ChemistryMediumClass 11

Trends — Ionization, electronegativity, oxidation states

p-block Elements (Class 11 — Groups 13 & 14)

JEE Qs

Hard

min

Master the exceptions to periodic trends in p-block elements, especially for Groups 13 and 14, focusing on the reasons like inert pair effect and poor shielding by d/f electrons.

🧮 Key Formulas

Z_eff = Z - S (Effective nuclear charge definition, where Z is atomic number and S is shielding constant)

✅ Key Points for JEE

1Ionization energy (IE) generally increases across a period and decreases down a group, but significant exceptions occur in p-block due to poor shielding by d/f electrons and inert pair effect.
2Electronegativity (EN) generally increases across a period and decreases down a group; however, for Groups 13 and 14, the decrease down the group is less regular (e.g., Al has slightly higher EN than Ga due to poor shielding).
3Oxidation states in p-block show the 'inert pair effect' for heavier elements: the lower oxidation state (n-2) becomes more stable than the group oxidation state (n) down the group (e.g., +1 for Group 13, +2 for Group 14).
4The primary reasons for anomalous trends in Groups 13 and 14 are the poor shielding effect of d and f electrons (leading to increased Z_eff) and relativistic effects for very heavy elements, which make the valence s-electrons more tightly bound.
5Specifically, for Group 13, IE: B < Al > Ga < In < Tl. For Group 14, IE: C > Si < Ge < Sn < Pb. These irregularities are crucial.

⚠️ Common Mistakes

✕Assuming monotonic trends for ionization energy and electronegativity down the groups 13 and 14 without considering the effect of d and f orbital contraction/poor shielding.
✕Failing to correctly identify the increasing stability of lower oxidation states (inert pair effect) for heavier elements in Groups 13 (+1) and 14 (+2).
✕Confusing the causes of these exceptions; attributing them solely to size changes without linking to effective nuclear charge and d/f orbital shielding.

NCERT Chapters

Class 11 Chemistry Part 1 Ch 3: Classification of Elements and Periodicity in Properties
Class 11 Chemistry Part 2 Ch 11: The p-Block Elements