The p-Block Elements — NEET Revision

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The Cheat Sheet Dashboard

Scan these golden rules first — they answer most multiple-choice traps.

Group 13 — Boron Family

B, Al, Ga, In, Tl · outer config ns² np¹ · common oxidation state +3.

Heavier elements (In, Tl) prefer the +1 state — inert pair effect. B is a non-metal (covalent); the rest are metals.

+3 commonTl⁺ stable

Group 14 — Carbon Family

C, Si, Ge, Sn, Pb · outer config ns² np² · common oxidation state +4; heavier prefer +2.

Catenation order: C ≫ Si > Ge ≈ Sn ≫ Pb. C–C bonds form long chains; Pb²⁺ dominant due to inert pair.

+4 commonPb²⁺ stableC catenates

Anomalous Behaviour (B & C)

The first member of each group stands apart — small size, high IE/EN, and no d-orbitals.

So B can't expand octet (max BF₄⁻, no BF₆³⁻); C forms strong p–p multiple bonds (CO₂, alkenes/alkynes) — Si prefers single bonds and gives 3-D SiO₂.

No d-orbitalsp–p π bonds in C

Inert Pair Effect

Down a group, the outer ns² electrons increasingly stay put (poor shielding by d/f electrons → high penetration).

⇒ Heavier elements show a stable oxidation state 2 less than the group state: Tl⁺ and Pb²⁺ are the most stable. Pb⁴⁺ is a strong oxidiser; Sn²⁺ is a strong reducer.

PbCl₂ stablePbCl₄ unstable

Diagonal Relationship

Li↔Mg, Be↔Al, B↔Si — similar size & polarising power across a diagonal.

So B (Group 13) and Si (Group 14) both form covalent polymeric oxides, weak acidic oxides, and stable hydrides — not behaviour you'd expect from groupmates alone.

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Interactive Periodic Trends

Easy Explanation

Pick a property and a group, then watch how it changes as you walk down the column. You'll see clean trends — and the funny "kinks" examiners love to test (e.g. Al < B in IE, but Ga > Al because of poor d-shielding).

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Inert-Pair Effect Explorer

Easy Explanation

Pick an element from Group 13 or 14 — the explorer tells you its most stable oxidation state, why, and the practical NEET consequence (Pb⁴⁺ oxidises, Sn²⁺ reduces, etc.).

Choose an element:

Most stable state+3

Group 13 — non-metal

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Mentor's Tip — Inert Pair Rule

🎯 Pick the right oxidation state — fastHigh priority

Before guessing the oxidation state of a heavy p-block element, ask: "Am I above or below the diagonal?" Light elements stick to the group state; heavy elements drop by 2 thanks to the inert pair effect.

Group 13 default: +3 for B, Al, Ga — but +1 for Tl (Tl³⁺ is a strong oxidiser, TlCl₃ < TlCl in stability).
Group 14 default: +4 for C, Si, Ge — but +2 for Pb. Sn shows both (Sn²⁺ is a reducer, Sn⁴⁺ stable).
The trap: Pb⁴⁺ compounds (PbO₂, PbCl₄) are oxidising agents; Sn²⁺ compounds (SnCl₂) are reducing agents. Memorise this pair!
Why? Going down, the ns² pair is held tighter (poor d/f shielding), so it doesn't take part in bonding.

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Quick Reactions & Key Compounds

Easy Explanation

The handful of reactions and structures that account for most NEET questions on this chapter. Memorise the right-hand side.

Boron trifluoride — Lewis acidBF₃ + NH₃ → F₃B←NH₃ (Lewis adduct)

Boric acid — Lewis acid in waterB(OH)₃ + H₂O → [B(OH)₄]⁻ + H⁺

Diborane preparation4BF₃ + 3LiAlH₄ → 2B₂H₆ + 3LiAlF₄

Diborane → borazine3B₂H₆ + 6NH₃ → 2B₃N₃H₆ + 12H₂ ("inorganic benzene")

Diborane combustionB₂H₆ + 3O₂ → B₂O₃ + 3H₂O (highly exothermic, ΔH = −2025 kJ)

Amphoteric Al₂O₃Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O · Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

AlCl₃ — exists as a dimer2AlCl₃ ⇌ Al₂Cl₆ (banana/Lewis-adduct bridges)

Silica hydrolysisSiCl₄ + 4H₂O → Si(OH)₄ → SiO₂ + 2H₂O

Silicone polymern Me₂SiCl₂ + n H₂O → (Me₂SiO)_n + 2n HCl · Me₃SiCl caps the chain.

CO from formic acidHCOOH ⟶(conc. H₂SO₄) CO + H₂O

CO₂ from CaCO₃CaCO₃ ⟶(heat) CaO + CO₂↑

Pb²⁺ vs Sn²⁺Sn²⁺ → Sn⁴⁺ + 2e⁻ (reducer) · Pb⁴⁺ + 2e⁻ → Pb²⁺ (oxidiser)

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Must-Memorise — for Aamirah

📌 Lock these into memory before exam day, Aamirah. These are the orders, formulas, hybridisations and odd-one-outs that NEET examiners love. Glance over this section every revision day and you’ll never trip on a one-mark question. ❤️

1Group Configurations & Character

Group 13 (B, Al, Ga, In, Tl): ns² np¹ · common +3 · B is non-metal, rest metals; Tl⁺ most stable.
Group 14 (C, Si, Ge, Sn, Pb): ns² np² · common +4 · C non-metal, Si/Ge metalloids, Sn/Pb metals; Pb²⁺ most stable.
Metallic character increases down both groups.

