Bohr Model — Flashcards & Quiz

Key Points

• Bohr's postulates: electrons orbit the nucleus in discrete circular orbits; angular momentum is quantised (L = nħ).
• Hydrogen energy levels: E_n = –13.6/n² eV. Ground state is n = 1 (–13.6 eV); n → ∞ is 0 eV (ionisation).
• Transitions between levels absorb or emit photons: ΔE = E_f – E_i = hf = hc/λ.
• Spectral series: Lyman (to n = 1, UV), Balmer (to n = 2, visible), Paschen (to n = 3, infrared).
• Rydberg formula: 1/λ = R(1/n₁² – 1/n₂²), where R is the Rydberg constant and n₁ < n₂.
• The Bohr model explains the hydrogen spectrum but fails for multi-electron atoms — superseded by quantum mechanics.

Common Mistakes to Avoid

1. Forgetting the negative sign in E_n = –13.6/n² eV — bound electrons have negative total energy.
2. Using the wrong n values in the Rydberg formula — n₁ is the LOWER level, n₂ is the UPPER.
3. Confusing absorption (lower to higher energy) with emission (higher to lower).
4. Applying the Bohr formula to multi-electron atoms — it only works precisely for hydrogen.
5. Not converting between eV and J (1 eV = 1.6 × 10⁻¹⁹ J) when calculating wavelengths.

Exam Strategy

TASC Level 4 Bohr model questions ask you to calculate transition energies, identify spectral series, or explain the hydrogen spectrum. Method: (1) use E_n = –13.6/n² to find initial and final energies, (2) calculate ΔE, (3) apply ΔE = hc/λ for photon wavelength, (4) identify the series (Lyman/Balmer/Paschen) based on the lower n.

Revision Tip

Hydrogen spectrum calculations are procedural — drill a Revizi deck with 10+ transitions varying both initial and final n values.