The electron, its isolation and measurement and the determination of some of its properties

by Robert Andrews Millikan

Fig. 28—Hypothetical atomic structures

This gives, so Bohr believes, these penetrating electron-orbits in some cases a smaller mean potential energy, and therefore a higher stability, than some of the orbits corresponding to the smaller quantum numbers.

A glance at the group of elements beginning with argon, the last element in shell 3, in both [Table XV] and [Fig. 30], will make clear the meaning of this statement. The fourth column of [Table XV] shows that Bohr assigns to argon four very elliptical orbits of shape

and four of shape

. Glancing down the same column to copper, or lower, one sees that there are eighteen possible third-shell orbits, namely, six of shape

six of shape