(a) For the sodium chloride molecule (NaC1) discussed at the beginning of Section 42.1, what is the maximum separation of the ions for stability if they may be regarded as point charges? That is, what is the largest separation for which the energy of an Na+ ion and a C1– ion, calculated in this model, is lower than the energy of the two separate atoms Na and C1?
(b) Calculate this distance for the potassium bromide molecule, described in Exercise42.2.