Question & Answer: The potential energy E per Cs^+ – Cl^- pair within the CsCl crystal depends on the interionic…..

The potential energy E per Cs^+ – Cl^- pair within the CsCl crystal depends on the interionic separation r in the same fashion as in the NaCl crystal. E(r) = -e^2 M/4 pi epsilon_0 r + B/r^m where for CsCl, M = 1.763, B = 1.192 times 10^-104 J m^9 or 7.442 times 10^-5 eV (nm)^9, and m = 9. Find the equilibrium separation (r_o) of the ions in the crystal and the ionic bonding energy, that is, the ionic cohesive energy, and compare the latter value to the experimental value of 657 kJ mol^-1. Given that the ionization energy of Cs is 3.89 eV and the electron affinity of Cl (energy released when an electron is added) is 3.61 eV, calculate the atomic cohesive energy of the CsCl crystal as joules per mole.