JEE Main · 2024 · 31 Jan 2024 · Shift 2 · Chemical Bonding and Molecular Structure

By Fajans' rules, covalent character in an ionic compound increases with the polarizing power of the cation and the polarizability of the anion.

$\mathrm{A}{\mathrm{g}}^{+}$ has a pseudo-noble-gas (18-electron), $[\mathrm{Kr}]4d^{10}$ configuration, which gives it much higher polarizing power for its size than ${\mathrm{K}}^{+}$, $\mathrm{B}{\mathrm{a}}^{2+}$, or $\mathrm{C}{\mathrm{o}}^{2+}$. This strongly polarizes the chloride ion in AgCl, pulling electron density toward the covalent limit.

Ionic character order: $\mathrm{KCl}>\mathrm{BaC}{\mathrm{l}}_2>\mathrm{CoC}{\mathrm{l}}_2>\mathrm{AgCl}$; AgCl is the least ionic.