524 Sir J. J. Thomson on the Structure of 



2 electrons in the outer ring. Since the repulsion must 

 balance the attraction, we have 



ne N^ . a _ S w 



Na 

 or r — —- 



»-i 



For hydrogen N=w = l, S n = 0, so that ?' H = a ; 



for lithium N = 7, rc = l, S„ = 0, „ ?' Li =7a; 



for beryllium... N = 9, n = 2, Sn==l, ,? ?' Be =5"14a; 



for boron N = ll, w=3, S„=2'3, „ r B ==4*52« ; 



for carbon N=12, n = 4, S, 2 = 3'66, „ r Q = 3'88a; 



for nitrogen .'.. N==14, n=5, S«=5"2, „ r N = 3'78a; 



for oxygen N=16, n=6, S ?l =6*68, „ ?' =3*69 a; 



for fluorine ... N = 19, ra=7, S» = 8*08, ,, ?• =3*8a; 



for neon N = 20, w = 8, S M = 10'1, ,, r w =3'63a; 



Xe 



for sodium N = 23, « = 1, S» = 0, ,, »\* =23 



Xa 



a 



Thus, taking the elements from lithium to neon, we see that 

 the radius of the outer layer is greatest for. the lightest 

 element and diminishes rapidly at first and then very slowly 

 to the end of the series ; when we pass from neon, the last 

 element in this period, to sodium the first in the next, there 

 is a great increase in the radius : this increase is again 

 followed by a diminution which continues until we reach 

 argon ; when we pass to potassium, the first element in the 

 next series, there is again a large increase. The radii of 

 the layers in the same group like lithium, sodium, potassium, 

 fluorine, chlorine, bromine, increase with their atomic 

 weights. Thus the relation between the radii of the layers 

 and the atomic weight is represented on this theory by a 

 graph differing from the historic one for the atomic volumes 

 and atomic weight given by Lothar Meyer and reproduced 

 in almost every text-book of chemistry : here the minimum 

 atomic volume comes in the middle of a period and not at 

 the end. Recent investigations, however, have shown that 

 the relation between atomic volume and atomic weight is 

 not accurately represented by a curve of the type of that of 



