Question

Why $\mathrm{LiCl}$ is more covalent than $\mathrm{KCl}$?

Answer 1

Lithium Chloride and Potassium Chloride:

1. Lithium chloride has a chemical formula $\mathrm{LiCl}$.
2. Potassium chloride has a chemical formula $\mathrm{KCl}$.

Covalent Bonding:

1. The anions in $\mathrm{LiCl}$ and $\mathrm{KCl}$ are the same.
2. It can be observed from the periodic table that ${\mathrm{Li}}^{+}$ is smaller than ${\text{K}}^{+}$.
3. The polarising effect of a smaller cation increases along with its covalent nature.
4. As cation size grows, the covalent character reduces. $\mathrm{LiCl}>\mathrm{NaCl}>\mathrm{KCl}>\mathrm{RbCl}>\mathrm{CsCl}$
5. As a result, LiCl has a higher covalent character than $\mathrm{KCl}$, which makes $\mathrm{KCl}$ more soluble in water due to its lower covalent character.
6. As a result, $\mathrm{LiCl}$ has more polarisation than $\mathrm{KCl}$, making it more covalent.

Hence, $\mathrm{LiCl}$ is more covalent than $\mathrm{KCl}$ because of its high polarisation.