336 Atomic Structure from Physico- Chemical Standpoint, 



atom o£ radium-B do actually attain speeds of this order of 

 magnitude; for it has been found that the /3-rays from 

 radium-B travel at velocities ranging between 0"36 and 0*70, 

 when the speed of light is taken as unity. The value 0*64, 

 calculated from purely theoretical considerations, certainly 

 agrees closely with what is actually established with regard 

 to those electronic velocities with which we are acquainted. 



The velocity hypothesis furnishes an explanation of the 

 case of the isotopic elements which, up to the present, have 

 presented an unsolved problem. If it be assumed that in two 

 isotopes the internal mechanism of the atoms is identical in 

 every way, then the chemical inseparability of the two 

 elements can be explained ; and if it be further assumed that 

 the intra-atomic velocities are different, then the masses of 

 the two systems will also differ; all of which is exactly what 

 is found in practice. 



Further, a point of some interest arises when the Geiger- 

 Nuttall relation is considered in this connexion . This empirical 

 relationship establishes the fact that atoms throughout their 

 various stages of disintegration still preserve a feature which 

 is characteristic of their origin. This common characteristic 

 pervades each of the three radioactive series and differentiates 

 its members from those of the other series. It cannot be a 

 chemical factor, for the elements belonging to the same 

 series differ widely from each other in chemical character. 

 It seems not unreasonable to suppose, however, that throughout 

 the changes which the radio-elements undergo, one or more 

 of the orbits within the atom remain unaffected by the 

 process ; and that the velocity of the electrons in these 

 orbits may be the " distinctive feature " which survives the 

 catastrophe of atomic disintegration. 



The foregoing is sufficient to show that the suggested model 

 atom meets the demands made upon it from the chemical 

 side; and to this extent it justifies further consideration. 

 An examination of it from the physical standpoint would be 

 of interest. In the meantime, it may be pointed out once 

 more that this view of atomic structure is to be regarded as 

 suggestive rather than constructive. 



The Physical Chemistry Department, 

 The University of Glasgow. 



