Covalent Character of Ionic Bonds — Prelims Strategy

Prelims Strategy

To effectively tackle NEET questions on the covalent character of ionic bonds, a systematic approach based on Fajans' Rules is essential.

1
Master Fajans' Rules: — Memorize and deeply understand each of the four rules: small cation, large anion, high charge (on either ion), and pseudo-noble gas configuration (for cation). Understand *why* each factor increases polarization.
2
Identify the Variable: — In comparative questions, first identify what is changing (cation, anion, or both) and what is constant.
3
Apply Rules Systematically:

* Cation Size: Smaller cation = more polarizing power = more covalent character. * Anion Size: Larger anion = more polarizable = more covalent character. * Ionic Charge: Higher charge = more polarizing power (cation) or more polarizable (anion) = more covalent character.

* Electronic Configuration: Cations with 18-electron outer shell (e.g., Cu$^+$, Ag$^+$, Zn$^{2+}$) are more polarizing than those with 8-electron noble gas configuration (e.g., Na$^+$, K$^+$) of similar size and charge.

1
Relate to Properties: — Remember the consequences of increased covalent character: lower melting/boiling points, decreased solubility in water (increased in non-polar solvents), and potential for color.
2
Practice Comparative Questions: — Most questions are comparative. Practice arranging compounds in increasing/decreasing order of covalent character or related properties. For example, compare LiCl, NaCl, KCl, RbCl for melting points. Compare AgF, AgCl, AgBr, AgI for color.
3
Beware of Traps: — Common traps include confusing the relationship between covalent character and properties (e.g., thinking more covalent means higher melting point) or overlooking one of Fajans' rules, especially the pseudo-noble gas configuration, which often differentiates transition metal compounds.
4
Conceptual Clarity: — For reasoning-based questions, articulate the role of polarization and specific Fajans' rules clearly.