568 WYCKOFF: forces between atoms in solids 



must be rather weakly bound. The positive rays are atoms 

 which have lost a few electrons. Perhaps the strongest evidence, 

 at any rate from the point of view of the chemist, that atoms 

 possess a small number of loosely held electrons is furnished by 

 the phenomenon of electrolytic dissociation. Since the mag- 

 nitude of the electrical charges concerned is the same as that 

 of the charge on the electron, the conclusion can hardly be 

 avoided that a few electrons are involved. It is the natural 

 thing to identify them with the "dispersion electrons" already 

 mentioned. These outside rather weakly bound electrons are 

 the ones involved in chemical changes. 



Arrangement of electrons. — No real information is available 

 concerning the exact arrangement of the electrons in an atom. 

 These electrons must either be in motion about the nucleus 

 (the revolving-electron type) or else they must be held in equil- 

 ibrium positions about the center (the stationary-electron type). 

 There are serious difficulties in the way of either arrangement.^^ 

 Since the loosely bound electrons are the only ones involved in 

 chemical reactions, the exact arrangement of the inner elec- 

 trons is a matter of secondary importance to the chemist, at 

 least for the present. ^^ 



From the standpoint of the chemist the stationary-electron 

 atom seems simpler because its qualitative application is easier. 

 This application can be made with either type of atom, however, 

 and in the present state of our knowledge one is quite justified 

 in imagining and using for chemical purposes whichever type of 



'^ It may be of interest to chemists to restate the most obvious of these objec- 

 tions. If the electrons are in revolution about the nucleus and if light is an electro- 

 magnetic phenomenon, as it is firmly believed to be, then a continuous radiation 

 of energy from the atom as a result of this motion would be expected. In a com- 

 paratively short time the atom would "run down," disintegrate. This may or 

 may not be a fallacious argument. On the other hand, in the case of the station- 

 ary-electron atom, unless a hitherto unknown force of repulsion is assumed, it is 

 hard to see why the negatively charged electrons do not fall into the positively 

 charged nucleus and become neutralized. 



^* Also since chemical changes affect only the outside electrons, it is quite clear 

 that chemical facts can present only the most indirect information concerning the 

 inside electrons of an atom. 



