Arrange the compounds from highest lattice energy to lowest

Question

Arrange the compounds according to the magnitudes of their lattice energies based on the relative ion charges and sizes from highest lattice energy to lowest lattice energy.

NaF, MgO, KCl, MgF₂

Answer 1

Lattice energy will depend mainly on the charge on the ions and also on the size of the ions. The greater the charge and the smaller the ions, the greater will be the lattice energy. (See Coulomb's Law).

Both The Mg cation has 2+ charge so MgO and MgF₂ will have greater LE than NaF and KCl. Now to rank MgO and MgF₂, we put MgO first because O has a 2- charge compared to F which is 1-. So, we have

MgO > MgF₂. Next, we can look at NaF and KCl (all are 1+ and 1- charges) and we look at atomic radii.Na is smaller than K and F is smaller than Cl, so NaF will have a greater LE than KCl.

Final rank order would be:

MgO > MgF₂ > NaF > KCl