Interionic coulombic electrostatic interactions,

The first is that hydration, or solvent structure-based interactions, is also to some extent of an electrostatic nature. For example, they involve interactions of ions with water dipoles and quadrupoles. Complex formation and chemical bond formation also involve electrical contributions. The difference with interionic coulomb forces between free ions is that this second category is typically short range. However, for the sake of argument, we shall heed the usual, but sloppy, distinction between electrical and chemical forces where the first category stands for the long-range coulombic interactions between free ions and the latter is... 

EXAMPLE 20.2 Why are sodium chloride crystals stable Let s assume that a crystal of sodium chloride is composed of hard spherical ions that interact solely through electrostatics. To compute the total energy, we sum all the pairwise coulombic interaction energies of one ion with every other ion in the crystal. Crystalline NaCl is arranged in a simple cubic lattice, with interionic spacings a = 2.81 A at 25 °C. 

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