How do we know that electrons in atoms occupy quantised energy levels when we cannot see the electrons themselves? This concise FranklyChemistry video uses the hydrogen emission spectrum as the experimental evidence. Students are guided through: continuous spectra compared with line emission spectra electron transitions and the emission of photons the relationship between energy, frequency and wavelength the Balmer series and electron transitions to (n = 2) why successive Balmer lines become progressively closer together how this convergence reveals that the higher electron energy levels become closer together the Balmer series limit and its connection with ionisation The emphasis throughout is on understanding the experimental evidence rather than simply memorising an energy-level diagram. Suitable for A-level Chemistry, International A-level Chemistry, IB Chemistry and other advanced secondary chemistry courses. FranklyChemistry — Where Chemistry Questions Get Proper Answers. Scan the QR code to explore the FranklyChemistry Chemistry Roadmap and related resources.