Question

KCl has higher melting point than AgCl. Why?

[$r_{A{g}^{+}}$ $\approx$ $r_{K^{+}}$]

• A. Cation size
• B. Anion size
• C. Pseudo noble gas cation
• D. Cation charge

Answer 1

The correct option is C

Pseudo noble gas cation

Its given that cation sizes are nearly same, The cations are $K^{+}$ and ${Ag}^{+}$.

$K^{+}$= [Ar] while ${Ag}^{+}$ = [Kr]4$d^{10}$

By looking at the $e^{-}$ configurations, $K^{+}$ has noble gas configuration and ${Ag}^{+}$ has pseudo noble gas configuration beacuse of filled d-orbitals.

Such pseudo-noble gas configurations leads to more polarizing power beacuse of ineffective shielding of d-electrons.Thus ${Cl}^{-}$ is more polarized in case of AgCl.

Thus,Agcl is more covalent than KCI and hence has lesser melting point