19 , 1 
Perkins: The Octet Theory of Valence 
11 
when ruptured, practically always gives the products — A — 
and B. The union A<-B may give A — and — B, but usually 
A and ^ B . 
Sometimes it is convenient for comparative purposes to 
express a loose, normal union by a long connecting line, and 
a close, strong union by a short line, as was done with salt- 
forming unions. A loose union is not necessarily polar: 
F — F I I. 
All of these distinctions of gradation are entirely unnecessary 
in an ordinary structural formula representing merely the out- 
standing valence relations, but are very valuable when attention 
is to be called to certain comparative characteristics. 
APPLICATIONS 
The mode of application of the proposed system to all of the 
atoms will be briefly indicated. It is believed that the rela- 
tions of the chemical properties of the atoms to the present 
theory of atomic structure will best be seen by grouping them 
(except H — and the group Sa — Lu) according to the horizontal 
lines in Table 1. 
HYDROGEN 
H— . 
Electrons in shell = 1. 
Vacancies in shell = 1. 
The hydrogen atom is unique in that its bare kernel (in this 
case the nucleus) can acquire a complete shell simply by 
attaching itself to any convenient pair of electrons not already 
shared by two kernels. This property accounts for the peculiar 
-f" 
mobility of the kernel, — H — , in molecules, which led to per- 
plexing controversies between organic chemists until it was 
finally recognized and called “tautomerism.” This property 
also distinguishes H — radically from all the other atoms 
having a negative valence of 1, giving it a pseudo-electropositive 
character. As Latimer and Rodebush 14 point out, the ionization 
of acids is not direct, like that of salts, but depends on a 
+ 
mobile (tautomeric) union of the — II— with molecules of the 
solvent. Thus H — Cl may be considered to give — H 1- Cl , 
w Latimer, W. M., and Rodebush, W. H., Journ. Am. Chem. Soe. 42 
(1920) 1425. 
