19, 1 Perkins: The Octet Theory of Valence 19 
In comparing the halides of this group with those of Cr, Mo, 
W, and U, we find even stronger indications of definite shell- 
completing action than were noted in the preceding group. 
There seems to be no other explanation for the avoidance by 
S, Se, and Te of the apparent valences 3 and 5 except that they 
retain always their negative valence of 2, attracting halogen 
atoms beyond this amount only in pairs, and in the same way 
that NH, combines with HCl. 
EXAMPLES 
0x8=0 ye 
05 ee 
Di 3 O»Pad 
Hs O 3 
re) 
CH, F F os 
y VY é 
Hos ae | ee ee ee 
Pash, | 
CH; F F C] 
THE HALOGENS 
F—, Cl—-, Br—-, I~. 
Vacancies in shell =1. 
As these are typical negative atoms, there is no difficulty in 
representing their compounds. 
F 
+- 
F— Ff F— Br —F ae 
eel oe 
ie 
F F 
Cl 0 O O 
+ 8 8 | 
tO) H—O—I<O Ovl___.. It 
; g 
cl 6 a % 
O se 
CHI Le ee I 
