Fajan's Rules (Covalent Character)

$$\text{Covalent Character} \propto \frac{1}{\text{Cation Size}}$$

$$\text{Covalent Character}\propto\text{ Anion Size}$$

$$\text{Covalent Character}\propto\text{ Charge on anion or cation}$$

Concept: Determines the extent of polarization in an ionic bond, where increased distortion of the electron cloud transitions the bond toward higher covalent character.

Notation: Small Cation size increases polarizing power; Large Anion size increases polarizability; High Charge on either ion intensifies polarization; Pseudo-noble gas configuration ($$ns^2 np^6 nd^{10}$$) offers greater polarizing power than a noble gas configuration ($$ns^2 np^6$$).