the Molecule and Chemical Combination. 543 



For the scattering of light by the electrons in the 

 molecules of different gases, we should expect the arrange- 

 ment of the electrons in one shell to approach nearer to the 

 spherical symmetrical form than an arrangement in two, and 

 that two cells would approximate to the symmetrical more 

 closely than three; so that the ratio of the minimum to 

 the maximum intensity of the light would increase with the 

 number of cells. The following are Lord Rayleigh's deter- 

 minations of this ratio for several gases : — 



Gas. Ratio expressed as a percentage. 



Argon .... *46 



Hydrogen .... 3*83 



Nitrogen .... 4*06 



Oxygen .... 9*4 



Carbon dioxide . . 11*7 



Nitrous oxide . . . 15*4 

 We see how small this ratio is in the case of the sym- 

 metrical distribution of electrons round the argon atom, but 

 the most striking feature of the table is the great jump 

 between nitrogen and oxygen ; this is just what we should 

 expect on our view of the constitution of these molecules, as 

 the oxygen molecule contains two cells while the nitrogen 

 only has one. The carbon dioxide and nitrous oxide mole- 

 cules are 3-celled molecules, and we should expect them to 

 have a higher value than the 2-celled molecule oxygen. 



The measurement of this ratio promises to be a very 

 valuable aid in determining the configuration of the molecule : 

 it would, for example, be very interesting to know what is 

 the effect of replacing one or more of the hydrogen atoms in 

 CH 4 by halogens, and to compare its value for OH 4 , C 2 H 2 , 

 2 H 4 , and C 2 H 6 ; the first and second of these are one-celled 

 molecules, while the third and fourth have two cells. 



In one sense even the octet is not fully saturated, for 

 though it cannot receive any more electrons its own electrons 

 may serve, as it were, as party walls against which the 

 electrons round other atoms may fill up their gaps and become 

 octets ; thus, for example, one of the electrons in an octet 

 might complete the tale of 8 for a 7-electron chlorine atom. 

 This might come about as follows : — We know from experi- 

 ments on positive rays that the chlorine atom when moving 

 through a gas seizes and retains an electron torn from one 

 of the molecules of the gas. In the positive rays the chlorine 

 atoms are moving at a high speed, and have therefore great 

 energy ; this enables them to drag the electrons they grip 

 out of the molecules. If, however, they have less than a 

 critical amount of energy they will not be able to tear off the 

 electron ; this will grip them, and the chlorine atom will 

 become the prisoner of the molecule. 



