Section 1 of 6Structure of diamond
A giant covalent lattice
- A giant covalent lattice Diamond is an allotrope of carbon.
- Its atoms are joined in a huge, continuous network rather than in small separate molecules.
- Because the network has no obvious edge or fixed size, it is called a giant covalent structure.
Four bonds per atom
- Four bonds per atom Every carbon atom shares its four outer electrons to form four strong covalent bonds with four neighbouring carbon atoms.
- The four neighbours sit at the corners of a tetrahedron around the central atom, so the bonds point out in three dimensions.
A rigid three-dimensional shape
- A rigid three-dimensional shape Because the bonds spread in all directions, the whole crystal is locked into a rigid framework in which no layer or chain can move past another.
Section 2 of 6Linking structure to properties
| Property | Observation | Explanation |
|---|---|---|
| Hardness | One of the hardest natural substances | Each atom is held by four strong covalent bonds in a rigid lattice, so it is very difficult to push atoms out of position. |
| Melting point | Very high (above 3500 °C) | A huge number of strong covalent bonds must be broken, which needs a very large amount of energy. |
| Electrical conductivity | Does not conduct | All four outer electrons of each atom are used in bonds, so there are no free electrons or ions to carry charge. |
| Solubility | Insoluble in water | The solvent cannot pull atoms away from the strongly bonded lattice. |
Section 3 of 6How to explain a melting point
1
State that the substance has a giant covalent structure.
2
State that the atoms are joined by many strong covalent bonds.
3
State that a lot of energy is needed to break these bonds.
4
Conclude that the melting point is therefore very high. Do not say that molecules or intermolecular forces are broken, because diamond has no separate molecules.
Section 4 of 6Uses that follow from the properties
Diamond
Cutting and drilling
- Cutting and drilling Its extreme hardness makes diamond ideal for the tips of saws, drill bits and glass cutters,
- where it can cut materials that would blunt steel.
Jewellery
- Jewellery Pure diamond is transparent and sparkles strongly when cut, so it is prized as a gemstone.
Heat sinks and electronics
- Heat sinks and electronics Diamond is an electrical insulator but conducts heat well,
- so thin diamond layers are sometimes used to draw heat away from sensitive components.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Allotrope | One of two or more different forms of the same element in the same physical state, with different structures and properties. |
| Giant covalent structure | A huge network of atoms joined by strong covalent bonds, with no separate small molecules. |
| Covalent bond | A strong bond formed when two atoms share a pair of electrons. |
| Tetrahedral | A shape in which four atoms are arranged around a central atom, pointing to the corners of a pyramid with four triangular faces. |
| Delocalised electron | An outer electron that is not tied to one atom and is free to move; diamond has none. |
Section 6 of 6Exam technique
1
Saying diamond is hard because of strong intermolecular forces. Diamond has no molecules, so you must refer to strong covalent bonds between atoms.
2
Writing that covalent bonds melt or 'break down' when diamond is heated to its melting point without saying they are many and strong, and that a lot of energy is required.
3
Claiming that diamond conducts electricity because it contains carbon. Carbon in graphite conducts, but in diamond every outer electron is locked in a bond.
4
Drawing carbon with only three bonds in a diamond diagram. Each carbon must have exactly four bonds.