Possibility of ionic crystals R⁺R^– 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 to evaluate the stability of such a form of Na in the NaC1 structure relative to normal metallic sodium. Evaluate the energy at the observed inter atomic distance in metallic sodium, and use 0.78eV as the electron affinity of Na.