﻿294 Prof. A. 0. Rankine on the Molecular Structure 



molecule as having nearly the same dimensions as a neon 

 atom, and each sulphur atom in combination as approxi- 

 mating to the dimensions of an atom of argon. 



5. The remaining question of how far apart are the nuclei 

 of the atoms in the molecule finds a satisfactory answer in 

 the work of W. L. Bragg*, whose X-ray -crystal measure- 

 ments have enabled him to assign probable values for the 

 radii of the outer electron shells of the atoms of the inert 

 gases. The only values with which we are at the moment 

 concerned are those of neon o and argon, which are given 

 respectively as 0*65 and 1*03 Angstrom units. In cases like 

 those under consideration, where outer electrons are playing 

 a double part, the sharing is equivalent to contiguity of the 

 outer shells, so that the distance apart of the nuclei is the 

 sum of the radii of the appropriate inert atom shells. Thus 

 for C0 2 , which is pictured as three neon atoms in line, the 

 three nuclei are equally spaced and separated by distances 

 equal to twice the radius of the neon outer shell, i. e. 

 2x0-65 A = 1'30 A. In COS the distance between the 

 carbon and oxygen nuclei is the same, namely 1*30 A, 

 but the distance between the carbon and sulphur nuclei 

 is the sum of the radii of the outer electron shells of 



O Q O 



the neon and argon atoms, i. e. 0*65 A-f 1*03 A = 1*68 A. 

 The three nuclei in COS are thus unequally spaced on 

 account of the greater size of the argon atom. In CS 2 the 

 distance between the o carbon nucleus and each sulphur 

 nucleus is also 1*68 A, and the three nuclei are again 

 spaced symmetrically. 



6. It is evident that none of the three molecules under 

 consideration, if their configurations are as indicated, can be 

 expected to display spherical symmetry. In these circum- 

 stances it is necessary to interpret in a special way the 

 results of the well recognized method of calculating 

 molecular dimensions from viscosity data. The quantity 

 which is actually derivable from the formula is the mean 

 value of the area which the molecule presents, for all 

 possible orientations, as a target for mutual collision with 

 other molecules in the gas. This area the author f has 

 ventured to call the mean collision area, and its value for 

 COS is given by C. J. Smith (loc. cit.) as 1*06 x lO" 15 cm. 2 

 The immediate problem before us is to find how nearly the 

 tentative model of this molecule described above would 

 exhibit this value for its mean collision area. The values of 



* W. L. Brag-o-, Phil. Mag. vol. xl. p. 169. 



| A. O. Kankine, Proc. Eov. Soc. A, vol. xcviii. p. 360, and Proc. 

 Phys. Soc. vol. xxxiii. p. 362. 