2Trend Orders (memorise verbatim)

1st IE — Group 13: B > Tl > Ga > Al > In (not monotonic!)
Atomic radius — Group 13: Tl > In > Al > Ga > B (Ga < Al kink)
Atomic radius — Group 14: Pb > Sn > Ge > Si > C
1st IE — Group 14: C > Si > Ge > Pb > Sn (Pb > Sn due to f-shielding)
Electronegativity (Group 14): C ≫ Si ≈ Ge ≈ Sn < Pb (C highest by far)

3Acidity Orders

Lewis acidity of BX₃: BF₃ < BCl₃ < BBr₃ < BI₃ (back-bonding from F weakens BF₃).
Group 13 oxides: B₂O₃ acidic → Al₂O₃, Ga₂O₃ amphoteric → In₂O₃, Tl₂O₃ basic.
Group 14 oxides: CO₂, SiO₂ acidic · GeO₂ weakly acidic · SnO, PbO amphoteric · SnO₂, PbO₂ amphoteric.
Boric acid H₃BO₃ is a monobasic Lewis acid (accepts OH⁻, doesn’t donate H⁺).

4Catenation & Bond Strengths

Catenation: C ≫ Si > Ge ≈ Sn ≫ Pb.

C–C≈ 348 kJ/mol

Si–Si≈ 226

Ge–Ge≈ 188

Sn–Sn≈ 151

C=O≈ 805 (strong p–π)

Si=Oweak (no good p–π)

5Hybridisation Cheat-Sheet

BF₃ / BCl₃ / B in B(OH)₃sp²

BF₄⁻ / [B(OH)₄]⁻ / B in B₂H₆sp³

Al in Al₂Cl₆sp³

C in CO₂sp (linear)

C in CO₃²⁻ / graphitesp²

C in CH₄ / CCl₄ / diamondsp³

Si in SiF₆²⁻sp³d² (octahedral)

Borazine ring (B & N)sp²

6Key Compounds & Their Formulas

BoraxNa₂B₄O₇·10H₂O

Boric acidH₃BO₃ or B(OH)₃

DiboraneB₂H₆

Borazine (inorganic benzene)B₃N₃H₆

CarborundumSiC

Quartzcrystalline SiO₂

Producer gasCO + N₂

Water gasCO + H₂

Red leadPb₃O₄

White lead2PbCO₃·Pb(OH)₂

7Inert-Pair Trio (oxidiser vs reducer)

Oxidising agents: Tl³⁺, Pb⁴⁺ (PbO₂, PbCl₄, Pb₃O₄) — they want to drop back to Tl⁺ / Pb²⁺.
Reducing agents: Sn²⁺ (SnCl₂), Ga⁺ — they want to climb to Sn⁴⁺ / Ga³⁺.
Most stable +1 in Group 13 → Tl⁺. Most stable +2 in Group 14 → Pb²⁺.
Order of inert-pair effect: C < Si < Ge < Sn < Pb.
Thermal stability: PbCl₂ > PbBr₂ > PbI₂; PbCl₂ > PbCl₄.

8Anomalies & “Doesn’t Exist”

BF₆³⁻ does NOT exist — B has no d-orbitals (max coord. = 4).
SiF₆²⁻ exists; CF₆²⁻ does NOT (Si has 3d-orbitals).
CO₂ is a gas; SiO₂ is a 3-D solid (no p–π in Si).
B³⁺ cation does NOT exist — B forms covalent bonds (high IE, small size).
Only C in Group 14 forms p–p multiple bonds readily (C=C, C≡C, C=O).
Anhydrous AlCl₃ exists as Al₂Cl₆ dimer (in water, as [Al(H₂O)₆]³⁺).
HF attacks glass: SiO₂ + 4HF → SiF₄ + 2H₂O.
Boric acid is monobasic and Lewis, not Brønsted.

9Numbers Worth Memorising

Ga: mp / bp30°C / ~2400°C

B: mp~2453 K (very high)

Diamond C–C–C angle109.5° (sp³)

Graphite C–C–C angle120° (sp²)

Fullerene C₆₀ rings12 pentagons + 20 hexagons

ΔH (B₂H₆ combustion)≈ −2025 kJ/mol

C–H bond energy≈ 414 kJ/mol

CO bond order3 (triple bond)

Pauling EN — C2.5 (highest in Gr 14)

10Reactions to Recall in One Line

BF₃ + 3H₂O → H₃BO₃ + 3HF (hydrolysis)
B₂H₆ + 6H₂O → 2H₃BO₃ + 6H₂
3B₂H₆ + 6NH₃ → 2B₃N₃H₆ + 12H₂ (borazine)
Al + NaOH + H₂O → NaAlO₂ + H₂↑ (amphoteric Al)
2Al + 6HCl → 2AlCl₃ + 3H₂↑
SiO₂ + 4HF → SiF₄ + 2H₂O
Si + 2NaOH + H₂O → Na₂SiO₃ + 2H₂
n Me₂SiCl₂ + n H₂O → (Me₂SiO)_n + 2n HCl (silicone)
SnCl₂ + 2HgCl₂ → SnCl₄ + Hg₂Cl₂ (Sn²⁺ reducer)

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Quick-Recall Flashcards

Tap a card to flip and reveal the high-yield fact.

