the Molecule and Chemical Combination-. 



527 



whole of a large crystal as forming a single molecule. We 

 should naturally expect that when the atoms are crowded 

 together as in a solid, when each atom may come under the 

 influence of a large number of neighbours, the arrangement 

 of the electrons relatively to the atom may differ substantially 

 from that in a gaseous molecule. 



Let us now take the simplest type of molecule, that of an 

 elementary gas when the two atoms forming the molecule 

 are identical. For the union of two atoms each containing 

 one electron we have the arrangement represented in fig. 5, 

 where the positive charges AB and the electrons u ft are at 



Fiff. 5. 



the corners of a parallelogram. The angle of the parallelo- 

 gram will depend upon the law of force between two positive 



charges when separated by molecular distances. If e-(f>( -i 



is the attraction between unit positive charge and an electron 



at a distance r, e 2 yfr(-\ the repulsion between two positive 



charges at a distance r, then if Act (fig. 5) —r and the 

 angle Actft — Q we have for equilibrium 



cos — 



2* 2 </>( -\ sin = e^(2r sin 0). 



Thus we may regard the electrons in the atoms as a kind 

 of hook by which one atom gets coupled up with another ; this 

 disposition of electrons may be regarded as forming what is 

 called the " bond " by the chemists. Inasmuch as each bond 

 of this kind requires two electrons, the symbol, whether a 

 line or a dot, used by chemists to denote such a bond 

 represents two electrons ; if, as in my paper " Forces between 

 Atoms and Chemical Affinity, " I.e., we use two of these 

 symbols in place of one, the number of symbols will equal 



