36 SECTIONAL ADDRESSES. 
The states 4,5, 6, . . . are to be considered as those which give rise 
to the o terms in the series arc spectrum of potassium. The states 
4, 5, 6, connote the z spectral terms, and the states 3,, 4, the 3 
spectral terms. The state 4, will give rise to one of the ¢ or funda- 
mental terms in the series spectrum. 
FIG. 2.—Binding Potassium Orbits. 
Grotrian’s method of exhibiting these relationships is instructive. 
Its application to the case of the stationary orbits of the potassium 
atom is shown in Fig. 3. 
A few outstanding features of the classification given in Table I. 
may be referred to. In the first place, the scheme provides for periodi- 
city in the properties of the elements. For example, in the case of 
r 
n 
| 72x 15 2:0 25 30 4 56 
rt Tar et: <a | T 7 a sa 
a 4@<—~-+---~--- 5e@7—- 
Ts K (19) Bis Sees el 
! cs ~ 
& Se Tee 
a) ' | 40-0 — 
fe jae ! Ue ENG Bl ee ee eee A SLi 
U 50000 40000 30000 20000 10000 0 
Fic. 3.—Grotrian Diagram. 
the heavier inert gases the outer group of electrons is made up of two 
sub-groups with four electronic orbits of the same type in each. For 
these sub-groups the subordinate quantum number has the values 1 and 
2. The principal quantum number increases by unity from element to 
element. Again, in the case of the alkali elements the outer group con- 
tains but one orbit. For it the subordinate quantum number k has 
the characteristic value 1, and the principal quantum number again 
