Properties of small molecules — AQA GCSE Chemistry
Test yourself on Properties of small molecules with AQA GCSE practice questions.
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Properties of small molecules explained
Simple molecular substances do not conduct electricity in any state because their molecules are neutral overall.
Read the full explanation
A molecule such as methane (CH₄) contains covalent bonds, but the shared electrons are held between the atoms and are not free to move through the substance. There are no charged particles, such as ions or delocalised electrons, that can carry charge. Even though individual atoms in a bond may carry small partial charges, the molecule as a whole has no overall electric charge. This is why substances like water, carbon dioxide and iodine do not conduct electricity, unlike ionic compounds when molten or dissolved, or metals and graphite which contain delocalised electrons.
Your focus
- State why simple molecular substances do not conduct electricity.
- Identify the charged particles needed for electrical conduction.
- Compare simple molecular substances with ionic and metallic conductors.
Properties of small molecules exam tips
Marking Points
- Simple molecular substances contain neutral molecules with no overall charge.
- There are no free ions or delocalised electrons to carry charge.
- Covalent bonds hold atoms together within molecules but do not provide mobile charge carriers.
- Conduction requires charged particles that are free to move.
- This explains why simple molecular substances do not conduct electricity in the solid, liquid or gaseous state.
Examiner Tips
- 💡Refer explicitly to the absence of free ions or delocalised electrons as the reason for no conduction.
- 💡Avoid saying molecules have no charge at all; state that they have no overall electric charge.
- 💡Contrast with a conducting substance, such as a molten ionic compound, to show understanding.
Common Mistakes
- Thinking that covalent bonds allow conduction because electrons are shared; the correction is that shared electrons are localised and not free to move through the substance.
- Confusing simple molecular substances with ionic compounds; the correction is that ionic compounds conduct when molten or dissolved because their ions are free to move.
- Believing that all non-metals cannot conduct; the correction is that graphite, a non-metal, conducts because it has delocalised electrons.