Diamond and graphite (AQA GCSE Chemistry): Revision Notes
Diamond and graphite
What are giant covalent structures?
Some substances are made up of huge networks of atoms all joined together by covalent bonds. These are called giant covalent structures. The atoms form a pattern called a lattice.
Carbon can form two different giant covalent structures - diamond and graphite. Both are made from the same element (carbon) but have completely different properties!
The key to understanding diamond and graphite is recognising that even though they're both made of carbon atoms, their different arrangements in space create completely different materials with unique properties.
Diamond structure and properties
How diamond is structured
- Carbon atoms in diamond form a 3D lattice structure
- Each carbon atom bonds to four other carbon atoms
- All bonds are strong covalent bonds
- This creates a very strong, rigid structure
Properties of diamond
- Very hard - used in cutting tools and drill bits
- Very high melting point - because lots of strong covalent bonds need breaking
- Does not conduct electricity - all electrons are used in bonding, so none are free to move
Diamond's incredible hardness comes from its structure: each carbon atom is locked in place by four strong covalent bonds arranged in a tetrahedral shape, creating a rigid 3D network that's extremely difficult to break.
Graphite structure and properties
How graphite is structured
- Carbon atoms in graphite form layers
- Each carbon atom bonds to three other carbon atoms in the same layer
- Weak forces exist between the different layers
- One electron from each carbon atom is delocalised (free to move around)
Properties of graphite
- Soft and slippery - layers can slide over each other easily due to weak forces between them
- Very high melting point - strong covalent bonds within each layer need breaking
- Conducts electricity - delocalised electrons can move and carry electrical charge
- Used in pencils and as a lubricant
Graphite's layered structure is the key to understanding its properties. Within each layer, carbon atoms are strongly bonded, but the layers themselves are only held together by weak intermolecular forces.
Why do diamond and graphite have different properties?
Even though both are made from carbon atoms, their different structures give them different properties:
- Diamond is hard because each carbon is held rigidly in place by four strong bonds
- Graphite is soft because the layers can slide over each other due to weak forces between them
- Diamond doesn't conduct because all electrons are trapped in bonds
- Graphite conducts because it has free electrons that can move between layers
Structure determines properties! The way atoms are arranged in a substance directly controls how that substance behaves. This is a fundamental principle in chemistry and materials science.
Key Points to Remember:
- Diamond and graphite are both giant covalent structures made from carbon atoms
- Diamond: 4 bonds per carbon → hard, doesn't conduct electricity
- Graphite: 3 bonds per carbon → soft, conducts electricity due to delocalised electrons
- Both have very high melting points because of strong covalent bonds
- Their different structures explain their different properties