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.
🔑 Why This Matters
A line spectrum provides irrefutable proof that energy levels within atoms are strictly quantised. An electron can only exist in specific energy states, and never in the space between them. Each line corresponds to one exact energy transition.
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
As lines move toward higher frequencies within each series, the spacing between them steadily decreases. The lines converge. This reflects the fact that energy levels grow progressively closer together at higher values of n.
Energy Level Transitions
Arrows show electron transitions. The emitted photon's energy equals the gap between levels.