I'm had this class yesterday that I did'nt understand anything, I have exam on two days and I started to study by myself about potential energy so, I found this equation:
Ue(r) = q1 q2/4πε0r + repulsive energy (same as van der Waals)
where q1 = -q2 and each q = + or - 1.6E-19 C
and...