joined to three others, in layers. The layers slide (soft, a lubricant) and the spare electrons are free to move (conducts electricity).
- Silicon dioxide (silicon(IV) oxide, sand) has a giant structure like diamond's, so it is hard with a high melting point.
Tips and tricks
- Diamond: 4 bonds per atom, no free electrons, hard. Graphite: 3 bonds per atom, one free electron per atom, in layers that slide.
- High melting point "because many strong covalent bonds must be broken". Not forces between molecules: there are no molecules.
It lands in your notebook with its questions as flashcards.
Diamond, graphite and giant structures: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
How many other carbon atoms is each carbon atom bonded to in diamond?
All four outer electrons are used in covalent bonds.
Why does graphite conduct electricity?
Each carbon atom has one electron not used in bonding.
Why does diamond have a very high melting point?
It is one giant structure, not separate molecules.
Which substance has a giant covalent structure?
Its atoms are joined in a network like diamond's.
Why is graphite soft and slippery?
The forces between the layers are weak.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Diamond, graphite and giant structures
Cambridge IGCSE Co-ordinated Sciences (9–1) 0973 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Explain why graphite conducts electricity but diamond does not.[3]
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In graphite each carbon uses only three of its four outer electrons for bonding, so one electron per atom is free to move. In diamond all four are used in bonds, so none are free.
Explain why diamond is used on cutting tools.[2]
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It is very hard, because every atom is held by four strong covalent bonds in a rigid giant structure.
Explain why graphite is used as a lubricant.[2]
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Its layers are held together only by weak forces, so they slide over each other easily.
Answers: Diamond, graphite and giant structures
- 1. In graphite each carbon uses only three of its four outer electrons for bonding, so one electron per atom is free to move. In diamond all four are used in bonds, so none are free.
- 2. It is very hard, because every atom is held by four strong covalent bonds in a rigid giant structure.
- 3. Its layers are held together only by weak forces, so they slide over each other easily.