Question

Place the following in order of increasing magnitude of lattice energy. MgO LiI Ba S

Answer 1

As the charges on the ions increase the lattice energy increases (becomes more negative),

when ions are closer together the lattice energy increases (becomes more negative)

To decide whether BaS or MgO(as both in same group) has the greater lattice energy, we need to consider the relative sizes of the ions because both compounds contain a +2 metal ion and a −2 chalcogenide ion. Because Ba2+ lies below Mg2+ in the periodic table, Ba2+ is larger than Mg2+. Similarly, S2− is larger than O2−. Because the cation and the anion in BaS are both larger than the corresponding ions in MgO, the internuclear distance is greater in BaS and its lattice energy will be lower than that of MgO. LiI is having +1 charge so its lattice energy lesser than MgO and BaS.

Here the decreasing order of lattice energy MgO >BaS>LiI