Cohesive energies of CsCl structure type crystals

The cohesive energies at room temperature on the Born model are calculated for the halides of caesium, thallium and ammonium having the CsCl structure. The results are compared with the experimental values, indicating good agreement for the caesium salts, reduced covalent binding for the thallous salts and suggesting a probable value for the proton affinity of ammonia (8.72 eV), based on the estimate of hydrogen-bonding contribution by Vetchinkin et al. (1959).