GCSE Chemistry · AQA 8462 · Topic 4.2.2
How bonding and structure are related to the properties of substances
Key points
- The three states of matter are solid, liquid and gas. Melting and freezing happen at the melting point; boiling and condensing at the boiling point. Use state symbols (s), (l), (g) and (aq).
- The simple particle model treats particles as solid spheres with no forces, which is a limitation.
- Ionic compounds have high melting and boiling points because lots of energy is needed to break the strong attractions between ions. They conduct when melted or dissolved because the ions can then move.
- Small molecules are usually gases or liquids at room temperature. The intermolecular forces between molecules are weak, and get stronger as the molecules get bigger.
- Polymers are very large molecules joined by strong covalent bonds; the larger intermolecular forces mean they are solids at room temperature.
- Giant covalent substances have very high melting points because many strong covalent bonds must be broken.
- Metals conduct because delocalised electrons carry charge; layers of atoms can slide, so pure metals are soft. Alloys are harder because different-sized atoms distort the layers.
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The properties of a substance depend on its structure and on what has to be overcome to melt, boil or conduct. This sub-topic covers states of matter and the properties of each main structure type.
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