This PowerPoint lesson covers Boiling Points and Intermolecular Forces for Pearson BTEC Applied Science Unit 5 Chemistry, including London dispersion forces, chain length, molecular size and branching. It is designed to help students explain trends in the boiling points of hydrocarbons and structural isomers using intermolecular forces.
An intermolecular force is an attractive force between separate molecules. The lesson distinguishes these attractions from the covalent bonds within molecules and explains that boiling involves overcoming intermolecular forces rather than breaking covalent bonds. Students learn that hydrocarbons are held together by relatively weak London dispersion forces, helping to explain their comparatively low melting and boiling points.
The resource develops the relationship between carbon-chain length and boiling point, showing how larger hydrocarbon molecules contain more electrons and experience stronger London forces. Students apply this trend to both alkanes and alkenes. The lesson then explores the effect of branching, explaining why more highly branched structural isomers are more compact, have less effective surface contact with neighbouring molecules and therefore usually have lower boiling points than less-branched isomers. Examples using pentane, 2-methylbutane and 2,2-dimethylpropane help students apply these ideas to real boiling-point comparisons.
The fully editable PowerPoint (.pptx) includes learning objectives, key terminology, a retrieval starter, structured explanations, worked exam-style answers, data and comparison activities, answer slides and end-of-lesson check-your-understanding questions. Updated in October 2026, it is suitable for classroom teaching, revision, cover work or independent study within Pearson BTEC Applied Science Unit 5 Chemistry.
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