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GCSE Chemistry · key term
Forces of attraction between separate molecules.
Used by Edexcel and OCR
Specification 1.32, 6.7, 8.5 · Paper 1, Paper 2
Forces of attraction acting between separate molecules.
Revise: Classification of SubstancesWhat holds the structure together? This may be ionic, covalent or metallic bonding, or intermolecular forces between molecules.
Attractions between separate molecules that must be overcome when a molecular substance melts or boils.
Specification C6.2k · Paper 2 (Foundation), Paper 4 (Higher)
Attractive forces between separate molecules, rather than bonds between atoms within a molecule.
Revise: Distillation MechanismsLarger hydrocarbon molecules have stronger intermolecular forces between them than smaller ones. More energy is needed to separate the larger molecules from one another, so they have higher boiling points. Boiling does not break the strong covalent bonds joining carbon and hydrogen atoms within each molecule.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
Revise: Melting points of ionic compoundsMelting overcomes these weaker intermolecular forces, not the covalent bonds. Typical simple molecular substances therefore have much lower melting points than ionic compounds.
For a simple molecular substance, melting and boiling overcome intermolecular forces—not the covalent bonds within each molecule.
When explaining boiling point, refer to the energy needed to overcome intermolecular forces between molecules, not covalent bonds within a molecule.
Link molecular size to intermolecular forces, boiling point and then position in the column; do not stop at saying that fractions have different boiling points.
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