Lesson Plan

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Lesson Plan
Grade: Year 12 Date: 17/01/2026
Subject: Chemistry
Lesson Topic: Mass spectrometry: principles, interpretation
Learning Objective/s:
  • Describe the three main steps of mass spectrometry (ionisation, mass analysis, detection).
  • Explain how to locate the molecular ion and use the nitrogen rule and isotopic patterns to determine molecular formula.
  • Apply common fragmentation rules (α‑cleavage, McLafferty rearrangement, neutral losses) to interpret a spectrum.
  • Compare electron‑impact and chemical ionisation techniques and their effect on fragmentation patterns.
Materials Needed:
  • Projector and PowerPoint slides on MS principles
  • Printed handouts with example mass spectra
  • Worksheet for guided practice
  • Calculator for m/z calculations
  • Whiteboard and markers
  • Exit‑ticket slips
 Introduction:
Begin with a short video of a mass spectrometer in operation to capture interest. Ask students to recall how they previously determined molecular formulas using combustion analysis and how fragmentation can reveal functional groups. Explain that today they will learn how mass spectrometry provides rapid molecular mass and structural clues, and they will be able to identify the molecular ion, apply the nitrogen rule, and interpret key fragments by the end of the lesson.
Lesson Structure:
  1. Do‑now (5’) – Quick quiz on isotope patterns and the nitrogen rule from the previous lesson.
  2. Mini‑lecture (10’) – Overview of mass‑spectrometry principle and main components using slides.
  3. Demonstration (8’) – Walk through a sample spectrum, point out M⁺, isotopic peaks, and contrast EI vs CI ionisation.
  4. Guided practice (12’) – Pairs analyse a printed spectrum, identify the molecular ion, apply the nitrogen rule, and list likely fragments on a worksheet.
  5. Whole‑class discussion (8’) – Groups share interpretations; teacher clarifies fragmentation rules (α‑cleavage, McLafferty, neutral losses).
  6. Exit ticket (5’) – Each student records the molecular‑ion m/z and one justified fragment; tickets collected for assessment.
Conclusion:
Summarise how the molecular ion, isotopic patterns and fragmentation rules combine to reveal molecular formula and sub‑structures. Review the success criteria and confirm that students met them through the exit tickets. For homework, assign three unknown spectra for students to analyse using the steps learned.