582 fwYCKOFF: FORCES BETWEEN ATOMS IN SOUDS 



to complete the clusters are not nearly so great as the tenacity 

 with which hydrogen and carbon retain electrons. The elec- 

 trons consequently are not appreciably displaced from their 

 equilibrium positions. The stray fields are relatively small and 

 the gas liquefies at a rather low temperature. The chemical 

 molecules preserve their identity in the liquid and solid states, 

 being held to one another by the relatively slight secondary 

 attraction. 



Carbon compounds in general are characterized by great 

 stability, due to the intensity with which carbon clings to its 

 electrons, and by the smallness of the residual attractions pos- 

 sessed by the molecules of such compounds. In passing hor- 

 izontally along the periodic table, when carbon is reached the 

 tendency to add electrons with the formation of a stable cluster 

 is not as yet so great that carbon is able to capture electrons 

 from other atoms, and consequently there are no doublets of 

 large moment. The properties of organic compounds in general 

 force the conclusion that in the solid and liquid states the chem- 

 ical molecule remains just as definite an entity as in the vapor. 

 Practically all but the simplest compounds are solids or liquids, 

 in spite of the weakness of the residual forces, because such large 

 molecules require a considerable amount of heat energy to pro- 

 duce even a small displacement.^^ Certain kinds of organic 

 compounds, such as the alcohols, acids, and nitro- and nitrile- 

 compounds, are more associated than would be expected. This 

 is due to their possessing doublets of considerable moment.^ 



Formation of molecules in polar substances. — With compounds 

 of the polar type the mechanism is quite different. The ten- 

 dency of chlorine to acquire one electron is so great and the 

 holding power of sodium for the one outside electron is so weak 

 that in a molecule of sodium chloride vapor the electron may 

 be considered to have gone over most of the way to the chlorine. 

 A molecule of sodium chloride vapor may be represented thus: 



®^:© 



^^ Information from the specific heats and from the variations in the specific 

 heat with temperature should be of interest in this connection. 



