Scientific model
For a one-electron species, level energy is −13.6 × Z² ÷ n² electron volts. A photon is absorbed only when its energy matches an upward gap. A downward jump emits a photon with the same energy difference.
Applications
Energy-level transitions explain emission lamps, stellar spectra, lasers, flame tests, and astronomical element identification. Electrons do not orbit as tiny classical planets; the rings are a useful energy-level visualization.