The Bohr Atom (NOT Correct in detail!)
The allowed orbits are labeled by the integers: n = 1, 2, 3, 4.
The radii of these orbits can be determined from the quantization condition: radius = n2 a0 = n2 (h/2p)2/ me2
The energy can only have the values En= E1 /n2, E1 = - (1/2)(e2 / a0)/n2
The spectra are the result of transitions between these orbits, with a single photon (? = E/h) carrying off the difference in energy E between the two orbits.