Why are lithium compounds covalent in nature?

Lithium compounds tend to exhibit more covalent character than ionic character due to several factors:

Small Size of Lithium Ion (Li
+
+
): The lithium ion is very small with a high charge density. This leads to a high polarizing power, meaning it can distort the electron cloud of the anion it is bonded to. This distortion increases the sharing of electrons between lithium and the anion, leading to covalent character.

High Ionization Energy: Lithium has a relatively high ionization energy compared to other alkali metals. This makes it less favorable for lithium to lose an electron and form a purely ionic bond.

Fajan's Rules: According to Fajan's rules, a small cation with a high charge density and a large anion with a high polarizability will lead to greater covalent character in a bond. Since lithium has a high charge density and tends to form bonds with large anions, the resulting compounds often have significant covalent character.

Comparison with Other Alkali Metals: Compared to other alkali metals like sodium or potassium, lithium compounds are more covalent because lithium's small size makes it more similar to transition metals, which often form covalent bonds.

Examples of lithium compounds that exhibit covalent character include lithium hydride (LiH), lithium chloride (LiCl), and lithium carbonate (Li
2
2
​
CO
3
3
​
). In each case, the polarization effect of the small Li
+
+
ion on the anion leads to a significant sharing of electrons, resulting in covalent bonding.