Investigate how discrete atomic energies produce photons and line spectra. The A-level lab links a three-dimensional atomic representation with a selectable energy diagram and a spectrometer.
What you can investigate
- Photon energy, frequency and vacuum wavelength
- Classical, Bohr and hydrogen probability-cloud representations
- Selectable energy levels and supported photon transitions
- Emission and state-dependent absorption spectra for five elements
- Ionisation and electron kinetic energy
- Custom energy diagrams and captured calculations
Where does hydrogen’s red spectral line come from?
- Select hydrogen and the 3s → 2p transition. Hide the calculated answers and use the level energies to predict the photon wavelength.
- Emit one photon and follow its arrival at the detector. Reveal the calculation and capture it in the notebook.
- Reverse the transition and send a matching photon. Compare with a photon of a different energy, then try a ground-state atom.
- Open Spectra and compare ground-state absorption with a prepared n = 2 state. Explain why their visible spectra differ.
Photon energy equals the magnitude of the atomic energy change. A supported absorption transition also requires the appropriate occupied lower state. Balmer absorption begins in n = 2, while the ground state absorbs Lyman wavelengths in the ultraviolet.
Interpreting the model
Hydrogen uses nonrelativistic eigenstates and Eₙ = −13.6/n² eV. Other atoms use selected neutral-atom levels and transitions from NIST. All wavelengths are in vacuum. Curated line sets, assumed populations and instrument broadening define the model spectra; these are not calibrated discharge-lamp predictions. Spatial scales, lifetimes and photon flight times are enlarged for teaching.
Revision and practice