1. The problem statement, all variables and given/known data Calculate the (electrostatic) force between a Ca2+ and an O2– ion the centers of which are separated by a distance of 1.25 nm. 2. Relevant equations I know that: Coulomb's Law is F = (k q1 q2)/r2 Attractive Force is F = (k z1e z2e)/r2 where z1 and z2 are the valence electrons, and e is the charge of an electron. 3. The attempt at a solution The textbook problem asks for the attractive force, so: F = [ (9 x 109)(2)(2)(1.6 x 10-19)2 ] / (1.25 x 10-9)2 Which is 5.89 x 10-10 N That's the correct answer to the attractive force, but the question my instructor has posed is to find the electrostatic force. I'm unsure what the difference between the attractive force and electrostatic force is. Would I just calculate it using Coulomb's Law without taking into account the valence electrons? Thanks in advance!