WYCKOFF: FORCES BETWEEN ATOMS IN SOUDS 573 



We can thus account for the existence of a tendency to add 

 electrons beyond the number numerically equal to the charge 

 on the nucleus but we are unable to state why electrons will 

 add on to the atom to form clusters of eight rather than seven 

 or nine or some other number-- and why the formation of the 

 cluster of eight results in such a great condensation of the fields 

 of force about the atom. For our purposes the recognition of 

 this tendency is all that is necessary. 



Chemical valence. — Valence, then, might be defined simply as 

 the tendency for the electrical (and probably also the magnetic) '^ 

 fields to condense together to the greatest possible extent with 

 the possession of an outside cluster of eight (also sometimes a 

 cluster of two and sometimes a cluster of twice eight) electrons. 

 The repetition of properties after the addition of eight elec- 

 trons and the existence of a tendency to add electrons with 

 the formation of clusters of eight were recognized by J. J. Thom- 

 son;- they underlie the application of the "magneton" atom of 

 A. L. Parson*^ and the "cubical atom" of G. N. Lewis ;-^ and they 

 form the basis of what Langmuir' has chosen to call "the octet 

 theory of valence," which is simply the application of this un- 

 deniable tendency to the representation of chemical compounds.-^ 



Doublets. — Two electrical charges of opposite sign form a 

 dotiblet, the moment of which with respect to an outside point 

 (roughly, the effect of which upon an outside point) increases 

 as the distance apart of the poles becomes greater.'-^ Such doub- 



2^ Langtnuir's idea of cells suggests an explanation of this, but it must be borne 

 in mind that his work only gives a possible geometrical arrangement of points of 

 one kind about a point of a diffe^-ent kind and does not discuss how such a system 

 could be physically stable. If the only forces of attraction and repulsion acting 

 are those with which we are now familiar, such an atom model is unstable. As 

 long as this theory is used simply as a convenient aid in picturing the atom it may 

 prove useful to the chemist, but as yet no evidence has been presented to show 

 that this model represents the actual arrangement of the electrons in the atom. 



^3 As was earlier implied, these various discussions are not setting up new the- 

 ories of valence but are indicating the explanation which the knowledge of the 

 structure of the atom has to offer of the facts of valence as we have learned them. 



^^ A doublet of this sort can be conveniently pictured. The fields of force between 

 two electrical charges can be represented by lines (really tubes of force) passing 

 from one to the other. The number of the lines serves as a measure of the intensity 

 of the field. If the two charges are close together, the lines of force are for^the 



