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Bohr's model: fixed orbits and energy levels sheet
3-mark answer frame

State Bohr's postulates. How does his model explain the stability of an atom?

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Postulate 1. Electrons move in fixed circular orbits (energy levels K, L, M, N) around the nucleus.
  2. 2 · No energy loss. In these stationary states an electron gives out no energy.
  3. 3 · Postulate 2. An electron jumps to a higher level by absorbing energy and falls back by giving it out: E = hν = E₂ − E₁.
  4. 4 · Diagram. Nucleus with labelled K, L, M, N circles and an arrow for a jump.
  5. 5 · Stability. Since no energy is lost in an orbit, the electron never spirals into the nucleus, so the atom is stable.
  6. 6 · Close. So Bohr's model removed Rutherford's stability problem.

Scoring tip: Write 'does not lose energy' in so many words; it is the key phrase for the stability mark.