Interactive spectroscopy visualisation showing how atomic emission spectra reveal quantised energy levels
Every atom confesses its identity through the gaps
A hot gas of one element doesn't glow in a full rainbow like a hot solid does; it emits only certain sharp wavelengths, like a barcode stamped in light. Those missing colours are the proof that electrons can't sit anywhere: energy is quantised. Move the electron between energy levels and watch the photon that escapes.
Hydrogen emission
n=3 → n=2
Electron drops down a level; a photon escapes with E = hf
656 nm · Visible red (Hα)
Upper energy level (n)
n=2n=3n=4n=5n=6
Energy jump (eV)
1.89
Wavelength (nm)
656
Heat hydrogen gas and it glows at sharp wavelengths — 656 nm red, 486 nm cyan, 434 nm violet. Each line is one electron dropping from a higher level to n=2 (the Balmer series); the n=2 setting is the odd one out, an ultraviolet drop to n=1 (Lyman α). The photon’s energy equals the gap: E = hf, so bigger jumps make bluer light. Every element has a unique set of allowed levels, so every element has a unique spectrum — astronomy’s greatest forensic tool.
Know This
Atomic spectra are discrete lines because electrons occupy quantised energy levels, and each photon released carries exactly the energy difference between two levels.