Explain the origin of the spectral series of hydrogen using Bohr's model. Name the series and their regions.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · State the rule. A fall from level n to level m gives one photon: hν = Eₙ − Eₘ = 13.6(1/m² − 1/n²) eV.
2 · Explain why lines are sharp. The levels are fixed, so only fixed energy gaps and fixed frequencies occur.
3 · Name the series.
Lyman: falls to n = 1, ultraviolet
Balmer: falls to n = 2, visible
Paschen, Brackett, Pfund: falls to n = 3, 4, 5, infrared
4 · Draw the level diagram with arrows. [Diagram: levels n = 1 to 5 and ∞; groups of arrows ending on 1, 2, 3, 4 and 5, labelled with the series names]
5 · Real life. Fraunhofer's dark lines in sunlight show hydrogen and other elements in the Sun.
6 · Close in one line. So, each series is a family of falls ending on the same level.
Scoring tip: A neat level diagram with labelled groups of arrows earns most of the marks. Write the region next to each series name.
