# Atomic emission spectrum

When atoms are heated, they give off light at only a few exact colours. Each element has its own set of colours. This shows that electron energies are fixed steps, not a smooth range.

Chemistry (university) · Part 01: Atomic structure and periodic trends · Card 1 of 10 · Last updated 2026-10-19

## Analogy

A piano has fixed notes, not every pitch in between. Electrons can only 'play' certain energy notes.

## Example

**Hydrogen red line**

Electron drops from n = 3 to n = 2.
ΔE = 2.18×10⁻¹⁸ × (1/4 − 1/9) J
ΔE = 3.03×10⁻¹⁹ J
λ = hc/ΔE = 656 nm (red)

## In practice

Chemists identify elements in stars and fireworks by the colours of light they give off.

## Practice

### Flashcards

- **Why do atoms give line spectra, not a rainbow?** Electron energies are quantised, so only certain jumps and colours are possible.

## Questions people ask

### Why do atoms emit only certain colours of light?

An electron can only sit at certain fixed energy levels. When it drops from a higher level to a lower one, it releases exactly the energy difference as one photon. Because the gaps are fixed, only certain light colours (wavelengths) appear. This is why each element has a unique line pattern.

### How does an emission spectrum differ from an absorption spectrum?

An emission spectrum shows bright lines on a dark background, made when excited atoms release light. An absorption spectrum shows dark lines on a bright rainbow, made when atoms take in light. The lines sit at the same wavelengths because both come from jumps between the same energy levels.

## Related concepts

- [Photon energy](https://studyvisually.com/learn/science/chemistry-university/chemistry-university-part-1/chemistry-university-part-1-concept-2)

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