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Structures and their properties
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Whether a substance melts easily, conducts electricity or is very hard depends on its structure and bonding.
Four main structures
Forms of carbon
Diamond: each carbon bonded to 4 others, very hard, does not conduct.
Graphite: layers with each carbon bonded to 3, so there are delocalised electrons; it conducts and is soft because layers slide.
Graphene: a single layer of graphite, strong and conducting.
Fullerenes: hollow balls and tubes of carbon, such as C60.
Graphite: layers with each carbon bonded to 3, so there are delocalised electrons; it conducts and is soft because layers slide.
Graphene: a single layer of graphite, strong and conducting.
Fullerenes: hollow balls and tubes of carbon, such as C60.
Simple molecules
Strong covalent bonds within molecules, but weak intermolecular forces between them. Little energy is needed to separate the molecules, so melting points are low.
Why does graphite conduct electricity but diamond does not?
- In graphite each carbon forms 3 bonds.
- The fourth electron is delocalised and can move.
- Diamond uses all 4 electrons in bonds.
Answer: Graphite has delocalised electrons.
Ionic: high melting point, conducts when molten or dissolved. Simple molecular: low melting point (weak intermolecular forces). Giant covalent: very high melting point. Metallic: conducts. Graphite conducts; diamond does not.
The interactive lesson includes the diagrams for this topic.
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