Bohr Postulates and Scope
The Bohr model postulates stationary states with quantized angular momentum and photon exchange only during transitions. Its standard Coulomb formulas apply to hydrogen and hydrogen-like one-electron ions, not to general many-electron atoms.
Why this shows up in the exam
Recognizing hydrogen-like ions · Explaining discrete atomic spectra · Identifying limitations of classical atomic models
Learn the idea
Bohr's model stabilizes one-electron atoms by allowing only stationary quantized orbits. Classical orbiting charge would radiate and spiral inward. Bohr instead permits special orbits that do not radiate; light appears only when the electron jumps between them.
🧠 Memory hook: Stay in a stationary state; shine only while changing state.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- L = n h/(2 pi) = n hbar — angular-momentum postulate for positive integer n
- h nu = |E_i - E_f| — photon energy in a transition between stationary states
How to approach it
- 1Count bound electrons in the species
- 2State the relevant Bohr postulate
- 3Use a specialized formula only after confirming a one-electron Coulomb system
Common slip-ups that cost marks
- •Using Bohr formulas for neutral multi-electron atoms
- •Saying an electron radiates continuously in a stationary orbit
- •Treating the orbit as a modern literal electron trajectory
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
In hydrogen, an electron transitions from n = 2 to n = 1. Using E_n = -13.6/n^2 eV, find the emitted photon energy.
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