Bohr said that the only way an electron can lose energy is by dropping from one energy level to a lower one. When
this happens, the atom emits visible light, in response to the difference in energy levels. As long as electrons stay
in their orbits, electrons don't have to lose any energy. And, if an electron is in the lowest energy level already, it
can't lose any energy.
If an electron is in a higher level, and wants to drop to a lower level, it can. But not if that lower level is
filled with another electron.
Bohr made rules stating how many electrons can be in any level at the same time...but we do not know of these
rules yet!
The major shortcoming of the Bohr Model of the atom, however, was that it could not predict energy levels for more than
one electron.
