Learning objectives
Students should be able to:
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Explain how instantaneous dipoles induce dipoles in neighbouring atoms or molecules, producing London forces.
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Describe permanent dipole–dipole attractions between polar molecules.
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Identify hydrogen-bond donors and acceptors, including the role of lone pairs.
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Identify the intermolecular forces present in a substance.
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Explain how electron-cloud polarisability and molecular contact affect London forces.
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Explain boiling in terms of overcoming intermolecular attractions while covalent bonds remain intact.
Suggested teaching sequence
1. London forces
Start with the staged explanation, pausing to identify the uneven electron distribution, instantaneous dipole and induced dipole. Move from argon to molecular examples such as chlorine, methane or carbon dioxide.
Use Fluctuate to show that dipoles continually change. The Time average view helps distinguish a molecule having no permanent dipole from it having no intermolecular attractions.
Ask students to explain the sequence using: electron distribution, instantaneous dipole, induced dipole, opposite partial charges and electrostatic attraction.
2. Permanent dipoles
Rotate the HCl molecules to compare favourable and unfavourable orientations. Ask students to identify which partial charges face one another and explain the resulting interaction.
Emphasise that polar molecules also experience London forces.
3. Hydrogen bonding
Use the molecular models and displayed formulae to identify the donor hydrogen and acceptor lone pair. Compare water with dimethyl ether.
Dimethyl ether has oxygen lone pairs but no hydrogen bonded directly to N, O or F. It therefore cannot hydrogen-bond to other dimethyl ether molecules, but it can accept hydrogen bonds from water.
4. Compare substances
Choose two substances and ask students to predict all the interactions present before revealing them. Use the displayed formulae and interaction views to connect each prediction to a specific structural feature.
Avoid treating the strongest named interaction as the only interaction present.
5. Strength and properties
Explore electron-cloud size and polarisability, then compare molecular contact in pentane and 2,2-dimethylpropane. Bring the pairs closer and change the alignment of the pentane chains to investigate how extensive contact affects total attraction.
In the boiling animation, follow the irregular liquid arrangement and rising vapour bubbles. Toggle the intermolecular contacts or track one HCl molecule to reinforce that molecules remain intact as they enter the vapour.
6. Check understanding
Use the eight questions for individual practice, paired discussion or whole-class assessment. Ask students to justify their choice before checking the explanatory feedback.
Key misconceptions and teaching points
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Electrons are not fixed dots in bonds or shells. Displayed formulae show connectivity; electron-cloud models represent electron distribution.
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Non-polar molecules still attract one another. London forces occur between all atoms and molecules.
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Inducing a dipole does not transfer electrons between molecules. It distorts the neighbouring electron distribution.
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Having hydrogen in a molecule is insufficient for hydrogen bonding. The donor hydrogen must be bonded directly to N, O or F, with a suitable lone pair on a neighbouring molecule.
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Boiling does not break covalent bonds within molecules. Energy overcomes intermolecular attractions.
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Force names alone do not determine boiling point. Molecular size, polarisability, shape and the combined interactions matter.
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Terminology varies between boards. For OCR A, London and permanent dipole–dipole interactions may both be described as van der Waals’ forces.
Display and independent use
Use Focus view or Full screen for projection. Pause, step controls and progress sliders support discussion without requiring students to follow a continuously moving animation.
For independent use, ask students to record a prediction, inspect the model and then write an explanation using A-level terminology. The tool works offline once downloaded.
The animations are slowed, qualitative models. Electron fluctuations are not regular oscillations, dashed contacts are not permanent bonds, and the boiling scene is not drawn to scale. Its sample represents pure HCl under suitable conditions, rather than hydrochloric acid in water.