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Easy Explanation — Line by Line

Each key idea of the chapter in plain words, with 5 possible NEET questions for each. Tap "Show answer" on any one.

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Exceptions to Remember

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Examples & Reference Data

Element / Compound	Significance / Use

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Solved Problems — Explained & Worked

Representative numericals/conceptuals on each topic, with an easy explanation and a step-by-step answer.

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50 NEET / AIPMT-Pattern PYQs — Solved

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25 JEE-Pattern PYQs — Solved

🎯 p-Block Revision Pack — Groups 15, 16, 17, 18

📅 Built: 2026-07-20 Target: Top-score Inorganic

Dense, exam-only revision for the four p-Block groups you must know cold. 🔥 flags the highest-yield facts NEET repeats every year. Strict-NCERT throughout; any beyond-NCERT item is rose-tagged. All equations balanced; all bond angles, hybridisations and oxidation states exact.

1 Periodic Trends Down the Group Always tested

Property	Group 15 (N→Bi)	Group 16 (O→Po)	Group 17 (F→At)	Group 18 (He→Rn)
Atomic / ionic radius	Increases	Increases	Increases	Increases
Ionisation enthalpy	Decreases	Decreases	Decreases	Decreases (still very high)
Electronegativity	Decreases	Decreases	Decreases	Not usually assigned
Metallic character	Increases (N,P non-metal → As,Sb metalloid → Bi metal)	Increases (O,S non-metal → Se,Te metalloid → Po metal)	All non-metals; slight metallic in I / At	All non-metals
Melting / boiling point	MP: rises to As, falls to Bi; BP: increases	Increases (O₂ gas → Po solid)	Increases (F₂,Cl₂ gas → Br₂ liquid → I₂ solid)	Increases (all monatomic gases)
Electron gain enthalpy	Less negative overall (unlike Gr 16/17)	O less negative than S (small size, e⁻–e⁻ repulsion)	Cl more negative than F ⚠️ (F small size)	Positive (do not accept e⁻)

Key irregularities NEET loves

🔥Cl has more negative ΔH_eg than F — small size of F ⇒ electron–electron repulsion in the compact 2p subshell.
🔥O has less negative ΔH_eg than S — same reason (small O atom).
🔥Group 15 IE₁ order: N > P > As > Sb < Bi — Bi break due to poor shielding; extra-stable half-filled 2p³ raises N.
Group 15 melting point: N < P < As > Sb > Bi (peak at As).
Bond dissociation enthalpy of X₂: Cl₂ > Br₂ > F₂ > I₂ — F₂ low due to small size / lone-pair repulsion.

2 Oxidation States & Inert-Pair Effect

Group	Common OS	Trend / notes
15	−3, +3, +5	+5 stability decreases down (Bi⁺³ stable, Bi⁺⁵ strong oxidiser) — inert pair effect on 6s²
16	−2, +2, +4, +6	+6 stability decreases down; Po prefers +2/+4; O only ±2 (no d-orbitals)
17	−1, +1, +3, +5, +7	F: only −1 (no d-orbitals, most EN); others show +1 to +7 (odd values, use d-orbitals)
18	0 (mostly); Xe: +2, +4, +6, +8	Only Xe and Kr form compounds. XeO₄ has +8. Rn is radioactive.

🔥Inert pair effect: reluctance of ns² pair to bond ⇒ lower OS more stable down the group. Seen in Bi, Pb, Tl.
PbCl₄ decomposes to PbCl₂ + Cl₂ on heating; PbCl₂ is stable. Similarly BiCl₅ doesn't exist as isolable.
NCl₃ exists but NF₅ / NCl₅ do NOT (N has no d-orbitals). PCl₅ exists (P uses 3d).
F never shows positive OS. Cl → +7 in HClO₄; I → +7 in IF₇ / HIO₄.

3 Anomalous Behaviour of the First Element One-mark magnet

First element	Why it's anomalous	Specific NCERT anomalies
N (Group 15)	Small size · high EN · no d-orbitals · pπ–pπ multiple bonding	Only element to form pπ–pπ triple bond (N≡N gas, others solid); no pentahalide (NCl₅ etc. absent); NH₃ is basic, others less basic; N does not catenate significantly
O (Group 16)	Small size · high EN · no d-orbitals · strong pπ–pπ bonds	O₂ is a gas (S₈ solid); H₂O liquid (H-bonding) vs H₂S gas; only −2 and −1 (in peroxide) as OS; no expanded octet (no OF₆)
F (Group 17)	Smallest · most EN · no d-orbitals · low bond dissociation	Only OS = −1; HF is liquid (H-bonded); F₂ has anomalously low bond enthalpy; no oxoacids of the +7 type; forms strong H-bonds
He (Group 18)	1s² fully filled · smallest · very light	Does not form any known compound; used in cryogenics (bp 4.2 K); does not solidify at atm pressure

