p-Block

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

p-Block — Quick Facts

The p-block consists of elements in groups 13–18, where the differentiating electron enters a p-orbital. These elements have diverse properties — from metallic (Sn, Pb, Bi) to metalloid (B, Si, Ge, As, Sb, Te) to non-metallic (C, N, O, P, S, halogens, noble gases).

Important Elements and Their Key Properties:

Group 13 (Boron Family — ns² np¹):

• Boron (B): Only metalloid in group 13; forms borax (Na₂B₄O₇·10H₂O); boric acid (H₃BO₃) is a weak monobasic acid; Al(OH)₃ is amphoteric
• Aluminium (Al): Most abundant metal in Earth’s crust; strong reducing agent (E° = −1.66 V); forms Al₂O₃ (alumina, very hard), Al(OH)₃ (gelatinous white precipitate)
• Gallium (Ga): Low melting point (29.8°C); exists as liquid at room temperature

Group 14 (Carbon Family — ns² np²):

• Carbon (C): Forms diamond (hardest natural substance), graphite (layered, used as lubricant and electrode), fullerenes (C₆₀), graphene
• Silicon (Si): Second most abundant element in Earth’s crust; forms SiO₂ (quartz, sand); semiconductor
• Tin (Sn): Allotropes — grey tin (α, < 13.2°C, non-metallic) and white tin (β, metallic); SnO₂ is amphoteric

Group 15 (Nitrogen Family — ns² np³):

• Dinitrogen (N₂): Tripple bond (N≡N), bond enthalpy = 945 kJ/mol — very stable; makes up 78% of atmosphere
• Ammonia (NH₃): Pyramidal geometry, prepared by Haber process (N₂ + 3H₂ ⇌ 2NH₃, Fe catalyst, 400–500°C, 200 atm)
• Nitric acid (HNO₃): Strong acid; oxidising agent; yellow colour due to NO₂ dissolved; prepared by Ostwald process

Group 16 (Oxygen Family — ns² np⁴):

• Ozone (O₃): Triatomic molecule, bent shape; powerful oxidising agent; protects Earth from UV radiation (ozone layer at 25–30 km altitude)
• Sulphur (S): Allotropes — rhombic (α-S, stable at room temperature) and monoclinic (β-S, stable above 95.5°C)

⚡ Exam tip: The inert pair effect (reluctance of s-electrons to participate in bonding) increases down the group — this is why Pb²⁺ is more stable than Pb⁴⁺, and Bi³⁺ more stable than Bi⁵⁺.

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

p-Block — NEET/JEE Study Guide

Allotropes of Phosphorus (NEET Favourite):

Allotrope	Structure	Properties
White phosphorus (P₄)	Tetrahedral molecules; stored under water	Highly reactive, poisonous, glows in dark (chemiluminescence)
Red phosphorus	Polymeric network	Obtained by heating white P at 250°C; less reactive, non-poisonous
Black phosphorus	Layered sheet structure	Most stable allotrope; obtained by heating at high pressure
P₄ (singlet)	Excited state	Very reactive

Group 15 Oxides and Acids:

Oxide	Formula	Nature
N₂O	Laughing gas	Neutral
NO	Nitric oxide	Neutral
N₂O₃	—	Acidic
NO₂	—	Acidic
N₂O₅	—	Acidic

Oxoacids of nitrogen: HNO₂ (nitrous acid, unstable), HNO₃ (nitric acid, stable, strong acid and oxidising agent).

