526 Sir J. J. Thomson on the Structure of 



work for these processes respectively, it is easy to show that 

 if: the attraction is represented as on page 523 by 



n e Na6 



»-^!"("-l)'-("-«(-¥T}- 



Wi is always greater than W 2 . Jn-om these expressions 

 we find the following values for W 1 for different types of 

 atom. 



Gas. 



^Y l . 



VY 2 . 



Hydrogen.. 



le 2 



2* 



le 2 

 2* 



Lithium ... 



1 ,2 



~ r X -333 



1 a. 



U' 2 



2 -X-333 



Beryllium .. 



] e 2 

 2 - a -X-54 



o X "53 



-i Ci 



Boron 



] e 2 



2-X-62 



7> ~X # 5 

 z a. 



Carbon ,.. 



1<? 2 



;> ~ X "55 



le 2 



2 a - X -48 



Gas. 

 Nitrogen 



Oxygen 



Fluorine , 



Sodium 



W 



If.' 

 2* 



le l 



2a 



W 2 . 



le 2 



X-17 



lr 2 



2 a 



1,2 



X-4 



X-5o 



1 £2 



7, - X -09 

 la. 



X-4 



Thus the ionizing potential is least for lithium ; it then 

 rises sharply for beryllium, and remains nearly constant for 

 the rest of the period ; there is a great drop in passing to 

 sodium, and again a rapid rise, the ease with which the 

 atoms of the alkali metals are ionized in comparison with 

 those of other elements of the same period is very marked, 

 and accounts for the sensitiveness of the heavier alkali 

 metals to light of! long wave-length. 



The ionizing potentials in the preceding table relate to 

 atoms and not to molecules. 



Formation of Molecules. 



The molecules we consider are in the gaseous state, where 

 each molecule is separated so far from its neighbours that it 

 can be regarded as having an individual existence and not 

 merely as forming a brick in a much larger structure. The 

 term molecule when applied to the solid state is quite 

 ambiguous without further definition : for example, from 

 many points of view we can quite legitimately consider the 



