On the constitution of atoms and molecules

by Niels Bohr

For the atoms of the elements considered in the former section we have assumed that the two electrons first bound are arranged in a single ring, and, further, that the two next electrons are arranged in another ring. If

the configuration

will correspond to a smaller value for the total energy than the configuration

. The greater the value of

the closer will the ratio between the radii of the rings in the configuration