530 Sir J. J. Thomson on the Structure of 



of the seven-electron atom w r ould ceteris paribus come apart 

 more easily than those of six-electron atoms. Thus we 

 should expect substances with a seven-electron atom like 

 chlorine to be more easily dissociated and mote energetic 

 in their action than those like oxygen, whose atom only 

 contains 6 electrons. 



We can apply similar considerations to the union of atoms 

 of two dissimilar elements, and we shall take as our text the 

 molecule of carbon monoxide. This substance has excited a 

 good deal of attention, as though from the valency point of 

 view it is highly unsaturated, its physical properties, for 

 example the difficulty with which it is liquefied, indicate 

 than its molecules exer6ise even less than the normal attrac- 

 tion upon each other. We know from experiments on the 

 Positive Rays that non-permanent molecules can be formed 

 which violate all principles of valency. Thus, when these 

 rays go through such a gas as C0C1 2 we get evidence of the 

 existence of all kinds of combinations of carbon and chlorine 

 atoms. Where valency comes in is in connexion with the 

 duration of -the compound after it has been formed. 



A molecule built up in conformity with valency principles 

 is one which, as we have seen, is not likely to attract or be 

 attracted by other molecules as much as one that is not made 

 up on these lines. The principle of valency depends in fact 

 upon the '* survival of the unattractive" ; attractive molecules 

 die young. If we can secure this unattractiveness by other 

 than valency conditions there is no reason why the compound 

 should not be as permanent as the orthodox one. Now let 

 us consider the case of CO. Here we have 10 electrons to 

 dispose of, the same as for N 2 , and we might expect that 

 a somewhat similiar arrangement to that shown in fig. 9 

 would produce a stable and permanent molecule. As the 

 positive charge on the carbon atom is not the same as that 

 on the oxygen, the cell will be distorted and will not be 

 symmetrical about the plane through the middle point of the 

 line joining C and 0. It is interesting to notice that some of 

 the physical properties of CO and N 2 are very similar. Thus, 

 if a and b are the constants for these gases in Van der Waals' 

 equation, b being what is called the atomic volume and a a 

 constant which i^ connected with the magnitude of the force 

 which one molecule exerts upon another, — then (Kaye and 

 Laby's Tables) : 



a. b. 



for CO '00275 -00168 



N 2 -00259 -00165 



