EADIUM, ATOMIC ENERGY, AND ATOMIC STRUCTURE 555 



trons held in common so impartially that they will not tend, to 

 some (albeit very small) extent, to pass over to one atom rather 

 than to the other. In the same way, in no polar compound has 

 the electron passed from one atom to another completely; the at- 

 tractive forces between the two atoms, tending to restore it to its 

 original position, must induce some distortion of the cubical ar- 

 rangement. 



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Atomic Structure and Chemical Affinity. In cases where 

 combination between two elements produces a molecule (e.g., 

 LiF) in which the arrangement of electrons is much more stable 

 than in the original substances, we shall clearly obtain a con- 

 siderable diminution in the internal energy of the system (see p. 

 160) as the result of the interaction. Chemical activity or affinity 

 hence appears to depend, finally, upon atomic structure. Where 

 the electron arrangement is extremely stable, as with the inert 

 gases, the element will be inert. Where electrons are readily 

 gained or lost, as with the halogens or the alkali metals, the ele- 

 ment will be active, and will form very stable compounds with 

 such elements as assist most readily in the interchange. 



Chemistry " within the atom " is still in its infancy, but it 

 cannot be doubted that its development will lead to results of 

 the greatest importance in the near future. The facts presented 

 in this volume were almost all derived on a purely experimental 

 basis, and the construction of hypotheses to correlate and explain 

 these facts has been a long and painful process. On the basis of 

 atomic structure, however, the next generation of chemists will 

 be able to predict physical and chemical properties in advance. 

 A multitude of new facts will thus be brought to light, and many 

 new applications of chemistry to industry will become evident. 



Exercises. 1. What justification has been obtained in this 

 chapter for the use of = 16 rather than H = 1 as a basis for 

 atomic weights? 



