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.
Last updated
Analogy
A piano has fixed notes, not every pitch in between. Electrons can only 'play' certain energy notes.
Example
Electron drops from n = 3 to n = 2.ΔE = 2.18×10⁻¹⁸ × (1/4 − 1/9) JΔE = 3.03×10⁻¹⁹ Jλ = 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.