Here's my understanding of the Force /Separation graph, I'm open to criticism/ridicule if I've got it wrong: If the two atoms are pushed together, then there is a repulsive force between them of a positive magnitude. If they are separated by a distance r, then the two forces (repulsive/attractive) are equal but opposite and the atoms are in a state of equilibrium. At a separation greater than r, the force is that of attraction, and if the separation is greater than 2r, then the attraction tends to zero. Potential Energy/Separation: If the two atoms are separated by an infinite distance, then there is no attraction between them, and there is no Potential Energy. But as they come closer together, Potential Energy decrease until at a distance of r, potential energy is at a minimum. If the separation is reduced further, the line of Potential Energy passes through zero. Why is the potential energy zero? What actually happens to the 2 atoms when the potential energy becomes zero? I'm confused, can anyone clear this up for me please? Thanks.