Bohr’s postulates
Bohr postulated that only certain orbits were stable and that an atom only radiated energy when it made a transition from one level to another
the energy of a photon emitted was hf = Ei - Ef
since the energies of the orbits are related to their radii, f= (1/2)(kZe2/h)(1/r2 - 1/r1)
experimentally observed photon frequencies satisfied f=c/? = cR(1/n22 - 1/n12) where n1 and n2 are integers Rydberg-Ritz formula
do the allowed values of r ? n2 ?
If we think of the allowed orbits as standing waves then we need 2?r= n? for constructive interference