Simple Covalent Molecules
Chemistry: Cambridge International A Level, topic 1.4.1
Intermolecular Forces and Molecule Structure
The size of a molecule affects the overall strength of intermolecular forces. The strength of intermolecular forces affects the properties of a molecule.
Small molecules
- Small molecules have weak intermolecular forces. This means that they have low melting and boiling points.
- Because of this, they are often liquids or gases at room temperature.
- Small molecules don't contain delocalised electrons. Because of this, they cannot conduct electricity.
Chlorine - example of a small molecule
- Cl2 (the diatomic molecule of chlorine) is a small molecule with weak intermolecular forces between its molecules.
- It is a gas at room temperature.
Bigger molecules
- Bigger molecules attract other molecules with stronger intermolecular forces. This means that they have higher melting and boiling points than small molecules.
- Don't contain delocalised electrons, and so can't conduct electricity.
Sucrose - example of a bigger molecule
- Sucrose is made of 45 atoms and has the formula C12H22O11.
- Although it is a simple molecule, its size means that its intermolecular forces are strong enough for it to be solid at room temperature.
Test yourself on Simple Covalent Molecules
Why are small covalent molecules liquids or gases at room temperature?
How would you describe the intramolecular bonds and intermolecular forces associated with small molecules?
Which molecule has higher melting and boiling points?
Why is chlorine a gas at room temperature?
Why do bigger molecules have stronger overall intermolecular forces than smaller molecules?