1. The problem statement, all variables and given/known data The potential energy of a pair of hydrogen atoms separated by a large distance x is given by U(x)= -C6/x^6, where C6 is a positive constant. What is the force that one atom exerts on the other? Is this force attractive or repulsive? 2. Relevant equations 3. The attempt at a solution I'm thinking we have to take the derivative of the equation??