Chapter 9 · Electrons in Atoms and the Periodic Table
9.4The Bohr Model: Atoms with Orbits
9 min · two checks
Predict
What happens to an electron that falls from a higher Bohr orbit to a lower one?
The idea
- Describe emission and absorption in the Bohr model.
- State the model’s limit.
Bohr pictured the electron of hydrogen on orbits with fixed energies, labeled by n = 1, 2, 3, and up. The electron does not radiate while it stays on an orbit. It emits one photon when it drops to a lower orbit, and it absorbs one photon to climb. The photon energy equals the gap. That single idea explains hydrogen’s line spectrum, including series of lines that had looked like number games.
The orbits are a sketch, not a path you could film. The model does not correctly describe atoms with more than one electron, because electrons repel each other and the levels split. What survives into the next model is quantization: electrons occupy states with definite energies, and light reports the differences.
Keep these
- Photon energy equals the difference between levels.
- Emission is a downward jump. Absorption is an upward jump.
- Bohr works for hydrogen’s spectrum and fails as a literal map for bigger atoms.