Explicit science instruction
Electron density fluctuates continuously. Temporary uneven distributions can induce neighboring dipoles, producing London dispersion attraction even in nonpolar substances.
Dispersion generally grows as electron clouds become larger and more polarizable. Shape also matters because extended contact can increase interaction opportunities.
Dispersion is present in polar molecules too; stronger named interactions are added to it rather than replacing it.
Vocabulary: dispersion force; instantaneous dipole; induced dipole; polarizability; contact area.
Worked example with reasoning
Within a homologous series, larger molecules often boil at higher temperatures because their larger electron clouds are more polarizable and support stronger dispersion attraction.
Guided question
Why can two nonpolar molecules have very different boiling points? Give two structural factors that can matter.
Independent work
- Rank three nonpolar molecules by expected dispersion strength using size data.
- Explain how shape can affect intermolecular contact.
- State one reason molecular mass alone is an incomplete predictor.
Misconception check
Nonpolar does not mean 'no intermolecular attraction.'
Formative understanding check
Do noble-gas atoms experience intermolecular attraction?
Reveal response
Yes. Temporary dipoles produce dispersion forces even in monatomic species.
Mentor evidence conference
Ask Archaemenes to test whether your structure–property claim controls competing variables.
Teacher guidance
Foundation: Use size to rank simple cases.
Core: Integrate size and shape into dispersion predictions.
Extended: Evaluate a case where mass and shape predict competing effects.