592 WYCKOFF: FORCES BETWEEN ATOMS IN SOLIDS 



to silver cyanide is typical. Silver cyanide possesses a structure 

 similar to silver iodide. The cyanide ion is less strongly negative 

 than the iodide ion, the electron is nearer the silver atom and 

 consequently the doublet is of less moment. The fields within 

 the silver cyanide molecule are quite intense. When the solid 

 is placed in a solution of potassium cyanide, the cyanide ions 

 will become by collision imbedded within these drawn-in fields 

 between the silver atom and the cyanide radical. This addi- 

 tional cyanide ion will so increase the resulting doublet fields 

 that the water molecules are able to cause solution by reason of 

 the interaction of their fields with those of the new silver cyanide 

 anion in the solid. 



In future papers it is planned to discuss in detail the informa- 

 tion which X-ray determinations of the structure of crystals, 

 infra-red spectra measurements, and specific heat measurements 

 offer concerning the nature of the forces between the atoms in 

 solids, and to present the results of X-ray studies of various 

 typical crystals. 



SUMMARY 



1. The structure of the atom, as we now know it, is discussed 

 with reference to the nature of the forces operating between 

 atoms, and it is emphasized that only the arrangement of the 

 outside electrons has a bearing on the phenomena usually in- 

 cluded under the term "chemistry." The arrangement of the 

 inner electrons cannot be deduced from chemical data alone. 

 The outstanding fact is the tendency, still unexplained, to form 

 "closed clusters" of eight or twice-eight electrons. 



2. Several typical compounds are considered with reference 

 to the nature of the forces producing them. All compounds lie 

 between the two extremes of "polar" and "non-polar" com- 

 pounds. A simplified method of representing the type of com- 

 bination in a given compound is suggested. 



3. Solid substances are classified, according to the nature of 

 the forces of combination, into molecule-forming, polar, and 

 valency compounds. 



4. The phenomena of adsorption, solubility, ionization in solu- 

 tion, formation of complex ions, and molecular complexes are 

 discussed from this point of view. 



