3.7 - Giant covalent structures

Question 1

What is an allotrope

Answer 1

The different structural forms of an element in the same state

Question 2

Bonding and structure of graphite

Answer 2

• Each carbon atom forms 3 strong covalent bonds in a planar hexagonal pattern, with each carbon contributing 1 delocalised electron.
• Multiple stacked layers of hexagonal carbon arrays with weak intermolecular forces between layers.

Question 3

Giant covalent structure

Answer 3

• extensive interconnecting networks of covalently bonded atoms
• has a huge lattice

Question 4

Properties of diamond (5)

Answer 4

• Extremely hard- Extensive network of strong covalent bonds not easily broken.
• Very high melting point- Huge amount of energy needed to break enough bonds to melt diamond.
• Good thermal conductor- Strong interatomic bonds transmit heat through vibrations.
• Electrical insulator- All outer electrons tied up in localised bonds so no free electrons to carry charge.
• Insoluble - Covalent bonds too strong to be broken by solvation.

Question 5

Diamond bonding and structure

Answer 5

• Each carbon atom forms 4 very strong covalent bonds with others in a tetrahedral arrangement.

Question 6

Properties of graphite (4)

Answer 6

• Soft and slippery- Weak intermolecular forces let sheets slide over each other.
• Conducts electricity along layers- Delocalised electrons move through the 2D lattice carrying electrical charge.
• Lower density than diamond- Weak intermolecular forces lead to increased separation between layers.
• High sublimation temperature but lower melting point than diamond - Covalent bonds within each layer are very strong but the weaker intermolecular forces between layers means graphite melts at a lower temperature.