Periodic Trends in Properties — Prelims Strategy

Prelims Strategy

To effectively tackle NEET questions on periodic trends, a systematic approach is essential. \n1. Master the General Trends: First, firmly grasp the general trends for atomic radius, ionic radius, ionization enthalpy, electron gain enthalpy, and electronegativity across periods and down groups.

Visualize these trends on a blank periodic table. \n2. Memorize Key Exceptions: The NEET exam frequently tests exceptions to these general trends. Pay special attention to: \n * Ionization Enthalpy: Group 13 vs.

Group 2 (e.g., Al < Mg), Group 16 vs. Group 15 (e.g., O < N). \n * Electron Gain Enthalpy: F vs. Cl (Cl is more negative than F), positive EGE for noble gases, Group 2, and Group 15 elements. \n * Lanthanide Contraction and its effects on 4d and 5d series elements.

\n3. Isoelectronic Species: For questions involving isoelectronic ions, remember that size is inversely proportional to nuclear charge (Z). The species with the highest Z will be the smallest. \n4.

Nature of Oxides: Understand the transition from basic to amphoteric to acidic oxides across a period. Memorize common amphoteric oxides (Al$_2$O$_3$, ZnO, PbO, SnO$_2$). \n5. Practice Ordering Questions: These are very common.

Practice arranging elements/ions in various orders. When comparing elements from different periods and groups, prioritize the 'down a group' effect (due to new shells) over the 'across a period' effect (due to $Z_{\text{eff}}$) for atomic/ionic size.

\n6. Reasoning Focus: Don't just memorize trends; understand *why* they occur. Relate them to effective nuclear charge, shielding effect, and electron configurations (especially half-filled and fully-filled orbitals).

This helps in solving reasoning-based questions and understanding exceptions.