You are tutoring a bright student in his last semester of introductory physics. The particular topic of the day is bonding in solids. When your session begins, the student hands you a slip of paper with the following equation printed on it: U, = -ak, 1 m He says that he found this equation in his online studying and that it is described as an expression for the ionic cohesive energy of a crystal formed by ionic bonding. He asks you to derive this equation.

You are tutoring a bright student in his last semester of introductory physics. The particular topic of the day is bonding in solids. When your session begins, the student hands you a slip of paper with the following equation printed on it: U, = -ak, 1 m He says that he found this equation in his online studying and that it is described as an expression for the ionic cohesive energy of a crystal formed by ionic bonding. He asks you to derive this equation.