Lesson 3: Atomic Spectra, Bohr Model & Rydberg Formula
Demonstrating understanding of quantum phenomena, atomic structures, nuclear reactions, and special relativity.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Bohr's quantized electron orbits (angular momentum L = n h / 2π), photon emission/absorption during energy level transitions (ΔE = E_f - E_i = hf), Lyman/Balmer/Paschen series, and Rydberg equation 1/λ = R_H (1/n_f^2 - 1/n_i^2).
Calculate transition photon wavelengths using the Rydberg formula, construct energy level diagrams for hydrogen, and explain spectral line emission.
🎥 Media Anchor & Pedagogical Scaffold
The Bohr Model & Atomic Line Spectra
Video Clip: Atomic spectra — emission and absorption spectra, Bohr model energy levels | Khan Academy Physics (Runtime: 14m 43s).
🧠 1. Before Viewing (Activate & Predict)
Why do hot gases emit discrete sharp coloured lines instead of a continuous rainbow spectrum?
👁️ 2. During Viewing (Watch With a Job)
- Emission vs absorption: explain the difference between emission spectra and absorption spectra. Why does each element have a unique spectral 'fingerprint'?
- Bohr model: according to the Bohr model, in what orbits are electrons allowed to exist? What happens to an electron when it drops from a higher to a lower energy level?
- Rydberg: the video discusses energy level transitions. A hydrogen electron drops from n=4 to n=2. Describe what you would observe and what type of spectrum it belongs to.
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Set up discharge gas tubes (Hydrogen, Helium, Neon) and hand-held diffraction gratings for direct spectral line observation.
Immediate Task: Complete Section 3 of your Physics Portfolio: Hydrogen Spectral Line Calculations & Bohr Transition Diagramming.
⚡ Whakaoho | Do Now: Modern Physics Recall (10 mins)
How do we know what a star is made of? Nobody has been to one. Yet we can list a star's elements with confidence.
Two minutes: a sodium streetlight is orange, and a neon sign is red, and neither is a coincidence. Say what each element is doing to produce one specific colour rather than a spread — and what that means you could detect from light that has travelled a thousand years.
📖 Activity 1: Physics Concept Exploration & Problem Solving (25 mins)
Transitions to wavelengths (15 min). Using the Rydberg equation, calculate wavelengths for three transitions in the Balmer series. Identify which fall in the visible range. Then answer why the Lyman series is invisible to the eye, from the energy gaps rather than from memory.
Read an unknown spectrum (10 min). Given an emission spectrum with four lines, match it against the reference spectra provided and identify the element. Say which single line was decisive, and why a spectrum works as a fingerprint at all.
📝 Activity 2: Level 3 Physics Portfolio Task & Merit/Excellence Scaffolding (20 mins)
Portfolio — Section 3. Submit: (1) three Rydberg calculations with working and series identified; (2) an energy-level diagram with your transitions drawn and labelled with emitted wavelengths; (3) your unknown-element identification naming the decisive line, plus a paragraph on how stellar composition is determined.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 3 Alignment: Direct preparation for Level 3 Physics (Demonstrate understanding of application of modern physics). Emphasise clear physical explanations and multi-step mathematical working for Merit/Excellence grades.