Concept Explanation: Polarization in Ionic Compounds

Polarization refers to the distortion of the electron cloud of an anion by the cation in an ionic compound. Higher polarization occurs when the cation has a high charge density, which depends on its charge and size.

Step 1: Understand the Cations Involved

AgCl contains Ag⁺ ion, and KCl contains K⁺ ion.

Step 2: Compare Cation Sizes

Size of Ag⁺ ion is smaller (approx. 129 pm) compared to K⁺ ion (approx. 152 pm). Smaller size means higher charge density.

Charge density formula: $\mathrm{Charge\; Density}=\frac{\mathrm{Charge}}{\mathrm{Size}}$

Step 3: Compare Electronic Configurations

K⁺ has inert gas configuration [Ar]. Ag⁺ has pseudo inert gas configuration [Kr] 4d¹⁰. The d¹⁰ configuration in Ag⁺ makes it more polarizable and better at polarizing anions.

Step 4: Determine the Key Factor

While both smaller size and pseudo inert gas configuration contribute, the pseudo inert gas configuration of Ag⁺ is the primary reason for higher polarization in AgCl compared to KCl.

Final Answer

Higher polarization in case of AgCl compared to KCl is due to pseudo inert gas configuration of cation.

Related Topics

• Fajans' Rules
• Ionic and Covalent Character
• Polarizing Power and Polarizability
• Lattice Energy

Important Formulae and Theory

Fajans' Rules: Predict covalent character in ionic compounds:

1. Small cation size → More polarization
2. Large anion size → More polarization
3. High charge on ions → More polarization

Polarizing Power: $P\propto \frac{\mathrm{Charge}}{{\mathrm{Size}}^2}$

Pseudo Inert Gas Configuration: Cations with 18 electrons in outermost shell (ns²np⁶nd¹⁰) have higher polarizing power than those with 8 electrons.