| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Chemistry |
| Lesson Topic: Define mass number / nucleon number as the total number of protons and neutrons in the nucleus of an atom |
Learning Objective/s:
- Define mass number and distinguish it from atomic number.
- Explain how mass number identifies isotopes of an element.
- Calculate mass number using the numbers of protons and neutrons.
- Interpret isotope notation to determine proton, neutron, and mass numbers.
- Apply the concept of mass number to solve basic practice problems.
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Materials Needed:
- Projector or interactive whiteboard
- PowerPoint slides with isotope tables
- Handout containing practice questions
- Model of an atom (ball‑and‑stick or labelled diagram)
- Worksheet for calculations
- Whiteboard and markers
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Introduction:
Begin with a quick mental‑math hook: “If an atom has 8 protons and 9 neutrons, what is its mass number?” Connect this to prior knowledge of atomic number and isotopes, and state that today students will be able to define and use mass number accurately.
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Lesson Structure:
- Do‑Now (5') – Students answer the hook question on a sticky note; teacher reviews responses.
- Mini‑lecture (10') – Define mass number, present A = Z + N, and discuss its role in distinguishing isotopes using slides.
- Guided practice (12') – Work through the carbon isotope table together; students fill a similar table for chlorine isotopes.
- Independent practice (10') – Complete worksheet with three practice questions; teacher circulates for support.
- Check for understanding (8') – Quick quiz via clicker/online poll; discuss correct answers.
- Summary & Exit ticket (5') – Students write one sentence summarising why mass number matters and answer a short exit question.
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Conclusion:
Recap the definition of mass number and its importance for identifying isotopes. Collect exit tickets to gauge understanding, and assign a short homework task: calculate the mass numbers for five given isotopes and explain the difference between each pair.
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