Lesson Plan

• Describe the general form of a substitution (halogenation) reaction of alkanes.
• Explain the free‑radical mechanism (initiation, propagation, termination) for the chlorination of methane.
• Predict the products when an alkane reacts with a halogen under UV light.
• Write balanced chemical equations for substitution reactions of alkanes.
• Analyse how reaction conditions (UV light, type of halogen) influence the extent of substitution.

• Projector or interactive whiteboard
• Printed handout on alkanes and substitution reactions
• Molecular model kits (methane, haloalkane)
• Worksheet with mechanism diagrams
• Safety goggles (for UV lamp demonstration)
• UV lamp or video showing UV‑initiated halogenation

Ask students what happens to a candle flame when it is exposed to bright sunlight – the idea of light driving chemical change sparks curiosity. Recall that they already know the formulae and physical states of alkanes from previous lessons. State that by the end of the lesson they will be able to state what a substitution reaction does and identify its key steps.

1. Do‑now (5') – quick quiz on alkane formulas and physical states.
2. Mini‑lecture (10') – introduce substitution reactions, present the general halogenation equation.
3. Demonstration (10') – show a short video of UV‑driven chlorination of methane and discuss radical formation.
4. Guided practice (15') – students work in pairs to complete a worksheet that maps initiation, propagation, and termination steps.
5. Group activity (10') – each group writes and balances the equation for ethane + bromine under UV light.
6. Check for understanding (5') – exit‑ticket: one‑sentence definition of a substitution reaction.

Summarise that substitution replaces an existing atom or group with another, typically via a free‑radical chain mechanism. Collect exit‑tickets to gauge understanding and assign homework: complete the worksheet on multiple substitution and research a real‑world use of haloalkanes.