2.3.1Bonds, Structure and Properties of Matter
Diamond structure — AQA GCSE Combined Science Trilogy 8464 - Chemistry Revision Notes & Topical Questions
5 min read 6 parts Lesson 16 of 18
Part 1 of 4Giant covalent structures
What they are
- What they are A giant covalent structure is a huge network of atoms joined by covalent bonds into a continuous lattice.
- There are no separate small molecules.
Carbon allotropes
- Carbon allotropes Carbon exists in several different forms in the same state.
- These are called allotropes and include diamond, graphite, graphene and fullerenes.
Same atoms, different structure
- Same atoms, different structure The atoms in all allotropes of carbon are identical.
- Their properties differ because the atoms are arranged and bonded differently.
Part 2 of 4Structure of diamond
1
Every carbon atom forms four strong covalent bonds to four other carbon atoms.
2
The four bonds point outwards in a tetrahedral arrangement.
3
This pattern repeats in all directions to form a rigid three-dimensional lattice.
4
All four outer electrons of each carbon are used in bonding, so none are left free to move.
Part 3 of 4Properties explained
| Property | Value | Explanation |
|---|---|---|
| Hardness | Extremely hard | Rigid lattice of strong covalent bonds in every direction, so atoms cannot slide past each other |
| Melting point | Very high (over 3500 °C) | A huge number of strong covalent bonds must be broken, requiring a lot of energy |
| Electrical conductivity | Does not conduct | No delocalised electrons or ions; all outer electrons are held in bonds |
| Solubility | Insoluble in water | The bonds are too strong for solvent molecules to separate the atoms |
| Appearance | Transparent, sparkling | The structure refracts and reflects light strongly |
Part 4 of 4Uses linked to properties
1Very hard
- Very hard Strong bonds in all directions make diamond resistant to scratching and wear.
2Cutting tools
- Cutting tools Diamond is used on the tips of drills and saws to cut other hard materials.
3Jewellery
- Jewellery Its sparkle and durability make it valuable as a gemstone.
Key terms
| Term | Meaning |
|---|---|
| Giant covalent structure | A huge network of atoms joined by covalent bonds throughout. |
| Allotropes | Different structural forms of the same element in the same physical state. |
| Tetrahedral | A shape with four bonds pointing to the corners of a tetrahedron around a central atom. |
| Covalent bond | A shared pair of electrons between two atoms. |
| Lattice | A regular repeating three-dimensional arrangement. |
Avoid these mistakes
1
Saying diamond is made of small molecules. It is a single giant covalent structure.
2
Explaining diamond's hardness by 'strong intermolecular forces'. There are none; it is the strong covalent bonds.
3
Saying diamond has delocalised electrons. All its outer electrons are used in bonds, so it does not conduct.
4
Writing that covalent bonds melt when diamond melts. Say that many strong covalent bonds must be broken.
5
Describing diamond as a different element from graphite. They are both carbon.
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