| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Chemistry |
| Lesson Topic: Describe the Group VII halogens, chlorine, bromine and iodine, as diatomic non-metals with general trends down the group, limited to: (a) increasing density (b) decreasing reactivity |
Learning Objective/s:
- Describe the diatomic nature and physical states of chlorine, bromine, and iodine.
- Explain why density increases down Group VII.
- Explain why reactivity decreases down Group VII.
- Compare the three halogens using density and reactivity data and infer laboratory handling implications.
- Apply the trends to solve a short problem or predict the safest halogen for a given experiment.
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Materials Needed:
- Projector or interactive whiteboard
- Printed handout with the comparative data table
- Periodic table poster
- Images or short video clips of Cl₂ gas, Br₂ liquid, I₂ solid
- Group worksheet activity sheets
- Exit‑ticket slips
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Introduction:
Begin with a quick visual of the three halogens to spark curiosity about why they look so different. Ask students what they already know about diatomic gases and liquids. State that by the end of the lesson they will be able to describe the trends in density and reactivity down the group and explain the underlying reasons.
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Lesson Structure:
- Do‑now (5 min): Short quiz on halogen symbols, atomic numbers, and physical states.
- Mini‑lecture (10 min): Review diatomic nature, show the comparative data table, introduce the two trends (density ↑, reactivity ↓).
- Guided inquiry (12 min): In pairs, students plot density vs. element and discuss why the trend occurs, referencing atomic radius and van der Waals forces.
- Demonstration/video (8 min): Safe handling of Cl₂ gas, Br₂ liquid, and I₂ solid, linking observations to reactivity differences.
- Check for understanding (5 min): Whole‑class “thumbs up/down” on statements about the trends.
- Worksheet activity (10 min): Apply concepts to answer questions and draft a brief lab‑safety recommendation for each halogen.
- Exit ticket (5 min): Write one sentence summarising why density increases and reactivity decreases down Group VII.
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Conclusion:
Recap the key reasons for the increasing density (larger atoms, stronger intermolecular forces) and decreasing reactivity (lower electron affinity, greater shielding). Collect exit tickets to gauge understanding and assign a short homework task: students create a labelled diagram of Group VII showing the trends and annotate it with the explanations discussed.
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