1.3.1—Emission spectra
- Syllabus
- First assessment 2025
- Objective
- 1.3.1
- Level
- HL
Emission Spectra
An emission photon is released when an electron falls from a higher energy state to a lower energy state. Absorption moves an electron upward and requires photon energy.
| Spectrum | What it contains | Why |
|---|---|---|
| Line spectrum | Specific wavelengths, frequencies, energies, or colours | Electrons occupy discrete energy levels, so only particular transitions occur |
| Continuous spectrum | A continuous range across the relevant values | The radiation spans the range rather than appearing as separated lines |
Across electromagnetic radiation, shorter wavelength means higher frequency, and higher frequency means higher photon energy. Explain the electron direction and photon exchange when distinguishing absorption from emission.
Read every spectral transition in two directions: absorption raises an electron by ΔE, while a downward transition emits a photon with ΔE = hf = hc/λ. A shorter-wavelength line therefore represents a larger energy gap, not a higher line intensity.
Orient the spectrum before comparing lines: radio → microwave → infrared → visible → ultraviolet → X-ray → gamma is increasing frequency and photon energy, and decreasing wavelength. Within visible light, red has longer wavelength and lower photon energy than violet.