When the light emitted by excited hydrogen atoms is passed through a prism or diffraction grating, it does not produce a continuous rainbow. Instead, it produces a discontinuous line emission spectrum. Discrete, sharply defined lines of specific frequencies against a black background.
Proof of Quantised Energy Levels
A line spectrum provides irrefutable proof that energy levels are quantised. Electrons cannot possess intermediate energy values; they can only occupy specific, defined orbits.
The Three Series of Hydrogen
Because hydrogen has only one electron, its spectrum is free from inter-electron repulsion complexities. Transitions returning to different base levels create distinct spectral series:
| Series | Transitions To | Energy | Region |
|---|---|---|---|
| Lyman | n = 1 (ground state) | Highest energy drops | Ultraviolet (invisible) |
| Balmer | n = 2 | Moderate energy drops | Visible light |
| Paschen | n = 3 | Smallest energy drops | Infrared (invisible) |
Energy Level Convergence at Higher Frequencies
As lines move toward higher frequencies within any series, the distance between them shrinks until they form a continuum. This demonstrates that energy levels within the atom become increasingly closely spaced at higher values of \(n\).
Arrows show electron transitions. The emitted photon's energy equals the gap between levels.
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