Part of JPH-02 — Atoms: Bohr Model & Hydrogen Spectrum

Excitation and Ionization

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  • Tags: excitation, ionization, energy
  • Difficulty: Moderate

Ionization energy from ground state: 13.6 eV (for hydrogen). From nth level: 13.6/n2n^{2} eV. First excitation energy (n=1 to n=2): 13.6 - 3.4 = 10.2 eV. Second excitation energy (n=1 to n=3): 13.6 - 1.51 = 12.09 eV. First excitation potential: 10.2 V. Ionization potential: 13.6 V.

When a photon of energy exactly matching a transition is incident, it is absorbed. If the photon energy exceeds the ionization energy, the electron is freed with KE = E_photon - 13.6/n2n^{2} eV. Photon energies not matching any transition are not absorbed — the atom is transparent to them.

When an electron (not photon) collides with a hydrogen atom, the electron can transfer any amount of energy (it's not quantized). But at least 10.2 eV must be transferred for excitation. If the colliding electron has KE < 10.2 eV, only elastic collision occurs.

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