THE VALENCE OF CHLORINE AS DETERMINED FROM 



THE MOLECULAR COHESION OF CHLORINE 



COMPOUNDS 



BY ALBERT P. MATHEWS 



Since molecular cohesion is a function of the molecular 

 weight and the number of valences in the molecule, 1 we may 

 use the cohesion for the purpose of determining the valence 

 of elements; and in this paper I shall consider chlorine, although 

 something will be said, also, about the other halogens. 



It is generally believed, at the present time, that the 

 valence of chlorine is not fixed, but varies in different com- 

 pounds from one to seven. In its organic, and some inor- 

 ganic compounds, and in its elemental form it is generally 

 represented as univalent; whereas in the chlorates it is sup- 

 posed to be pentavalent; and in the perchlorates it is hepta- 

 valent. 



That chlorine even in such compounds as chloroform, 

 where it replaces univalent hydrogen, may not be univalent 

 is indicated by the action of chlorine compounds on light. 

 Drude, 2 reasoning that it must be the valence electrons of 

 compounds which would have a period of vibration sufficiently 

 long to respond to light waves, worked out a modification 

 of the Ketteler-Helmholtz dispersion formula which enabled 

 an approximate computation of the number of electrons in- 

 fluencing dispersion in the molecule. He found that in 

 many cases this number was close to the total number of 

 valences in the molecule; but in the case of compounds con- 

 taining chlorine and fluorine, the number of such light-re- 

 fracting valences was always greater than in the correspond- 

 ing hydrogen compounds, and he inferred from this that 



1 Mathews: "The Relation of the Constant "a" of van der Waals' Equa- 

 tion to the Molecular Weight and the Number of Valences in the Molecule," 

 Jour. Phys. Chem., 17, 181 (1913). 



2 Drude: "Optische Eigenschaften und Elektronen Theorie," Annalen der 

 Physik, [4], 14, 677 (1904). 