Sulphuric Acid (H₂SO₄) — King of Acids:

• Strong acid: First proton always dissociates (pKₐ₁ = −3, very strong)
• Dehydrating agent: Removes water from sugars (C₁₂H₂₂O₁₁ → 12C + 11H₂O), from CuSO₄·5H₂O (blue → white)
• Oxidising agent: Hot concentrated H₂SO₄ reduces to SO₂
• Contact process for manufacture: 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅ catalyst) → H₂SO₄

Helium and Neon — Noble Gases:

• Helium (He): Second most abundant element in universe; extremely low density; used in balloons and cryogenics (supconducting magnets); non-renewable on Earth
• Neon (Ne): Used in advertising signs (orange-red glow); low density; inert

Hydrogen Peroxide (H₂O₂):

• Strong oxidising agent: H₂O₂ + 2H⁺ + 2e⁻ → 2H₂O (E° = +1.78 V)
• Can also act as reducing agent: H₂O₂ + 2OH⁻ → O₂ + 2H₂O
• Decomposes: 2H₂O₂ → 2H₂O + O₂ (catalysed by light, MnO₂, metal ions)
• Stored in dark bottles (photodecomposition); sometimes stabilised with urea

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

p-Block — Comprehensive Notes

Nitric Acid Manufacturing — Ostwald Process:

1. Ammonia + air → NO + H₂O (Pt/Rh catalyst, 850°C, 9 atm) 4NH₃ + 5O₂ → 4NO + 6H₂O
2. NO + O₂ → NO₂ (cooled, in presence of O₂) 2NO + O₂ → 2NO₂
3. NO₂ + H₂O → HNO₃ + NO 3NO₂ + H₂O → 2HNO₃ + NO (NO recycled)

Interhalogen Compounds (AX, AX₃, AX₅, AX₇):

• More reactive than individual halogens (weaker bond between two different halogens)
• AX type: ClF, BrF, BrCl, ICl, IBr —XX bond is polar
• AX₃ type: ClF₃ (T-shaped), BrF₃ (T-shaped), ICl₃ (T-shaped)
• AX₅ type: ClF₅ (square pyramidal), BrF₅ (square pyramidal)
• AX₇ type: IF₇ (pentagonal bipyramidal)

Pseudohalogens: Species like (CN)₂, (SCN)₂, ICN that behave like halogens. Their anions (CN⁻, SCN⁻) are called pseudohalide ions.

Boron Chemistry (special for NEET):

• Borax (Na₂B₄O₇·10H₂O): Used in qualitative analysis (borax bead test for transition metals); formula can be written as Na₂[B₄O₅(OH)₄]
• Boric acid (H₃BO₃): Weak monobasic acid (not proton donor — accepts OH⁻ from water: B(OH)₃ + H₂O → [B(OH)₄]⁻ + H⁺)
• Diborane (B₂H₆): Electron-deficient compound; bridged structure with two 3-centre-2-electron (3c-2e) bonds

Noble Gas Compounds (Xenon):

• XeF₂ (linear, spontaneously hydrolysis): Xe + F₂ → XeF₂
• XeF₄ (square planar): Xe + 2F₂ → XeF₄ (at 400°C, 5 atm)
• XeF₆ (distorted octahedral): Xe + 3F₂ → XeF₆
• XeO₃ (explosive, trigonal pyramidal)
• Noble gases were once thought to be completely inert — Neil Bartlett synthesised XePtF₆ in 1962, overturning this assumption

Halogen Oxides (NEET importance):

• Cl₂O: Brownish-yellow gas, explosive
• ClO₂: Odd electron molecule (bent), used in water treatment
• Cl₂O₇: anhydride of perchloric acid (HClO₄), explosive
• BrO₃⁻, IO₃⁻: Halates; KBrO₃ used as bread preservative

NEET Pattern Analysis: p-Block contributes 3–4 questions per year. Key areas: anomalous behaviour of first element in each group (B, C, N, O, F), allotropes of phosphorus, nitric acid and sulphuric acid processes, interhalogen compounds, and noble gas chemistry. The inert pair effect and its consequences on stability of +3 vs +5 oxidation states in group 15 is frequently tested.

⚡ NEET 2022 Qn: Which of the following is NOT a property ofionic compounds? (Options including electrical conductivity in aqueous solution — ionic compounds DO conduct electricity when dissolved or molten). A common trap is to say that covalent compounds don’t conduct electricity, but some ionic compounds melt at very high temperatures.