p-Block Elements - NEET Notes, Formula & Common Mistakes
p-Block Elements·2 min read·NEET 2026
What NEET Asks
Typically 2-3 questions, often tricky, directly from NCERT.
Focus on general trends (atomic size, ionization enthalpy, electronegativity, electron gain enthalpy), anomalous behaviour of first elements, and oxidation states.
Reactions and properties of hydrides, oxides, and halides, especially Group 15, 16, and 17 compounds, are frequently tested.
Key Points
Inert Pair Effect: Stabilises lower oxidation states (e.g., +3 for Group 15, +4 for Group 14, +2 for Group 16) down the group for heavier elements.
Anomalous Behaviour: First element (N, O, F) in each group differs significantly due to small size, high electronegativity, high ionization enthalpy, and absence of d-orbitals.
Hydrides (Group 15-16): Thermal stability decreases down the group. Reducing character increases down the group. Basicity of Group 15 hydrides decreases, while acidic character of Group 16 hydrides increases down the group.
Halogens (Group 17): Reactivity order: F₂ > Cl₂ > Br₂ > I₂. Bond dissociation enthalpy order: Cl₂ > Br₂ > F₂ > I₂ (Fluorine is an exception).
Noble Gases (Group 18): Highly stable due to complete octet. Xenon forms compounds with highly electronegative elements like F₂ and O₂ (e.g., XeF₂, XeF₄, XeF₆, XeO₃, XeOF₄).
2NO(g) + O₂(g) → 2NO₂(g) (Oxidation of nitric oxide)
3NO₂(g) + H₂O(l) → 2HNO₃(aq) + NO(g) (Absorption of nitrogen dioxide in water)
Common Mistakes
Students often confuse the trends for thermal stability, reducing power, and acidic nature of hydrides; remember them distinctly.
Don't forget the anomalous behaviour of fluorine, especially its lower bond dissociation enthalpy compared to chlorine due to lone pair repulsions.
Incorrectly predicting oxidation states or products in complex redox reactions involving p-block elements, particularly for those showing variable valency.
Rapid Revision
Focus on electronegativity, ionization enthalpy, and atomic radius trends. Remember the inert pair effect and anomalous behaviour of N, O, F. Quickly review important industrial processes (Haber, Ostwald, Contact) and the structures/hydrolysis reactions of noble gas compounds.
Frequently Asked Questions
Why does nitrogen show anomalous behaviour compared to other Group 15 elements?▾
Nitrogen exhibits anomalous behaviour due to its small size, high electronegativity, high ionization enthalpy, and the absence of d-orbitals in its valence shell. This allows it to form pπ-pπ multiple bonds and restricts its maximum covalency to four.
Explain the inert pair effect in p-block elements.▾
The inert pair effect refers to the reluctance of the outermost s-electrons to participate in bond formation. This leads to the stability of oxidation states two units lower than the group oxidation state, particularly for heavier elements in Groups 13-16, due to poor shielding by d and f electrons.
How does the acidic character of hydrides change down Group 16 elements?▾
For Group 16 elements (H₂O, H₂S, H₂Se, H₂Te), the acidic character increases down the group. This is because the bond strength (E-H) decreases with increasing atomic size of the central atom (E), making it easier to release a proton.
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