Chemistry / Unit 3: Electrons and the Periodic Table
3.2 Energy Levels and Atomic Spectra
Notes
In the Bohr model, electrons can have only certain energies, called energy levels ($n = 1, 2, 3, \ldots$).
- The lowest energy arrangement is the ground state. When an atom absorbs energy, an electron jumps to a higher level (excited state).
- When the electron falls back down, it emits a photon whose energy equals the gap between levels.
- Because only certain gaps exist, each element gives off only certain colors: its emission (line) spectrum, like a fingerprint.
- Bigger energy drops give higher-energy (shorter wavelength) light.
- Flame tests use this: sodium glows yellow-orange, copper green-blue, strontium red.
Practice
An atom emits light when an electron:
The energy lost by the electron as it falls is given off as a photon.
Why does each element have its own line spectrum?
Different energy gaps mean different photon energies, so different colors.
For hydrogen, which electron transition gives off the most energy?
The drop from $n = 4$ to $n = 1$ is the largest. Going from 1 to 4 absorbs energy instead of emitting it.
Ready for more? Take the Unit 3 test.