19, 6 
Perkins: Chlorine Dioxide and Compounds 
739 
tain peculiarities such as the combination of sulphuric acid and 
water now generally considered as secondary valence reactions. 
The three-electron bond, on the other hand, is undoubtedly found 
in benzene and all the thousands of benzenoid derivatives. 
A consideration of organic compounds being deferred to a 
later paper, 12 two inorganic odd molecules will now be discussed 
briefly. 
NITROGEN DIOXIDE 
This compound (VI) is analogous to chlorine dioxide. 
0 
II 
(VI) 0 — N “ 0 (VII) N — 0 — N _ 0 
ft 
0 
It is to be expected that the quadricovalent nitrogen in the as- 
sociated form (VII) of this compound has a greater electron 
binding strength than tricovalent chlorine in the analogous com- 
pound C1 2 0 4 . This is due not only to the smaller size of the ni- 
trogen kernel, but also to the fact that a double bond with 
oxygen causes more displacement of electrons than two single 
bonds with unicovalent oxygen atoms. Therefore N0 2 asso- 
ciates to some extent in the gaseous condition, and entirely when 
in the liquid condition. 
NITRIC OXIDE 
When ten or more electrons gather around a single nucleus 
they always form a kernel pair surrounded closely by an octet. 
The kernel pair not surrounded by an octet is stable when at- 
tached to a nucleus of small charge, such as He, Li, Be, and Bo. 
Langmuir 13 has explained the properties of the nitrogen mole- 
cule and some similar compounds by assuming that the two 
nuclei retain their stable kernel pairs and share between them an 
extra pair, leaving eight electrons to form an octet around this 
double kernel. It is hardly more than a restatement of this 
explanation to say that when a kernel pair is attached to a nucleus 
carrying a positive charge of six or more, and is not stabilized 
by a closely surrounding octet, it is no longer the most stable 
group which can surround the nucleus, but is superseded by a 
group of four. In the nitrogen molecule, then, the nuclei are 
12 Cole, H. I., Philip. Journ. Sci. 19 (1921) 681, has already discussed 
in detail the triphenyl aryls, which form odd molecules under certain con- 
ditions. 
13 Cf. page 731, footnote 6. 
