1. The problem statement, all variables and given/known data State whether ionization is an endothermic or an exothermic process. 3. The attempt at a solution I know what exothermic and endothermic mean, and I know that the answer is that ionization of sodium is an endothermic process, but I don't know why and I'm hoping someone can explain it to me? What's going on that requires energy to be absorbed during the reaction? Thanks in advance.