

ELECTRONS 81 



The other urge, instead of depending as does the first 

 upon the mutual attraction of protons and electrons, 

 depends upon the mutual repulsions which occur be- 

 tween two or more protons or between two or more 

 electrons. In any grouping of several protons and 

 electrons there are some amenities in the way of proper 

 separations between mutually repellent members. Cer- 

 tain configurations, or arrangements of the particles in 

 space, seem to be more stable than others and toward 

 such configurations this second urge is effective. 



One of the most stable groups comprises four protons 

 and four electrons, satisfying thereby the more funda- 

 mental urge of equal numbers. All of these, except two 

 electrons, are closely grouped into a tiny particle, known 

 as an "alpha particle." Why and how four protons 

 and two electrons should group so closely no one as yet 

 knows. (Perhaps, at such infinitely small and sub- 

 atomic distances, it has been suggested, the laws of 

 attraction and repulsion do not follow the same mathe- 

 matical relationship as they do for the larger distances 

 at which they were determined.) The two remaining 

 electrons disport themselves at some distance and 

 presumably on opposite sides of the alpha particle, which 

 attracts them because it has an excess of protons. 



The entire group is known as an atom of helium, that 

 inert gas which has been recommended for airships. 

 In this grouping both urges find complete satisfaction. 

 No greater satisfaction could be obtained by any ar- 

 rangement; so there is no residual tendency to join with 

 other protons and electrons to form a larger but more 

 stable group. 



