Imagine a crystal that exploits for binding the Coulomb attraction of the positive and negative ions of the same atom or molecule R. This is believed to occur with certain organic molecules, but it is not found when R is a single atom. Use the data in Tables 5 and 6 in Kittel to evaluate the stability of such a form of Na in the NaCl structure, relative to the normal metallic Na. Evaluate the energy at the observed interatomic distance in metallic Na, and use 0.78 eV as the electron affinity of Na.