342 Albert P. Mathews 



about 60 percent are open and 40 percent are closed, the 

 average valence being about 1.20; in neon, 16 percent are 

 open and 84 percent are closed, the average valence being 

 about 0.32; and in helium only about 5 percent of the valences 

 are open, 95 percent being closed, giving an average valence 

 of o.io. This explains, then, why the elements appear zero 

 valent in the periodic table, since they are zero valent as far 

 as their chief valences are concerned; why, nevertheless, they 

 appear to have some weak chemical affinity, and cohesion; 

 why they refract and disperse light; and also why the average 

 valence is fractional rather than being a whole number. 



It also explains more than this. It enables us to under- 

 stand the easy dissociation of the molecules into atoms. 

 Unlike atoms that are bound together into molecules by their 

 chief valences, no electrical stresses are set up in the argon 

 elements when dissociation into atoms occurs, because each 

 atom having a positive and a negative valence becomes at 

 once electrically neutral. It is well known that compounds 

 formed from residual valences partake of the nature of molec- 

 ular compounds and break up very easily. Neither their 

 union, nor their dissociation, involves much, if any, energy 

 exchange. Such compounds are often called, indeed, molec- 

 ular compounds. A double bond of this kind is always a 

 weak bond in any molecule, which easily breaks where the 

 double bond is. Were they univalent their dissociation into 

 atoms would be very hard to understand. 



I suppose we may picture the opening of these residual 

 valences in the manner suggested by Sir J. J. Thomson, as 

 being due to a rearrangement of the electrons within the 

 atom so that an excess of negative electricity is temporarily 

 produced in one spot, and of positive at another spot on the 

 surface of the atom. These excesses are the valences. 



In closing, it is not without interest to compare the 

 valence numbers computed above from the cohesion, with the 

 refractivity as determined by Cuthbertson. 1 Their re- 

 fractivities are in the proportion i, 2, 8, 12 and 19. 



1 Cuthbertson, C.: Phil. Trans., 204, 323 (1905). 



