--- title: "Energy Levels and Line Spectra" description: "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 gi" canonical: https://lightmysky.com/learn/science/energy-levels-and-line-spectra-mt_RlMCSDxE5q source: https://lightmysky.com/learn/science/energy-levels-and-line-spectra-mt_RlMCSDxE5q.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # 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. Subject: Science · Area: Waves, Light & Sound · Ages 17 to 18 Page: https://lightmysky.com/learn/science/energy-levels-and-line-spectra-mt_RlMCSDxE5q ## Ready when they can - 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 ## Lesson: Why atoms glow in single colours 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. **Example.** 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. **Tip.** 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. **Recap.** Electrons jump between fixed levels, and each gap sends or swallows one photon of matching energy. ## Practice 13 questions on this page, each with its working shown. ## Needs first - [Electron Shells and the Shape of the Periodic Table](https://lightmysky.com/learn/science/electron-shells-and-the-shape-of-the-periodic-table-mt__Sdcw4RnZF) - [The Photoelectric Effect and the Work Function](https://lightmysky.com/learn/science/the-photoelectric-effect-and-the-work-function-mt_ADQK7WB2JN) ## Opens up - [Stellar Spectra, Spectral Classes and Surface Composition](https://lightmysky.com/learn/science/stellar-spectra-spectral-classes-and-surface-composition-mt_4FBh5G7Gdc) - [Blackbody Radiation and the Quantum of Energy](https://lightmysky.com/learn/science/blackbody-radiation-and-the-quantum-of-energy-mt_B2Bk2IAOa9) - [Atomic Absorption and Emission for Trace Metals](https://lightmysky.com/learn/science/atomic-absorption-and-emission-for-trace-metals-mt_NfQWURds_H) - [The Schrodinger Equation and What a Wavefunction Says](https://lightmysky.com/learn/science/the-schrodinger-equation-and-what-a-wavefunction-says-mt_WCwbaO9rpR) - [de Broglie Waves and Electron Diffraction](https://lightmysky.com/learn/science/de-broglie-waves-and-electron-diffraction-mt_Y8NthsmPcv) - [Separating the Schrödinger Equation for Hydrogen](https://lightmysky.com/learn/science/separating-the-schrodinger-equation-for-hydrogen-mt_Yk2qHB0_v2) - [The Hertzsprung-Russell Diagram and Stellar Evolution](https://lightmysky.com/learn/science/the-hertzsprung-russell-diagram-and-stellar-evolution-mt_zMZDIB5TGc)