438 



FOOTE AND MOHLER: IONIZATION 



sidered as representing the work required to first sublime a mol 

 of crystal and then ionize each molecule by dissociation. Or, 

 in terms of thermochemical data, it represents the heat of forma- 

 tion of a mol of the salt, plus the heat of dissociation of one-half 

 mol of halogen gas, plus the heat of sublimation of a mol of metal, 

 plus the work of ionization of a mol of metal, minus the work 

 represented in the electron affinity of a gram atom of halogen 

 gas; the end products of either transition being identical. 



Accordingly equation (2) may be expressed in the following 

 general form: 



UiRx] = J(Rx) + 5[Rx] = 0[Rx] + S[R] + D(x) - E(x) + /(R) (3) 



Table i gives the values of the grating energies computed by 

 Born, from which the ionization potentials may be obtained di- 

 rectly if the heat of sublimation of the salt were known : 



TABLE 1 

 Born's Values of Grating Energies 



The numbers in this table are expressed in kilogram calories 

 per mol. Equation (4) gives the relation between kilogram 

 calories per mol and potential in volts. 



kilogram calories per mol = 23 . i X volts (4) 



Halides of the second group. — The ionization of vapors of these 

 halides may be very much more complicated than those of the 

 alkali halides because of the higher valence of the metal. The 

 grating energies of the salts have not been determined. As a 

 particular example of the possible conditions to be expected, we 

 shall consider the ionization of mercuric and mercurous chlorides. 



The mercuric chloride molecule consists of a doubly posi- 

 tively charged mercury atom and two negatively charged chlorine' 

 atoms. Ionization may result in the following immediate con- 

 ditions : 



