Simple molecular structures (Edexcel GCSE Chemistry Combined Science): Revision Notes
Simple molecular structures
Simple molecular structure: A substance composed of millions of individual small molecules that are weakly attracted to other molecules through intermolecular forces.
Intermolecular Forces: These are the weak attractions between molecules that keep them together but are much weaker than the covalent bonds within the molecules.
Examples:
- Hydrogen (H₂): A simple molecule with two hydrogen atoms bonded together.
- Water (H₂O): A small molecule with two hydrogen atoms and one oxygen atom.
Properties of Simple Molecular Structures
1. Low Melting and Boiling Points
The intermolecular forces between molecules are weak, meaning they require little energy to break. As a result, substances with simple molecular structures are often gases or liquids at room temperature.
Examples:
- Water (H₂O) melts at 0°C and boils at 100°C.
- Oxygen (O₂) boils at -183°C.
2. Volatile
A volatile substance changes state (from liquid to gas) easily. This is because the intermolecular forces are weak, and molecules can escape into the gas phase quickly.
- This property is why many simple molecular substances have strong smells (e.g., perfumes).
3. Do Not Conduct Electricity
Simple molecular substances lack free electrons or charged particles (ions) that can move and carry an electric current. In these structures, all electrons are used in forming covalent bonds, so there are no free electrons available to move and conduct electricity.
Examples:
- Water (H₂O) does not conduct electricity in its pure form.
- Carbon dioxide (CO₂) is another example that cannot conduct electricity. | Property | Explanation | Examples | |---|---|---| | Low melting and boiling point | Weak intermolecular forces require little energy to break | H₂, CO₂, H₂O | | Volatile | Weak intermolecular forces allow easy transition to gas | Perfumes, acetone | | Do not conduct electricity | No free-moving electrons or charged particles | H₂O (pure), O₂, CH₄ |