4 One-liner Facts & Exceptions MCQ-ready

🔥Group 15 hydrides thermal stability: NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃ (BiH₃ least stable — bond energy falls down).
🔥Group 15 hydrides basic strength: NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃ (matches lone-pair availability).
Group 15 hydrides bond angle: NH₃ 107.8° > PH₃ 93.6° > AsH₃ 91.8° > SbH₃ 91.3° > BiH₃ 90°.
Group 15 hydrides reducing character: BiH₃ > SbH₃ > AsH₃ > PH₃ > NH₃ (reverse of stability).
🔥Group 16 hydrides acidic order: H₂O < H₂S < H₂Se < H₂Te < H₂Po (bigger, weaker H–X bond ⇒ easier release of H⁺).
Group 16 hydrides thermal stability: H₂O > H₂S > H₂Se > H₂Te.
Group 16 hydrides reducing character: H₂O < H₂S < H₂Se < H₂Te.
Group 16 hydrides bond angle: H₂O 104.5° > H₂S 92° > H₂Se 91° > H₂Te 90°.
🔥Halogens oxidising power: F₂ > Cl₂ > Br₂ > I₂. Reducing character of X⁻: I⁻ > Br⁻ > Cl⁻ > F⁻.
HX acidic strength: HF < HCl < HBr < HI (bond enthalpy dominates, not EN).
HX bond enthalpy: HF > HCl > HBr > HI. HF liquid only one due to H-bonding.
🔥Halogen oxoacid acidity (same halogen): HXO < HXO₂ < HXO₃ < HXO₄ (higher OS ⇒ stronger acid).
Halogen oxoacid acidity (same OS +1): HOCl > HOBr > HOI.
ClF₃, BrF₃, IF₅, IF₇ are the main interhalogens tested. IF₇ has pentagonal bipyramidal geometry, sp³d³.
Noble gas compounds: only Xe and (limited) Kr. Xenon fluorides XeF₂, XeF₄, XeF₆.
Noble gas He boils at 4.2 K (lowest of all elements); Xe used in high-intensity photographic flashes.
N₂ triple bond dissociation enthalpy ≈ 941 kJ mol⁻¹ (highest for diatomic non-metal).
White P (P₄, tetrahedral, angle 60°) is more reactive than red P (polymeric, less reactive).
🔥Ammonia industrial: Haber process, 200 atm, 700 K, Fe catalyst + Mo promoter.
🔥HNO₃ industrial: Ostwald process — NH₃ → NO → NO₂ → HNO₃. Pt/Rh catalyst at 500 K.
H₂SO₄ industrial: Contact process. Key step: 2SO₂ + O₂ ⇌ 2SO₃ over V₂O₅ at 720 K.
Bleaching action of Cl₂: oxidation (permanent); of SO₂: reduction (temporary).
Ozone O₃ bond angle: 117°. Structure: bent, with resonance. sp² central O.
Ozone estimated by iodometry: 2 KI + O₃ + H₂O → 2 KOH + I₂ + O₂.
P₄O₁₀ + H₂O → H₃PO₄ (drying agent for gases except NH₃).
All group 18 elements are monatomic and colourless; Kr, Xe, Rn discovered after Ar. Ar is most abundant noble gas in air (~0.93 %).

5 Preparation & Key Reactions (balanced)

Group 15 — Ammonia (NH₃)

Haber: N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g) · 200 atm · 700 K · Fe/Mo

Lab: 2 NH₄Cl + Ca(OH)₂ → CaCl₂ + 2 NH₃ + 2 H₂O

Basic: NH₃ + HCl → NH₄Cl (white fumes — test)

With CuSO₄: 4 NH₃ + Cu²⁺ → [Cu(NH₃)₄]²⁺ (deep blue)

Group 15 — Nitric Acid (HNO₃)

Ostwald step 1: 4 NH₃ + 5 O₂ →(Pt/Rh, 500 K) 4 NO + 6 H₂O

Ostwald step 2: 2 NO + O₂ → 2 NO₂

Ostwald step 3: 3 NO₂ + H₂O → 2 HNO₃ + NO

Brown ring test: [Fe(H₂O)₅NO]²⁺ (brown ring at H₂SO₄ interface for NO₃⁻)

Group 15 — Phosphorus compounds

PCl₃ hydrolysis: PCl₃ + 3 H₂O → H₃PO₃ + 3 HCl

PCl₅ hydrolysis: PCl₅ + 4 H₂O → H₃PO₄ + 5 HCl

PCl₅ thermal: PCl₅ ⇌ PCl₃ + Cl₂ (dissociates on heating)

Group 16 — Sulphur compounds

Contact: S + O₂ → SO₂ ; 2 SO₂ + O₂ ⇌(V₂O₅, 720 K) 2 SO₃

Oleum: SO₃ + H₂SO₄ → H₂S₂O₇ ; H₂S₂O₇ + H₂O → 2 H₂SO₄

SO₂ + Cl₂ + activated C: SO₂ + Cl₂ → SO₂Cl₂ (sulphuryl chloride)

Group 16 — Ozone (O₃)

Silent electric discharge: 3 O₂ ⇌ 2 O₃ (endothermic; ΔH = +142 kJ/mol)

Estimation: 2 KI + O₃ + H₂O → 2 KOH + I₂ + O₂

Group 17 — Chlorine (Cl₂)

Deacon: 4 HCl + O₂ →(CuCl₂, 723 K) 2 Cl₂ + 2 H₂O

Lab (MnO₂): MnO₂ + 4 HCl → MnCl₂ + Cl₂ + 2 H₂O

With NaOH (cold, dilute): Cl₂ + 2 NaOH → NaCl + NaOCl + H₂O

With NaOH (hot, conc): 3 Cl₂ + 6 NaOH → 5 NaCl + NaClO₃ + 3 H₂O

Bleaching powder: 2 Ca(OH)₂ + 2 Cl₂ → Ca(OCl)₂ + CaCl₂ + 2 H₂O

Group 17 — HCl (lab)

