Using Bohr's model, explain how hydrogen gives an emission line spectrum and an absorption line spectrum. Draw an energy level diagram showing a few transitions.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · State the frequency condition. When the electron falls from a higher level to a lower one, it emits a photon: hν = E(initial) − E(final).
2 · Explain the bright lines. The levels Eₙ = −13.6/n² eV are fixed, so only certain energy gaps and wavelengths are possible: bright lines on a dark background.
3 · Explain the dark lines. In cool hydrogen, an electron takes in only a photon whose energy exactly matches a gap, so dark lines appear at the same wavelengths.
4 · Draw the diagram. [Diagram: levels n = 1 to 5 and ∞ with energies in eV, closer together going up; downward arrows for falls such as 2 → 1, 3 → 2 and 4 → 2]
5 · Close in one line. So, each spectral line is the fingerprint of one jump between two fixed levels.
Scoring tip: Draw the levels closer together as n increases and write the energy in eV beside each level. That earns the diagram mark.
