﻿Elements of the Higher Groups. 1131 



one electron * only. Let us take the case of electrolytic 

 solutions. Here the electrical forces net equally strongly from 

 all directions, and a calcium atom loses both electrons. The 

 inner electrons being more solidly fixed to the nucleus do 

 not get detached. A sodium atom, on. the other hand, loses 

 under the same conditions only one electron, because there is 

 only one electron which can be torn off by the same agency 

 from a Na-atom. 



This proves that in the normal case both the valency 

 electrons in Ca occupy nearly identical positions in the 

 atomic system — they are contained in the same part of the 

 atomic volume, and are fixed to the system with forces which 

 are either identical or very nearly identical. 



Let us now consider what will take place when a Na-atom 

 and a Ca-atom are subjected to the same ionizing agencies, 

 say bombarding electrons, light pulses, or thermal collisions. 

 For the sake of simplicity we consider the first case only. 

 We shoot at a Ca- and at a Na-atom with the same number 

 of electrons, which are possessed of such energy that they 

 can tear off just one outer electron when it hits at the right 

 place in the atom. Now, assuming the atomic volumes to be 

 the same and the LP. to be the same, it is clear that the 

 number of successful hits on a Ca-atom will be twice as 

 great as the number of successful hits on a Na-atom, for in 

 the outer volume calcium has two electrons, while sodium 

 lias only one. In other words, for the same strength of the 

 ionizing agent, Ca-gas will be, roughly speaking, twice as 

 highly ionized as Na-gas. 



These considerations may be extended to all cases where 

 ionization takes place by encounter, either with a light 

 pulse or another atom. 



In support of this view, an interesting observation by 

 Millikan f may be cited here. Helium has two electrons 

 which, according to Bohr and Lande |, are both in the same 

 part of the atomic volume. Millikan finds that when helium 

 gas is bombarded by a-particles, then, in one case out of 

 seven, both electrons are simultaneously carried off' by the a- 

 particle. This could not take place if one electron was much 

 nearer the nucleus than the other, and was attached to the 

 nucleus with a greater force. If they are contained in the 

 same part of the atomic volume, then, according to the laws 

 of probability, in one case out of' eight, both electrons would 



* The strength of the ionizing agent is assumed to be not so large as 

 to be able to tear off any one of the inner electrons. 

 t Millikan and Wilkins, Phvs. lie v., March 1922. 

 I ZeiUchrift fin- Physik, Bd. i\. p. 33. 



4 D 2 