Lab prep: NaCl + H₂SO₄(conc, 420 K) → NaHSO₄ + HCl

Group 18 — Xenon fluorides

XeF₂: Xe + F₂ →(400 °C, 1 atm, 1:5) XeF₂

XeF₄: Xe + 2 F₂ →(400 °C, 6 atm, 1:5) XeF₄

XeF₆: Xe + 3 F₂ →(300 °C, 60–70 atm, 1:20) XeF₆

Hydrolysis: XeF₆ + 3 H₂O → XeO₃ + 6 HF (also 2 XeF₆ + SiO₂ → 2 XeOF₄ + SiF₄)

6 Structures, Hybridisation & Shape

Compound	Central atom	Hyb.	Shape	Bond angle	LP on central
NH₃	N	sp³	Trigonal pyramidal	107.8°	1
PCl₅ (gas)	P	sp³d	Trigonal bipyramidal	90° / 120°	0
PCl₅ (solid)	—	—	[PCl₄]⁺ (sp³, td) + [PCl₆]⁻ (sp³d², oct)	109.5° / 90°	0 / 0
P₄	P	sp³	Tetrahedral cluster	60° (P–P–P)	1 each
P₄O₆	P	sp³	Cage: 4 P at corners, 6 O bridges	—	1 each P
P₄O₁₀	P	sp³	Like P₄O₆ + 4 terminal P=O	—	0 (all bonded)
SO₂	S	sp²	Bent	119.5°	1
SO₃	S	sp²	Trigonal planar	120°	0
H₂SO₄	S	sp³	Tetrahedral	109.5°	0
SF₆	S	sp³d²	Octahedral	90°	0
SF₄	S	sp³d	See-saw (distorted TBP)	—	1 (equatorial)
O₃	O	sp²	Bent (V-shape)	117°	1
ClF₃	Cl	sp³d	T-shape	87.5°	2
BrF₅	Br	sp³d²	Square pyramidal	90°	1
IF₇	I	sp³d³	Pentagonal bipyramidal	72° / 90°	0
XeF₂	Xe	sp³d	Linear	180°	3
XeF₄	Xe	sp³d²	Square planar	90°	2
XeF₆	Xe	sp³d³	Distorted octahedral	—	1
XeOF₄	Xe	sp³d²	Square pyramidal	—	1
XeO₃	Xe	sp³	Trigonal pyramidal	—	1
XeO₄	Xe	sp³	Tetrahedral	109.5°	0

7 Oxoacids

Group 15 oxoacids of P

Name	Formula	OS of P	Basicity	P–H bonds	Notes
Hypophosphorous	H₃PO₂ (H₂PO₂ + 1 P–H)	+1	Monobasic	2	Strong reducing
Phosphorous	H₃PO₃	+3	Dibasic	1	Reducing (has P–H)
Metaphosphoric	(HPO₃)ₙ	+5	Polymeric	0	—
Pyrophosphoric	H₄P₂O₇	+5	Tetrabasic	0	—
Orthophosphoric	H₃PO₄	+5	Tribasic	0	Most stable P oxoacid

Rule: Basicity = number of O–H (not P–H). Reducing property needs at least one P–H bond.

Group 16 oxoacids of S

Name	Formula	OS of S	Basicity
Sulphurous	H₂SO₃	+4	Dibasic
Sulphuric	H₂SO₄	+6	Dibasic (strong)
Pyrosulphuric (oleum)	H₂S₂O₇	+6	Dibasic
Thiosulphuric	H₂S₂O₃	+2 (avg)	Dibasic
Peroxymonosulphuric (Caro's)	H₂SO₅	+6	Dibasic (peroxo)
Peroxydisulphuric (Marshall's)	H₂S₂O₈	+6	Dibasic (peroxo)

Group 17 oxoacids of Cl

Name	Formula	OS of Cl	Basicity
Hypochlorous	HOCl	+1	Monobasic
Chlorous	HClO₂	+3	Monobasic
Chloric	HClO₃	+5	Monobasic
Perchloric	HClO₄	+7	Monobasic (strongest halogen oxoacid)

Acidic strength: HClO₄ > HClO₃ > HClO₂ > HOCl (more O ⇒ better delocalisation of –ve charge on conjugate base).

8 Hydrides · Oxides · Halides — Comparison

Group 15 hydrides EH₃

Property	Order
Thermal stability	NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃
Basicity	NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃
Reducing power	BiH₃ > SbH₃ > AsH₃ > PH₃ > NH₃
Boiling point	NH₃ > SbH₃ > AsH₃ > PH₃ (irreg. — H-bonding in NH₃)
Bond angle (E–H–E)	107.8° · 93.6° · 91.8° · 91.3° · 90°

Group 16 hydrides H₂E

Property	Order
Thermal stability	H₂O > H₂S > H₂Se > H₂Te > H₂Po
Acidic strength	H₂O < H₂S < H₂Se < H₂Te (opposite of stability)
Reducing power	H₂O < H₂S < H₂Se < H₂Te
Bond angle	104.5° · 92° · 91° · 90°
Boiling point	H₂O > H₂Te > H₂Se > H₂S (H₂O anomaly = H-bond)

