46 



L. VEGARD. 



.-N. Kl. 



Such a comparison would immediately show some striking similarities. 



For chemically related elements (7 constant) we find as a rule an 

 increase of atomic volume with increase of n in accordance with the 

 variation of a. This increase is in particular very marked for the ele- 

 ments Li, N'a, K, Eh, Cs and Mg, Ca, Sr, Ba. 



If, on the other hand, we consider the elements belonging to the 

 same period we find a marked difference between the variation of the 

 atomic volume and that of the radius. 



2 3 4 5 6 1 



A/amber of £I/ecf tons m Surface e Ring 



Fig 6. 



Let us e. g. consider the short period from iSe to Ar. These ele- 

 ments should have the same quantnumber of the surface ring; but the 

 number of electrons should increase from i (iVrt) te 7 (C/), and the radius 

 should decrease as shown in fig 6. Also the atomic volume curve shows 

 at first a rapid decrease; but it reaches a minimum at the element M 

 after which it increases quite rapidly to meet the most conspicuous 

 maximum at K. Taking one of the long periods we find a similar 

 variation of the atomic volume and, curiously enough, we find no se- 

 condary maximum for Cu and Ag as was to be expected. 



