the Molecule and Chemical Combination. 533 



that each cell must have a heavily charged nucleus inside it 

 is to ensure stabilitj r . If the cell stood alone it would require 

 a positive charge of about seven units to ensure stability ; 

 when it forms one of a group and there are positive charges 

 outside it, it will not require so many inside to make it stable: 

 the assumption that four will be sufficient is an arbitrary one, 

 which fits in with chemical facts. It is clear that there must 

 be a lower limit, though its calculation would be long and 

 tedious. A simple way of determining the number of disposal 

 electrons is by the rule that it is equal to the sum of the 

 valencies of the atoms in the molecule : we must be careful, 

 however, when we apply this rule, to count the valency of 

 the halogens as seven and not one, that of oxygen and sulphur 

 as six and not two, and that of nitrogen and phosphorus as 

 five and not three. 



Perhaps the clearest way of seeing the differences between 

 the consequences of the view of combination we are discussing 

 and those of the ordinary theory of valency, is to consider 

 some special cases. 



Let us first take the case when there is only one cell : then, 

 to get the eight electrons required to complete this, a four- 

 electron atom must combine either with an atom with four 

 electrons, or preferably with a number of less highly charged 

 atoms, the sum of the charges on these atoms being equal to 

 four. A five-electron atom must combine either with a three- 

 electron atom, or singly or doubly charged atoms containing 

 altogether three electrons; the six-electron atom must combine 

 either with one two-electron atom or with two one-electron 

 atoms ; the seven-electron atom must combine with one 

 one-electron atom ; while the eight-electron atom could not 

 combine at all. These results are identical with those we 

 should arrive at from the ordinary theory of valency, 

 provided we ascribed to the 8, 7, 6, 5, 4 electron atoms 

 valencies 0, 1, 2, 3, 4 respectively. 



Let us now, however, consider the case when we have two 

 of these 8-electron cells connected together : these will 

 require 12 electrons if the two cells have four electrons in 

 common, 13 electrons if they have three in common, and 

 14 if they have two in common. We do not consider the 

 case when they have only one electron in common, as it 

 seems probable that this connexion would be too slight to 

 keep the two cells together. 



Thus if we have 12, 13, or 14 electrons at our disposal, and 

 only two highly charged atoms, we can make up a molecule 

 which will fulfil the conditions of saturation. Let us consider 

 the combinations possible for a four-electron atom. We shall, 



Phil. Mag. S. 6. Vol. 41. No. 243. March 1921. 2 N 



