A continuous spectrum contains an uninterrupted range of wavelengths or frequencies, whereas a line spectrum contains only specific, discrete wavelengths. In IB Chemistry, line spectra provide evidence that electrons occupy quantized energy levels.
The Difference
| Feature | Continuous spectrum | Line spectrum |
|---|---|---|
| Appearance | An unbroken band of colours with no gaps | Separate bright or dark lines with gaps between them |
| Wavelengths present | All wavelengths within a range | Only particular wavelengths |
| Typical source | Hot, dense matter such as a solid, liquid or high-pressure gas | Excited atoms in a low-pressure gas |
| Atomic information | Does not show a unique atomic pattern | Produces a characteristic pattern for each element |
Why Does a Line Spectrum Form?
Electrons in atoms can occupy only particular energy levels. When an atom absorbs energy, an electron can move from a lower level to a higher level, producing an excited state.
When the electron returns to a lower energy level, the atom emits a photon. Its energy equals the difference between the two electron energy levels: