## Chemistry: A Molecular Approach (3rd Edition)

This large difference is because $BaO$ has a much higher ion charge than $CsF$.
Lattice energy depends on the product of ion charges. $BaO$ is made up of $Ba^{2+}$ and $O^{2-}$ ions, and has the product of ion charges = -4. $CsF$ is made up of $Cs^+$ and $F^-$ ions, and its product of ionic charges is -1, which is four times less than that of $BaO$. So, its lattice energy is also around 4 times less than of $BaO$