I've seen electrostatic interaction energy (from $E\sim \frac{q_1 q_2}{r}$) used to explain differences in lattice enthalpies between different crystalline solids. For example, I've seen it explained that $\ce{NaF}$'s $\pu{910 kJ/mol}$ lattice enthalpy is less than $\ce{MgCl2}$'s $\pu{2326 kJ/mol}$ because of $\ce{Mg}$'s greater cationic charge (+2 vs. +1).

Question: Isn't the lattice enthalpy defined per stochiometric unit, rather than per nearest-neighbor interaction? And if so, if one is going to use electrostatic models of nearest-neighbor interaction to explain differences in lattice enthalpy, shouldn't the respective lattice enthalpies first be divided by the number of nearest-neighbor interactions per stochiometric unit?

  • $\begingroup$ What is "per bond"? There are no individual bonds here anyway. $\endgroup$ – Ivan Neretin May 19 at 1:40
  • $\begingroup$ @IvanNeretin Good point. I've edited my question. $\endgroup$ – theorist May 19 at 4:02

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