i9, i Perkins: The Octet Theory of Valence • 9 
It is obvious that in any aggregate of an atomic kernel and 
20 , 30 , 40 and in such complexes as Cr 2 0 7 , an octet 
way be formed around the kernel, and in many cases probably is 
formed. Therefore the formulas of such aggregates in which the 
central atom has a valence of 4, 5, 6, or 7 could be written in ex- 
actly the same manner as those of the analogous ions containing 
— C — , — N — , — S — , and Cl — , which also contain 4, 5, 6, 
I I 
and 7 electrons in the shell, respectively. The distinction, as 
it appears to the writer, is that in one class of cases all the 
known facts are as well explained on the basis of ordinary 
electrostatic attraction alone (subsequent to ion formation) as 
they are by assuming an effective tendency of the electrons sur- 
rounding the kernel in question toward octet formation, but 
that in another class of cases we have definite evidence that 
there is an effective tendency toward octet (or other stable shell) 
formation. The writer prefers to use the salt-forming symbol 
for the former class and the direct symbol for the latter. 
GRADATIONS IN THE ELECTRONEGATIVE TENDENCY 
An atom is called electronegative (in the chemical sense) 
when it shows a tendency to become negatively charged. As 
has just been intimated, the distinguishing characteristic of 
a negative atom is that it shows a definite tendency toward 
building up some stable arrangement, usually an octet, of elec- 
trons. A discussion of the forces involved is beyond the scope 
of this paper. 13 It is necessary only to point out that there are 
observed differences in the electronegative tendencies of atoms. 
Fluorine is the most strongly negative, and starting from this 
u It is illogical to try to apply very closely to this case the laws of elec- 
trostatics as we know them. Latimer and Rodebush, Journ. Am. Chem. Soc. 
42 (1920) 1425, treat electronegativity practically as an ordinary elec- 
trostatic phenomenon, arriving at the conclusion that “In one sense then, 
hydrogen is the most electronegative of all the elements.” Langmuir, 
Journ. Am. Chem. Soc. 41 (1919) 908, approaches this problem more 
reasonably, concluding that “Hydrogen therefore can hardly be classed 
as an electronegative element.” He proceeds, however, to apply (page 
910) the inverse square law to the total force between the nucleus 
and the shell in the case of carbon and other atoms, although later 
(page 932) he suggests the fact that the whole existence of the shells 
depends on some such balance of forces as a discontinuous inverse squai-e 
attraction opposed by an inverse cube repulsion. 
It would seem necessary to use caution in applying any force laws to 
the shell electrons, especially regarding the attraction of the nucleus. 
