19,1 Perkins: The Octet Theory of Valence 13 
THE LITHIUM GROUP 
I I I i 
I 
ik NA RR, oe, 
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: 
THE BERYLLIUM GROUP 
il ll il it Il il 
Ge. Me. CA, Sty Be. Re 
Electrons in shell — 2. 
These atoms are similar to the lithium group except that 
each loses 2 electrons: 
Ill Ill 
oe 
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! is due to the fact that 
Sc M1 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.* 
* ef. Langmuir, ibid. p. 929. 
