text: is the bond enthalpy (of F2).  The coefficient 1/2 is used because the formation reaction is Li + 1/2 F2 → LiF.
  \mathit{IE}_M is the ionization energy of the metal atom: {M} + \mathit{IE}_{M} -> {M+} + e^-
  \mathit{EA}_X is the electron affinity of non-metal atom X (fluorine)
  is the lattice enthalpy (defined as exothermic here)
  The net enthalpy of formation and the first four of the five energies can be determined experimentally, but the lattice enthalpy cannot be measured directly.  Instead, the lattice enthalpy is calculated by subtracting the other four energies in the Born–Haber cycle from the net enthalpy of formation.
  A similar calculation applies for any metal other than lithium and/or any non-metal other than fluorine.
  The word cycle refers to the fact that one can also equate to zero the total enthalpy change for a cyclic process, starting and ending with LiF(s) in the example. This leads to
  which is equivalent to the previous equation.
  Formation of NaBr
  At ordinary temperatures, Na is solid and Br2 is liquid, so the enthalpy of vaporization of liquid bromine is added to the equation:
  In the above equation,  is the enthalpy of vaporization of Br2 at the temperature of interest (usually in kJ/mol).