p-Block and d-Block Elements Class 12: Trends and Important Compounds

Inorganic chemistry is 12–14 marks in boards and the fastest marks in JEE/NEET because it is NCERT-direct. These are the trends and compounds asked most.

p-block trends

• Down a group: metallic character ↑, stability of lower oxidation state ↑ (inert pair effect: Bi³⁺, Pb²⁺, Tl⁺).
• Oxides: N₂O₅, P₄O₁₀ acidic; Bi₂O₃ basic. Group 16: O–O and F–F bonds weak due to lone pair repulsion.
• Halogens: F₂ strongest oxidant; HF weakest acid (H-bonding), HI strongest; Cl₂ + cold NaOH → NaCl + NaOCl; hot → NaClO₃.
• Noble gases: Xe forms XeF₂ (linear, sp³d), XeF₄ (square planar), XeF₆ (distorted octahedral); XeF₆ + H₂O → XeO₃ (pyramidal).

Important p-block compounds

Compound	Preparation / key reaction
NH₃	Haber: N₂ + 3H₂ ⇌ 2NH₃ (Fe, 450°C, 200 atm); Lewis base
HNO₃	Ostwald: NH₃ → NO → NO₂ → HNO₃; Cu + dil. HNO₃ → NO, conc. → NO₂
PCl₅	Trigonal bipyramidal, two longer axial bonds; solid exists as [PCl₄]⁺[PCl₆]⁻
H₂SO₄	Contact process (V₂O₅); oleum H₂S₂O₇; dehydrating, oxidising
O₃	Bent, oxidises PbS to PbSO₄; ozone layer
Interhalogens	XY, XY₃, XY₅, XY₇ (ClF₃ T-shaped, IF₇ pentagonal bipyramidal)

d-block trends

• Variable oxidation states (Mn: +2 to +7), coloured ions (d–d transition; Sc³⁺, Zn²⁺ colourless), paramagnetism, catalysis, alloys, complex formation.
• Cr³⁺ and Mn²⁺ (d⁵) are especially stable; Cu²⁺ is more stable than Cu⁺ in water (hydration enthalpy).
• Lanthanoid contraction: poor shielding by 4f → Zr and Hf nearly identical in size.

KMnO₄ and K₂Cr₂O₇

• KMnO₄: from MnO₂ → K₂MnO₄ → KMnO₄ (electrolytic oxidation). Acidic: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O (n = 5); neutral: → MnO₂ (n = 3); alkaline: → MnO₄²⁻ (n = 1).
• K₂Cr₂O₇: from chromite ore; Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O (n = 6); orange ⇌ yellow (CrO₄²⁻) with pH.

Common mistakes

• Writing XeF₄ as tetrahedral
• Using n = 3 for KMnO₄ in acidic medium
• Saying HF is the strongest halogen acid

Related: Coordination compounds.

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Frequently asked questions

Are these p-Block and d-Block Elements Class 12 notes enough for the exam?

They cover every formula, definition and question type that appears in school and board papers for this chapter. Use them with the NCERT examples, exercise questions and the last five years' papers to be fully prepared.

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Revise the notes after 1 day, 7 days and 30 days. Solve five questions each time instead of only reading, and keep an error list of the steps you get wrong.

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