Answer
See explanation.
Work Step by Step
a. $PE=\frac{1}{4 \pi \epsilon}\frac{(e)(-e)}{r}$
$ =-9.0\times10^9\frac{(1.6\times10^{-19} C)^2}{0.29\times10^{-9}m}=-7.95\times10^{-19}J=-5.0eV$
b. The binding energy of the molecule is the potential energy plus the ionization energy of K, minus the electron affinity of Br.
$$-5.0eV+4.3eV-3.5eV=-4.2 eV$$
We expect the actual binding energy to be somewhat smaller in magnitude than this estimate. The two ions are not point charges (they are “fuzzy”), and the potential energy is smaller in magnitude than what we estimated.
