Intermolecular
Forces
This section covers the forces between molecules: permanent dipole-dipole forces, induced dipole-dipole forces and hydrogen bonding. It also links the strength of these intermolecular forces to melting points, boiling points, ice and anomalous boiling points.
Revision Notes
Work through the three intermolecular forces in sequence.
Forces
London Forces
Induced dipole-dipole forces, also called van der Waals, dispersion or London forces, and what sets their strength.
Start revisingForces
Permanent Dipole-Dipole Forces
Attractions between molecules with permanent dipoles, and deciding the forces in an unfamiliar molecule.
Start revisingBonding
Hydrogen Bonding
The N-H, O-H and H-F requirement, the exam diagram, and predicting hydrogen bonding in other molecules.
Start revisingWater
Anomalous Properties of Water
Why water boils at 100 °C, why ice floats and why water has a high surface tension.
Start revisingTrends
Boiling Point Trends
Alkane chain length and branching, alcohols against alkanes, and the hydrogen halides.
Start revisingSolvents
Choosing Solvents
Hydration of ions, alcohols in water, halogenoalkanes and non-aqueous solvents.
Start revisingIntermolecular Forces – AQA A Level Chemistry
The following AQA specification point outlines the knowledge and skills students are expected to demonstrate for intermolecular forces.
Forces between molecules:
– permanent dipole-dipole forces
– induced dipole-dipole (van der Waals, dispersion, London) forces
– hydrogen bonding.
The melting and boiling points of molecular substances are influenced by the strength of these intermolecular forces.
The importance of hydrogen bonding in the low density of ice and the anomalous boiling points of compounds.
Students should be able to:
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