The lattice energy of an ionic solid such as NaCl is the enthalpy change H° for the process in which the solid changes to ions.

The lattice energy of an ionic solid such as NaCl is the enthalpy change ˆ†H° for the process in which the solid changes to ions. For example,
NaCl(s) †’ Na+(g) + Cl(g) ˆ†H = 786 kJ/mol
Assume that the ionization energy and electron affinity are ˆ†H values for the processes defined by those terms. The ionization energy of Na is 496 kJ/mol. Use this, the electron affinity from Table 8.4, and the lattice energy of NaCl to calculate ˆ†H for the following process:
Na(g) + Cl(g) †’ NaCl(s)

Electron Affinities of the Main-Group Elements (kJ/mol) TABLE 8.4 IA IVA VIIA -73 -141 -328 Cl -349 -122 Al -53 -134 72 -200 Ga -120 -195 Te -190 -325 Rb -47 -101 -121 Pb -110 -295 -110 -180 -270 Atoms of the alkaline earth metals Group IIA) and the noble gases (Group VIIIA) do not form stable negative ions