

the Molecule and Chemical Combination. 521 



has a unit negative charge. Since there is a positive 

 charge of 5 on the nitrogen nucleus and one of 4 on the 

 4 hydrogen atoms, there are 9 positive charges on the 

 -system NH 4 while it is surrounded by only 8 electrons : thus 

 on the balance there is a single positive charge on the 



•system (.xhA Thus the compound might be represented by 



(NH 4 ) + 01_, and would when electrolysed give NH 4 and 01 as 

 ions. In this case the molecule contains 2 cells of 8, one 

 surrounding the nitrogen core and the other that of the 

 chlorine. 



We have seen that the nitrogen atom could not take up 

 more than three hydrogen ones, so that we could not have the 

 compound NH 5 ; we could, however, have that represented 

 by NC1 5 . In this case each of the 5 electrons of the nitrogen 

 nucleus would have gone off to complete the tale of 8 elec- 

 trons round each of the 5 chlorine ions, and these cells would 

 surround the nitrogen atom. 



Those electrons on the shells round the 5 chlorine atom> 

 which are nearest to the nitrogen nucleus will form a layer 

 round the nitrogen atom, and we should not expect stable 

 equilibrium if the number of electrons exceeded 8. We should 

 get this arrangement if three of the layers round the chlorine 

 atoms presented an edge — each then would supply two elec- 

 trons to the nitrogen layer, the other two layers would each 

 present a corner and furnish one to the layer round the 

 nitrogen ; thus two of the chlorine atoms would be more 

 loosely attached to the nitrogen than the other three. 



The compound NC1 3 would also be possible on this scheme, 

 for an electron round the nitrogen nucleus might link up 

 with one from the chlorine and both form part of the layer 

 round the chlorine as well as that round the nitrogen, as the 

 number of electrons in the layer round the nitrogen nucleus 

 cannot be greater than eight ; since there are 5 already round 

 the nitrogen we can only get three chlorine atoms linked up 

 in this way. Thus it is possible to have the two chlorides 

 NCI3, NC1 5 ; though NC1 5 does not seem to have been pre- 

 pared, phosphorus which, like nitrogen, is a pentavalent 

 element, is known to have two chlorides, PC1 3 and PC1 5 . 

 If, instead of an atom with five electrons in the outer layer, 

 we had taken one like the atom of oxygen with six, it might 

 attach to itself in the way just described six atoms of 

 chlorine, and so be apparentlv hexavalent, as sulphur is in 

 the remarkable compound SF 6 discovered by Moissan. In 

 this way we are, as I pointed out in the paper on Chemical 

 'Combination already referred to, led to conclusions with 



