| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Chemistry |
| Lesson Topic: Define isotopes as different atoms of the same element that have the same number of protons but different numbers of neutrons |
Learning Objective/s:
- Describe the definition of isotopes and differentiate between atomic number and mass number.
- Explain how isotopes affect atomic‑mass calculations and why elements have weighted‑average atomic masses.
- Identify isotopes of common elements and write correct isotope notation.
- Analyse practical applications of isotopes such as radiometric dating and tracer studies.
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Materials Needed:
- Projector and screen
- Whiteboard and coloured markers
- Isotope notation worksheet
- Periodic‑table handout
- Isotope “card” set (e.g., H, C, Cl examples)
- Calculators
- Exit‑ticket slips
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Introduction:
Begin with the question “What if two atoms of the same element could weigh different amounts but still behave chemically the same?” Students recall that protons determine element identity and that they already know about neutrons and atomic mass. State the success criteria: by the end of the lesson students will be able to define isotopes, write isotope notation, and calculate an element’s average atomic mass.
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Lesson Structure:
- Do‑now (5'): Students answer two quick revision questions from the source (definition of isotope; identify protons, neutrons, mass number for a given isotope).
- Mini‑lecture (10'): Teacher presents the definition, notation \(^{A}_{Z}\text{X}\), and key concepts (constant Z, variable N, physical vs chemical properties).
- Guided practice (15'): Using the worksheet, learners calculate the average atomic mass of chlorine from given isotopic abundances.
- Interactive activity (10'): In pairs, students match isotope cards to their correct notation and discuss stability vs radioactivity.
- Check for understanding (5'): Whole‑class “exit ticket” – write the definition of an isotope in their own words.
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Conclusion:
Recap the definition of isotopes, the notation system, and how isotopic mixtures give rise to average atomic masses. Collect the exit tickets to gauge understanding, and assign a short homework task: calculate the average atomic mass of sulfur using provided isotopic data.
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