Group 17 halides / hydrides HX

Property	Order
Bond dissociation enthalpy (HX)	HF > HCl > HBr > HI
Acidic strength (aq.)	HF < HCl < HBr < HI
Boiling point	HF > HI > HBr > HCl (HF H-bonded)
Reducing power	HF < HCl < HBr < HI
Oxidising power of X₂	F₂ > Cl₂ > Br₂ > I₂
Bond enthalpy (X₂)	Cl₂ > Br₂ > F₂ > I₂ (F₂ anomaly)

9 Colours · Smells · Physical Cues One-mark magnets

NO — colourless; NO₂ — brown; N₂O₃ — blue liquid; N₂O₄ — colourless.
Cl₂ — greenish-yellow; Br₂ — reddish-brown liquid; I₂ — violet solid, violet vapour.
F₂ — pale yellow gas; ClF₃ — colourless gas; ICl — red-brown solid; ICl₃ — orange solid.
SO₂ — colourless, pungent, suffocating smell; H₂S — rotten-egg smell; SO₃ — colourless.
O₃ — pale blue gas, characteristic pungent (chlorine-like) smell.
NH₃ — colourless, characteristic sharp smell; HCl gas — colourless, pungent, white fumes with NH₃.
P₄ (white) — waxy, translucent, garlic-like smell, glows in dark (chemiluminescence).
Red P — dark red / violet, non-poisonous, no glow.
Xenon fluorides all colourless solids. XeO₃ colourless explosive solid.
Rn — colourless, radioactive; He, Ne, Ar, Kr, Xe all colourless.
Bleaching powder — pale yellow, chlorine-like smell.
Aqua regia (3 HCl : 1 HNO₃) — orange fumes, dissolves Au and Pt.

10 Numbers & Values

Item	Value
N≡N bond enthalpy	≈ 941 kJ mol⁻¹
Ammonia synthesis (Haber)	200 atm · 700 K · Fe catalyst · Mo promoter
Contact process temp	720 K over V₂O₅
Ostwald catalyst temp	500 K over Pt/Rh gauze
Ozone formation ΔH	+142 kJ mol⁻¹ (endothermic)
NH₃ bond angle	107.8°
H₂O bond angle	104.5°
O₃ bond angle	117°
SO₂ bond angle	119.5°
P₄ bond angle (P–P–P)	60°
He boiling point	4.2 K (lowest of all elements)
Ar abundance in dry air	≈ 0.93 %
XeF₆ synthesis	Xe : F₂ = 1 : 20, 300 °C, 60–70 atm
HClO₄ Kₐ	Very large (strongest halogen oxoacid)
Halogens diatomic bond enthalpy order	Cl₂ 242 > Br₂ 192 > F₂ 158 > I₂ 151 (kJ/mol)

11 Trap Pairs / Easily Confused

H₃PO₃ dibasic vs H₃PO₄ tribasic — basicity counts O–H, not H (P–H doesn't ionise).

PCl₃ vs PCl₅ hydrolysis — H₃PO₃ vs H₃PO₄. Water molecules needed: 3 vs 4.

SO₂ bleaching (temporary, reduction) vs Cl₂ bleaching (permanent, oxidation).

F₂ oxidises most but HF is weakest acid — bond enthalpy dominates HX acidity.

ΔH_eg: Cl > F, S > O (not the other way!) — small-atom repulsion.

PCl₅ gas (TBP) vs PCl₅ solid ([PCl₄]⁺[PCl₆]⁻) — different structures.

XeF₂ sp³d linear (3 LP) vs XeF₄ sp³d² square-planar (2 LP).

NCl₃ (exists) vs NF₅ / NCl₅ (do NOT exist) — no d-orbital in N.

H₂O highest bp in Gr 16 hydrides, but lowest acidity — H-bonding effect vs bond strength.

Bond enthalpy of X₂: Cl > Br > F > I. F₂ is the anomaly (not smallest ⇒ strongest).

Brown ring test (nitrate) vs Ring test with H₂SO₄ interface. Complex is [Fe(H₂O)₅NO]²⁺.

White P (P₄) reactive, poisonous vs Red P polymeric, non-poisonous.

N₂O laughing gas vs NO colourless vs NO₂ brown.

H₂SO₄ dehydrating agent (removes H₂O from sugar → C).

HClO₄ strongest, HOCl weakest oxoacid of Cl — more O ⇒ more acidic.

12 Mnemonics

Group 15 elements — "Nothing Plus Ask Sb Billy" → N, P, As, Sb, Bi.

Group 16 (chalcogens) — "Our School Selects Tens Points" → O, S, Se, Te, Po.

Group 17 (halogens) — "Fast Clever Brown Indian Athlete" → F, Cl, Br, I, At.

Group 18 (noble) — "Help Needed At Krishna's Xerography Rn" → He, Ne, Ar, Kr, Xe, Rn.

Bond angle of Group 15 hydrides — "NH₃ = 107.8, drops to nearly 90 by BiH₃". Just N is odd; rest ≈ 90°.

Reducing power of Gr 15 hydrides = reverse of stability. Say: "BiH₃ boasts, NH₃ humbles."

Halogen oxoacid acidic order — "HO-Cl less to more O = more acidic". HOCl < HClO₂ < HClO₃ < HClO₄.

Colour of Cl₂, Br₂, I₂ — "Green Yellow, Red Brown, Violet" — like traffic lights going darker.

