the Molecule and Chemical Combination. 523> 



It is worthy of notice that in a case like one when 8 elec- 

 trons are distributed over a single layer and are on the verge 

 of instability, the readjustment of the electrons is prevented : 

 by another cause besides that of rigid arrangement. For 

 any readjustment of their positions would be accompanied by 

 a diminution in the minimum distance between two elec- 

 trons, but in the undisturbed state this minimum distance has 

 almost reached the limit consistent with stability ; thus an)' 

 rearrangement of the electrons will tend to be unstable and 

 to break up. Thus the system comprising the atom and its 

 electrons will not experience the attraction to which it would 

 be subject if the rearrangement of the electrons could be 

 maintained. 



The distance of the outer ring of electrons from the 

 centre of the atom will vary with the valency of the atom, 

 and can be calculated from the condition that the attraction 

 of the electron by the central charge balances its repulsion 

 by the other electrons in the ring. 



We have assumed that the attraction between a positive 



charge and an electron is of the form -^ 5 ; we must con- 



skier the expressions for a and b when there are negative 

 electrons as well as positive charges inside the outer ring- 

 Since the force between electrons varies rigorously as 1/r 2 , 

 the existence of these (inside the ring will not affect the term 

 b/r 3 in the expression for the attraction : this term will be 

 proportional to the positive charge, and therefore to the 

 atomic weight N. On the other hand, these electrons will 

 afreet the term air 1 : th^y will make a proportional to the 

 difference between the positive charge and the charge on the 

 electrons inside the outer ring ; but this difference in a 

 neutral atom is equal 'to the charge on the electrons in the 

 outer ring. Thus we may write the attractive force on an 

 electron in the outer layer in the form 



ne ~Ne . a 

 v r° 



where N is the atomic weight of the element anil n the 

 number of electrons in the outer ring, a is a constant. The 

 repulsion exerted by the other electrons in the outer layer is 



equal to S„/4?' 2 : where S»=2 — *, where 20 is the angle 



sin 6 



subtended at the centre of the atom by the line joining 



