578 WYCKOFF: forces between atoms in solids 



A non-polar compound is held together by the entangling of 

 the fields of force about the constituent atoms. No electron 

 transfer occurs. Each atom may be considered as drawing 

 electrons from another in the endeavor to complete a stable 

 group. In such a union as this, one unit of valence is equivalent 

 to two "free" chemical "links," that is, one chemical "bond" in 

 the compound. ^° Such a non-polar compound would of course 

 have to be formed between atoms which held their electrons 

 with about equal intensity. 



All gradations between these two extremes probably occur 

 where the bonding electrons, taking up positions between the 

 two atoms, may be thought of as belonging to both. Most 

 compounds, especially in the vapor state, must lie in this inter- 

 mediate class. A given compound is not necessarily polar or 

 non-polar in all its states of aggregation; it may shift from one 

 class toward the other. In the solid and liquid states the close 

 proximity of other atoms has a strong influence upon the prop- 

 erties of a molecule.^^ 



States of aggregation. — When the total attractive forces be- 

 tween the units (molecules) of a substance is less than the repel- 

 lent forces of thermal agitation, the molecules will part from 

 one another and the substance is said to be in the gaseous state. 

 The less the attractive force compared with the thermal agitation, 

 the more "perfect" will be the gas. A liquid results when these 

 residual fields (stray doublet fields) just exceed the effects of 

 the heat vibrations. When the fields become relatively very 

 large and the atoms are able to take up definite positions, the 

 substance solidifies. Of greatest importance in causing the 



8" J. J. Thomson (op. cit.) has indicated this fact. Using the idea of Faraday 

 tubes of force, as he does, we would say that unless a cluster of eight is formed 

 the valency electron, to be fixed in position, requires that it shall have tubes of 

 force running to two atoms, one other besides the one to which it belongs. This 

 will be quite evident when typical cases, chlorine and methane, have been con- 

 sidered. 



2 1 When molecules approach one another, there will be an interlocking of their 

 stray fields. A certain weakening of the fields of the molecule itself will result. 

 With doublets of large moment, where the separation of the charges is great, the 

 fields will be spread out and the interlocking may be of marked effect upon the 

 molecule. 



