Partial covalent character of lithium halides

The salts of alkali metals are the most ionic salts known. Although lithium is an alkali metal yet its compounds., particularly halides, are slightly covalent in nature. This is because the Li* ion has small size and has maximum tendency to withdraw the electrons towards itself from the negative ion. In other words, it distorts the electron cloud of the anion towards itself. This distortion of the electron cloud of the negative ion by the positive ionis known as polarization. As a result, the charges on the ions become less because some of its charges get neutralized.

This leads to covalent character. Thus, if polarization is more, larger will be the covalent character of the bond. The polarization depends upon

(i)The polarization increase with decrease in size of the cation.

(ii) The polarization increase with increase in size of the anion because, the anion gets polarized.

If the anion is large, its electron cloud will be weakly held by the nucleus and can be easily deformed towards the cation.

(iii) The polarization increase with increase in charge of the ion (cation or anion).

Thus, Li* being small in size, polarizes the anion and results in decrease of the positive charge on Li* ion. Therefore, lithium halides are covalent in nature. For example, LiI is covalent.