Xe fluoride LP count — XeF₂ = 3, XeF₄ = 2, XeF₆ = 1. "3, 2, 1 count-down."

Contact process: "V₂O₅ vanquishes oxygen at 720 K". Haber: "Fe/Mo" at "200 atm / 700 K".

13 Cross-Topic Connections

Chemical Bonding → hybridisation (sp³, sp³d, sp³d², sp³d³), VSEPR, back-bonding (BF₃, SO₂).
Redox → oxidising/reducing behaviour of halogens, ozone, HNO₃, H₂SO₄. Balancing in acidic / basic media.
Equilibrium → contact process, Haber process — Le Chatelier arguments for T and P.
s-Block → contrast basicity of NH₃ with alkali hydroxides; peroxide/superoxide of Na, K vs H₂O₂.
d-Block → V₂O₅ (contact), Pt/Rh (Ostwald), Fe (Haber) — catalyst identity is scored.
Coordination compounds → [Cu(NH₃)₄]²⁺ blue, [Fe(H₂O)₅NO]²⁺ brown ring (both use NH₃ / NO from Gr 15).
Environmental chem → SO₂/NO₂ acid rain, ozone hole (CFC → ClO• radicals).
Thermodynamics → ozone formation endothermic (+142 kJ/mol); F₂ anomalously low bond enthalpy.

14 High-Yield Summary — Top 15 Master these first

NH₃ bond angle 107.8°; drops sharply to ≈ 90° for PH₃ / AsH₃ / SbH₃ / BiH₃.
Stability: NH₃ > … > BiH₃. Reducing power: BiH₃ > … > NH₃. Opposite orders.
H₂O bond angle 104.5°; H₂S 92°; H₂Se 91°; H₂Te 90°. H₂O highest bp (H-bond).
Acidic strength of H₂E: H₂O < H₂S < H₂Se < H₂Te. Opposite of stability.
Halogen oxoacids: HClO₄ > HClO₃ > HClO₂ > HOCl. More O ⇒ stronger acid.
HX acidic order: HF < HCl < HBr < HI. Bond enthalpy dominates.
ΔH_eg: Cl > F, S > O (small-atom repulsion anomaly).
Bond enthalpy X₂: Cl₂ > Br₂ > F₂ > I₂. F₂ anomaly.
Haber: 200 atm, 700 K, Fe/Mo. Contact: V₂O₅, 720 K. Ostwald: Pt/Rh, 500 K.
PCl₅ solid = [PCl₄]⁺[PCl₆]⁻ (sp³ + sp³d²). Gas = TBP (sp³d).
Xe compounds: XeF₂ linear, XeF₄ square-planar, XeF₆ distorted-oct, XeO₃ pyramidal, XeO₄ tetrahedral.
Interhalogen shapes: ClF₃ T-shape, BrF₅ square-pyramidal, IF₇ pentagonal-bipyramidal.
O₃ bond angle 117°, sp²; ozone estimated by 2 KI + O₃ + H₂O → 2 KOH + I₂ + O₂.
Bleaching: Cl₂ oxidation (permanent), SO₂ reduction (temporary).
Basicity of P oxoacids = number of O–H (H₃PO₂ = 1, H₃PO₃ = 2, H₃PO₄ = 3). Reducing needs P–H.

15 Self-Test — 15 MCQs

Q1. Bond angle in NH₃ is:

(a) 90° (b) 104.5° (c) 107.8° (d) 120°

Answer

Q2. The catalyst used in the Contact process is:

(a) Fe + Mo (b) Pt/Rh (c) V₂O₅ (d) Al₂O₃

Answer

Q3. Which is the strongest acid?

(a) HOCl (b) HClO₂ (c) HClO₃ (d) HClO₄

Answer

(d) HClO₄ — highest OS of Cl (+7), best delocalisation of negative charge on ClO₄⁻.

Q4. Shape of XeF₄ is:

(a) Tetrahedral (b) Square planar (c) See-saw (d) Trigonal bipyramidal

Answer

(b) Square planar — sp³d², 2 lone pairs occupy axial positions.

Q5. Reducing power order for Gr 15 hydrides:

(a) NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃ (b) BiH₃ > SbH₃ > AsH₃ > PH₃ > NH₃ (c) NH₃ > BiH₃ > PH₃ (d) PH₃ > NH₃ > AsH₃

Answer

(b) BiH₃ > SbH₃ > AsH₃ > PH₃ > NH₃ — decreasing bond enthalpy makes E–H bond easier to break.

Q6. Basicity of H₃PO₃ is:

(a) 1 (b) 2 (c) 3 (d) 4

Answer

(b) 2 — H₃PO₃ has 2 O–H bonds and 1 P–H bond; only O–H ionise.

Q7. Which halogen has the lowest bond dissociation enthalpy (X₂)?

(a) F₂ (b) Cl₂ (c) Br₂ (d) I₂

Answer

(d) I₂ — 151 kJ/mol. Note F₂ (158 kJ/mol) is anomalously low too but I₂ is the lowest overall.

Q8. The brown ring test for nitrate involves the formation of:

(a) [Fe(H₂O)₆]²⁺ (b) [Fe(H₂O)₅NO]²⁺ (c) [Fe(NO)₆]³⁻ (d) FeNO₃

Answer

(b) [Fe(H₂O)₅NO]²⁺ — brown-ring complex at the H₂SO₄ / test-solution interface.

