Lesson Plan

• Describe the concept of quantised atomic energy levels and photon emission/absorption.
• Apply the relationship hf = E_initial – E_final to calculate photon frequency and wavelength for hydrogen transitions.
• Convert energy differences from electron‑volts to joules and use c = λf to determine spectral‑line wavelengths.
• Analyse line‑spectra data to identify Balmer, Lyman, and Paschen series.
• Identify common errors such as swapping energy levels or neglecting unit conversion.

• Projector or interactive whiteboard
• Printed worksheet with hydrogen energy‑level table and practice questions
• Calculator or spreadsheet for unit conversions
• Scientific reference sheet with constants (h, c)
• Energy‑level diagram handout
• Laptop with a simulation (e.g., PhET “Models of the Hydrogen Atom”)

Begin with a striking image of the red H‑α nebular line to spark curiosity. Review the idea that electrons occupy discrete energy levels and that transitions produce photons. State that today students will master the formula hf = E₁ – E₂ and will be able to predict wavelengths of atomic spectra.

1. Do‑now (5'): Students calculate the wavelength for the n=3→2 transition using the provided energy table (quick check of prior knowledge).
2. Mini‑lecture (10'): Derive hf = E₁ – E₂, introduce constants h and c, and display an energy‑level diagram of hydrogen.
3. Guided practice (15'): Walk through the worked example on the board, students complete each step on their worksheet.
4. Collaborative activity (15'): In pairs, compute wavelengths for two assigned transitions (e.g., n=5→2 and n=4→3) and share results with the class.
5. Common pitfalls discussion (5'): Highlight typical mistakes (mixing up E₁/E₂, forgetting unit conversion) and have students correct a faulty calculation.
6. Exit ticket (5'): Write the wavelength of the Balmer H‑α line and one reason why the Balmer series appears in the visible region.

Summarise how the hf = E₁ – E₂ relationship links energy differences to observable spectral lines. Collect exit tickets to gauge understanding, and assign homework: three additional transition problems (including one from the Lyman series) to reinforce conversion skills.