Question

The lattice energy order for lithium halide is:
A. \[LiF>LiCl>LiBr>LiI\]
B. \[LiCl>LiF>LiBr>LiI\]
C. \[LiBr>LiCl>LiF>LiI\]
D. \[LiI>LiBr>LiCl>LiF\]

Answer 1

Hint: Lattice energy depends on the size of the halide ion. As we move from fluorine to iodine among halogens the size of the halogen atom increases and lattice energy decreases.

Complete Step by Step Answer:
Lattice energy depends on the ionic character of the anion of lithium halides. More the ionic character of the lithium halide, the more its lattice energy. Among the lithium halides the lithium metal is highly electropositive as it is an alkali metal.

As we move from lithium fluoride to lithium iodide in lithium halides, the size of the halogen atom that is fluorine to iodine also increases. The polarisation power of the halides increases from fluorine to iodine so, ionic character decreases from lithium fluoride to lithium iodide and lattice energy also decreases. Thus among lithium halides lithium fluoride has the highest and lithium iodide has the lowest lattice energy.

Thus we can write that the order of lattice energy of the lithium halides is as follows:
\[LiF>LiCl>LiBr>LiI\]
Thus the correct option is A.

Additional Information: Iodine is a halogen element. It has the symbol of $I$. It generally exists as a gas. It has the colour of violet blue. Iodine is generally obtained from seaweed. Starch generally acts as an indicator in titration reactions to determine the end point of a titration. Iodine gas reacts with starch, an indicator gives blue colour.

Note: Lattice energy can be defined as the energy that must be required to separate one mole of an ionic crystal into gaseous ions in a vacuum through an endothermic process. It depends on the ionic character of a compound.