WYCKOFF: FORCES BETWEEN ATOMS IN SOLIDS 579 



individual molecules to stick together are the electrical doublets. 

 The greater their moments the more important will be their 

 effect upon neighboring atoms. Consequently polar compounds 

 tend to be strongly aggregated. Nearly all such compounds 

 are solids at ordinary temperatures. The lower the temper- 

 ature the less the repulsion and the more the particles cling 

 together. At a sufficiently low temperature, the absolute zero, 

 a substance possessing even the smallest outside fields would 

 be a solid simply because the heat motion of the atoms, and 

 consequently their repulsion, vanishes. 



The effect of the intensity of combination is complicated. 

 If the bonding forces in the gas molecule of a particular com- 

 pound are so large and the residual forces so small that the 

 molecule remains a definite entity in the liquid and solid states, 

 it will in general be true that the greater the bonding forces, 

 the more bound-in will be the fields and the less will be the 

 degree of condensation. If, on the other hand, we have a com- 

 pound in which the molecule as we ordinarily understand it 

 disappears in the condensed states, and the entire portion under 

 consideration appears as one large molecule, it would seem to 

 be true that the more intense the bonding the more condensed 

 is the system. 



Formation of molecules in non-polar substances. — At room tem- 

 perature the molecule of chlorine is diatomic. The chlorine 

 atom possesses seven outside electrons and the tendency to pick 

 up one more and close the cluster is considerably greater than 

 the repellent eft'ect of the heat vibrations. The molecule can 

 be represented somewhat as follows:^- 



:®r®: 



• • « • 



'- There is a certain interest and importance attached to the representation of com- 

 pounds by the use of graphical formulas. The conventions in common use do not 

 indicate the nature of the forces between atoms. The representation, by G. N. 

 Lewis (op. cit.), of the distribution of the outside electrons between the atoms in 

 chemical compounds is a distinct advance in the writing of graphical formulas. 

 But his method has certain disadvantages. It is often tedious and, moreover, 

 unless considerable space is devoted to the formula, it does not show the positions 



