

the Molecule -and Chemical Combination. 519 



in the outer ring', such as that of Fl or 01, can have the same 

 •valency as an atom containing only one electron. 



Fio-. 2. 



-B 



Suppose that A (fig. 2) is the centre of the 7 electron 

 atom, B that of a 1 electron atom. Let u be an electron on 

 the first atom, j3 one on the second, It these electrons place 

 themselves somewhat as in the figure,! the attractions they 

 exert on A and B may keep these together in spite of the 

 repulsion between the positive charges A and B, while the 

 attractions A and B exert on a and jS may keep these to- 

 gether in spite of the repulsion between them. The addition 

 of ft to the seven electrons already round A will raise the 

 number in the outer layer round A to eight. Now suppose 

 we attempted to attach another 1 electron atom B' to A. 

 This would introduce another electron in the layer round A, 

 raising the number in this layer to 9. But .we have seen 

 that 9 electrons in one layer cannot be kept in stable equi- 

 librium by a positive charge of nine units, but 9 units of 

 positive electricity is all we have at our disposal, and two of 

 these units are outside the layer : though they are outside 

 they will make the arrangement of the electrons more stable 

 than if they were absent ; they will not, however, increase 

 the stability more than if they were inside, and even in that 

 case they could not make the arrangement stable. Thus A 

 cannot hold a second atom of the type B, so that the com- 

 pound AB 2 is impossible, while that represented by AB is 

 saturated. Thus, if B be taken as the type of a monovalent 

 atom, A with its seven electrons would act like a monovalent 

 atom and would thus conform in this respect to the behaviour 

 of Fl. The electrons in the molecule are thus arranged in a 

 cell containing 8 electrons and surrounding the core of the 

 fluorine atom. Next, suppose that A instead of having 

 7 electrons in the outer layer has only 6, and let an atom B 

 get attached to it in the way we have supposed. This will 

 raise the number of electrons in the layer round A to seven ; 

 it can attach another atom before the number of electrons in 

 the outer layer is raised to 8, and the limit of stability 



2 M 2 



