Influence of Atomic Weight. 



317 



difference is 2. Now it is remarkable that this difference of 

 2 , instead of 3, for Li and ISTa likewise has its influence on the 

 properties of these elements and those belonging to the same 

 series ; for, as Mendeljeff has pointed out, his second series of 

 elements, containing Li, Be, 0, N, 0, and F, and part of his 

 third series, containing Na, Mg, Al, and Si, are apparent ex- 

 ceptions to his theory of odd and even series. Thus Na> 

 though belonging to the same subgroup, does not so much 

 resemble Cu, Ag, and Au as theiatter resemble one another ; 

 and the same thing holds good for Mg, F, 0, N, C, &c. This 

 is rendered especially evident by the melting-points (see 

 Table on p. 315), and explains why N 0, F ?, Na, Mg, Al, and 

 Si have melting-points which are so very different from those 

 of the other members of their respective subgroups, and re- 

 semble more those of the other subgroup. 



(2) Another interesting numerical relation between the 

 atomic weights of the elements is that pointed out by Woechter 

 (Deut. cliem. Ges. Ber. xi. 11). This is represented in the 

 following Table : — 





a. 



a+(lxl6) 



CI =35-5 

 S =32 

 P =31 

 Si =28 

 Al =27-4 

 Mg=24 

 Na = 23 



a+(2xl6). 



a + (3x16). 



Univalent 



F =19 



=16 

 N =14 

 C =12 

 B =11 

 Be= 9-2 

 Li= 7 



Ca = 40 

 K =39-1 







Trivalent 



Quadrivalent... 

 Trivalent 



Univalent 



a+(4xl6). 



a-{-(5xl6). 



a + (6xl6). 



«+(7xl6). 



a+(8xl6). 



Br = 80 



Se =79 



As = 75 



76 



Yt = 89 

 Sr=87-5 

 Eb = 85-5 







I =127 

 Te = 128 



Sb=112 



Ce =140 

 Di =138 

 Ba=137 

 Cs =133 



This Table exhibits the following relations : — 



(a) The affinity of the elements diminishes from F to Si with 

 rising atomic weight and rising atomicity; and then from this point 

 up to Cs it increases with rising atomic iveight and falling atomicity. 



We have therefore F at the beginning and Cs at the end 

 of the series ; and these two elements have the strongest, but 

 opposite, affinities. The other elements have a smaller affi- 

 nity the nearer they stand to the middle of the series. This 

 middle point is marked in the Table by the number 76 in 

 large type. In other words, as we pass from F, the most ne- 

 gative of the elements, they tend to become less negative and 

 more positive till we reach Cs, the most positive of all. 



These statements are rendered evident by the following 

 Table (p. 318) (given by Woechter in the memoir referred to), 



