Energy Levels and Line Spectra
An atom holds only certain electron energies, so a jump between two of them emits or absorbs a photon of one exact energy. That is why a hot gas gives bright lines and a cool gas in front of a lamp gives dark ones.
What a learner can do afterwards
- Calculates the wavelength emitted by a jump between two stated levels
- Reads an energy level diagram, including why the levels are given as negative numbers
- Explains an absorption spectrum as the same set of jumps taken the other way
1 · Read
An atom lets its electrons hold only certain fixed energies, like rungs on a ladder. When an electron drops from one rung to a lower one, the atom emits a photon carrying exactly the gap. A drop from -1.5 eV to -3.4 eV gives a 1.9 eV photon, and no other energy is possible for that jump.
The levels wear minus signs because the electron is trapped. Zero marks the escape point, where the electron just breaks free. Hydrogen sits deepest at -13.6 eV. Swallow a 10.2 eV photon and the electron climbs to -3.4 eV, since -13.6 plus 10.2 equals -3.4.
Absorption is the same jump taken the other way. Shine white light through cool hydrogen and photons with exactly the gap energy get swallowed to lift electrons upward. A photon of wavelength 656 nanometres lifts hydrogen from its second level to its third, leaving a dark line where that colour is missing.
Read a spectrum like a fingerprint. Hot gas gives bright lines on dark background, one per downward jump. Cool gas in front of a lamp cuts dark lines at the same positions. Each element owns a unique set of gaps, so its line pattern names it in stars and lamps.
Electrons jump between fixed levels, and each gap sends or swallows one photon of matching energy.
2 · Watch
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.