| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: Know that isotopes of an element may be radioactive due to an excess of neutrons in the nucleus and/or the nucleus being too heavy |
Learning Objective/s:
- Describe what isotopes are and how the neutron‑to‑proton ratio influences nuclear stability.
- Explain why an excess of neutrons or a very heavy nucleus causes radioactive decay.
- Identify the main decay types (α, β⁻, β⁺, γ) and the conditions for each.
- Interpret a valley‑of‑stability diagram to predict decay pathways.
- Apply the half‑life formula t½ = ln 2 / λ in simple calculations.
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Materials Needed:
- Projector or interactive whiteboard
- Slide deck with isotope and decay diagrams
- Printed worksheet with isotope tables and decay equations
- Colored cards representing α, β⁻, β⁺, and γ particles
- Calculator for half‑life calculations
- Access to an online nuclear decay simulation (e.g., PhET)
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Introduction:
Begin with a quick poll: “Which elements do you think are radioactive and why?” Connect this to prior learning about atomic structure, then state that by the end of the lesson students will be able to explain how neutron excess or nuclear mass leads to radioactivity and identify the resulting decay type.
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Lesson Structure:
- Do‑now (5') – short quiz on isotopes and N/Z ratios.
- Mini‑lecture (10') – present key concepts and reasons for instability with slides.
- Interactive diagram activity (12') – groups place given isotopes on a valley‑of‑stability chart and predict decay modes.
- Simulation demonstration (8') – run an online decay simulation to observe α and β⁻ emissions.
- Worksheet practice (10') – solve problems on decay equations and half‑life calculations.
- Check for understanding (5') – exit ticket: write one reason an isotope may be radioactive and its likely decay type.
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Conclusion:
Recap that isotopic stability depends on the neutron‑to‑proton ratio and overall nuclear mass, with excess neutrons favouring β⁻ decay and very heavy nuclei favouring α decay. Collect the exit tickets and remind students to complete the homework: classify a set of isotope cards and calculate a half‑life using the formula provided.
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