19 , 1 
Perkins: The Octet Theory of Valence 
13 
THE LITHIUM GROUP 
I I I I i 
Li , Na , K , Rb , Cs . 
Electrons in shell — 1. 
The atoms of this group have an electropositive valence of 1. 
Their outer shells are too incomplete for the formation of 
completed shells, and therefore they enter only into salt-forming 
unions : 
+ 
+ 
+ 
Li - 
- Cl 
, Li 
- 0 -- 
Li , 
+ 
+ 
+ 
Li - 
H , 
Na - 
- Cl , 
Cs — - 
-- Cl 
THE 
BERYLLIUM 
GROUP 
ii 
II 
II II 
II 
ii 
Be , 
Mg , 
Ca , Sr 
, Ba , 
Ra . 
Electrons in shell = 2. 
These atoms are similar to the lithium group except that 
each loses 2 electrons: 
++ + + 
Be :::::: 0 , Cl Ca CP, 
Br Ra Br . 
THE BORON GROUP 
III I III I III III 
B ( — B — ), A1 ( - A1 - ), Sc , Yt , 
/ \ / \ 
hi hi 
La , Ac . 
Electrons in shell = 3. 
This group is predominantly electropositive. Under favor- 
able circumstances, however, the first two members can complete 
their outer shells, thus exhibiting a negative valence of 5. That 
this property stops abruptly with Al m is due to the fact that 
Sc 111 would require 15 electrons, instead of 5, to complete its 
shell. 
The compounds in which B is electropositive are not at all 
typical saltlike compounds. The negative ions surround the 
small B+++ kernel so completely and so' closely that the exter- 
nal field is small and rupture of the union very difficult. 16 
16 cf. Langmuir, ibid. p. 929. 
