Point 4 of 27 — Lesson 1: Hydrogen Atomic Emission Spectrum and Production of X-RaysQuestion bank: 1 questions (1 with pictures)
04Excitation and emission in hydrogen
When hydrogen gas is excited (for example by an electric discharge), not all atoms are excited in the same way. In different atoms the electron is raised from the first level K (n = 1) to different higher levels (n = 2, 3, 4, ...). A single atom's electron makes one jump at a time; the many atoms together give all possible jumps.
The electron remains in an excited level only for a very short time, the lifetime (about 10⁻⁸ s), and then returns, directly or by steps, to the lowest level (the ground state).
During the fall from level nito level nf the atom emits a photon with
h ν = Ei− Ef = 13.6 (1/nf² − 1/ni²) eV, with wavelength λ = hc/(Ei− Ef).
In terms of wavelength this is theRydberg formula: 1/λ = RH (1/nf² − 1/ni²), RH = 1.096 × 10⁷ m⁻¹.
Each possible jump has one definite energy difference and therefore one definite frequency and wavelength. That is why the spectrum of hydrogen consists of lines, not a continuous band.
An atom with N levels excited can show N(N−1)/2 different lines (for four levels, six lines).
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