Question

Arrange the following substances according to their expected lattice energies, listing them from highest lattice energy to the lowest: MgS, KI, GaN LiBr

Answer 1

Lattice energies are governed by two factors - the magnitude of the charges and the size of the ions. In general, the greater the charges involved, and the smaller the atoms involved, the higher the lattice energy. The effects of charge generally outweigh the effects of size.

The charges involved are:

MgS: +/- 2
KI: +/- 1
GaN: +/- 3
LiBr: +/- 1

Thus GaN has the highest lattice energy, followed by MgS.

Now, both atoms in KI are larger than the corresponding atoms in LiBr, so LiBr > KI. So the final ordering is:

(highest lattice energy) GaN > MgS > LiBr > KI (lowest lattice energy).

Answer 2

Lattice energies are governed by two factors - the magnitude of the charges and the size of the ions. In general, the greater the charges involved, and the smaller the atoms involved, the higher the lattice energy. The effects of charge generally outweigh the effects of size.

The charges involved are:

MgS: +/- 2
KI: +/- 1
GaN: +/- 3
LiBr: +/- 1

Thus GaN has the highest lattice energy, followed by MgS.

Now, both atoms in KI are larger than the corresponding atoms in LiBr, so LiBr > KI. So the final ordering is:

(highest lattice energy) GaN > MgS > LiBr > KI (lowest lattice energy).