Chem question? Potential energy?

How to calculate the potential energy between ions K + and I - ? The atomic radius of K + is 1.52, and for I - it is, 2.06. The equation that it said I should use is E = k(q1q2)/d, where distance is the sum of the ionic radii. The answers should be in KJ/mol. I did (8.998)(-1)(+1) / (1.52 + 2.06) and got an answer, then divided it by 1000 to get kJ. What am i doing wrong?? do i have to do something else because it's kj/mol??? please please help!! this is due in a couple of hours!!!