580 WYCKOFF: FORCES BETWEEN ATOMS IN SOLIDS 



each atom striving to claim an electron from the other. 

 This arrangement will quite completely close the fields about 

 the molecule as a whole and the diatomic chlorine molecule 

 (CI2) will possess relatively little residual affinity. As the 

 temperature is raised the increased energy results (i) in a 

 larger vibration of the atoms within the molecule, and (2) 

 more especially in the increased violence of the motion 

 of the molecule as a whole. Thus there will come a time 

 when some of the molecules will be traveling with so great 

 a speed that the violence of their collisions will be suffi- 

 cient to cause the splitting of the molecule. At this point we 

 begin to have monatomic chlorine. The number of simpler 

 molecules increases faster than the increase in temperature at a 

 rate depending upon the importance of factor (i). The ampli- 

 tudes of the atomic vibrations depend in an inverse ratio upon 

 their weights and the intensity of the bonding. It is to be ex- 

 pected that the dissociation of a weak compound under the 

 influence of heat will proceed at a faster rate than when the 

 union is strong. Increase in temperature raises the reactivity 

 because with larger intra-molecular vibrations the fields of force 



of the electrons. The pictures used by Lewis and adopted by Langmuir give, as 

 representations of space models, a truer idea of the actual state of affairs within 

 compounds, but, by reason of their complexity, are not in most cases sufficiently 

 useful to be practicable. 



It has been found useful to designate the mode of combination, where this added 

 information is of value, by the following modifications of the ordinary chemical 

 "bonds." The passage of an electron from one atom to another is shown by a 

 full-pointed arrow. Caesium chloride, in which the chlorine atom has captured 

 the outside electron of the caesium atom, is Cs > CI. The holding of an elec- 

 tron in an equilibrium position between two atoms, as in bromine vapor where 

 each bromine atom of the bromine molecule is striving to acquire one electron 

 from the other bromine atom, can be indicated by a half -pointed arrow pointing 

 in the direction of the displacement of the electron (as, Br ^ Br). If it is of 

 advantage to know the approximate amount of this displacement, which serves 

 of course as a measure of the doublet fields set up, this can be done by cutting the 



arrow with a dash at the approximate position of the electron. Thus .4 1 ^ B 



would mean that B was drawing one of ^'s electrons with a pull sufficient to 

 displace it to a position half the way towards B. 



The diagrams given in the text are a combination of this method of representa- 

 tion with the idea of showing the distribution of all the outside electrons. 