Q9. Which of the following does NOT exist?

(a) NCl₃ (b) PCl₅ (c) SF₆ (d) NF₅

Answer

(d) NF₅ — N has no d-orbital in the valence shell; cannot expand octet.

Q10. The reddish-brown gas evolved when Cu reacts with conc. HNO₃ is:

(a) NO (b) N₂O (c) NO₂ (d) N₂O₄

Answer

Q11. Which oxide of nitrogen is neutral?

(a) N₂O (b) NO₂ (c) N₂O₃ (d) N₂O₅

Answer

(a) N₂O — neutral (also NO is neutral). N₂O₃, N₂O₅ are acidic anhydrides.

Q12. IF₇ has hybridisation:

(a) sp³d (b) sp³d² (c) sp³d³ (d) sp³

Answer

Q13. The correct order of acidic strength of Gr 16 hydrides is:

(a) H₂O > H₂S > H₂Se > H₂Te (b) H₂Te > H₂Se > H₂S > H₂O (c) H₂S > H₂O > H₂Se > H₂Te (d) H₂Se > H₂S > H₂Te > H₂O

Answer

(b) H₂Te > H₂Se > H₂S > H₂O — E–H bond weakens down the group.

Q14. Which noble gas is used to obtain the lowest temperatures?

(a) He (b) Ne (c) Ar (d) Xe

Answer

(a) He — bp 4.2 K, used in cryogenics.

Q15. Assertion: PCl₅ exists but NCl₅ does not. Reason: N has no d-orbitals in its valence shell.

(a) Both A and R true, R is correct explanation (b) Both true, R is NOT correct explanation (c) A true, R false (d) A false, R true

Answer

(a) Both true, and the absence of d-orbital in N's valence shell (n = 2) is precisely why it cannot expand its octet to form NCl₅.

Card built 2026-07-20 under the "top-score Inorganic" plan. All content aligned strictly to NCERT Class 12 Ch 7 (p-Block Elements). No beyond-NCERT items flagged in this build.

📇 Group-wise Slides — p-Block Groups 15 · 16 · 17 · 18

📅 Built: 2026-07-20 One slide per group

Focused single-slide revision for each of the four p-Block groups on the NEET syllabus. Each slide is self-contained — periodic trends, anomaly of first element, one-liner facts, structures & hybridisation, colours & smells, mnemonics, traps, and a 5-question mini self-test. Use these when revising one group at a time.

🔵 Group 15 — Nitrogen family 🟢 Group 16 — Oxygen family 🟡 Group 17 — Halogens 🟣 Group 18 — Noble gases

Group 15 — Nitrogen Family (N · P · As · Sb · Bi)

Pnictogens · ns² np³ · valence 3, 5

📅 2026-07-20

Trends Down the Group

Property	Trend	Note
Atomic radius	Increases	Big jump N→P (2s→3s)
IE₁	Decreases	Order: N > P > As > Sb < Bi (irregular at Bi)
Electronegativity	Decreases	N most electronegative (3.0)
Metallic character	Increases	N,P non-metal · As,Sb metalloid · Bi metal
MP	Rises to As, then falls to Bi	Peak at As

Oxidation States & Inert-Pair

Common OS: −3, +3, +5. Down the group, +5 stability decreases; +3 becomes more stable (inert-pair effect on 6s²).
Bi³⁺ stable, Bi⁵⁺ strong oxidiser. Similarly PbCl₄ decomposes to PbCl₂ + Cl₂.
N shows +1, +2, +3, +4, +5 in various oxides/oxoacids (NO₂ = +4, HNO₃ = +5, N₂O = +1, etc.).

Anomalous Behaviour of N

Small size · high EN · no d-orbitals · strong pπ–pπ multiple bonds.
Only N forms N≡N triple bond — P, As, Sb, Bi exist as tetrahedral P₄ or polymeric solids.
No NCl₅ / NF₅ (no d-orbitals); PCl₅, PF₅ exist normally.
NH₃ is a strong base (H-bonded, liquefies easily); PH₃/AsH₃ etc. are progressively weaker.
N does not catenate significantly; P/S catenate more readily.

Hydrides & Trends

Property	Order
Thermal stability	NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃
Basicity	NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃
Reducing power	BiH₃ > SbH₃ > AsH₃ > PH₃ > NH₃ (reverse of stability)
Bond angle	NH₃ 107.8° · PH₃ 93.6° · AsH₃ 91.8° · SbH₃ 91.3° · BiH₃ 90°
Boiling point	NH₃ (H-bond) > SbH₃ > AsH₃ > PH₃

Key Preparations (balanced)

NH₃ (Haber): N₂ + 3 H₂ ⇌ 2 NH₃ · 200 atm · 700 K · Fe/Mo

HNO₃ (Ostwald): 4 NH₃ + 5 O₂ → 4 NO + 6 H₂O (Pt/Rh, 500 K); 2 NO + O₂ → 2 NO₂; 3 NO₂ + H₂O → 2 HNO₃ + NO

PCl₃ hydrolysis: PCl₃ + 3 H₂O → H₃PO₃ + 3 HCl

PCl₅ hydrolysis: PCl₅ + 4 H₂O → H₃PO₄ + 5 HCl

Brown-ring test: [Fe(H₂O)₅NO]²⁺ (nitrate detection at H₂SO₄ interface)

Structures & Hybridisation

Species	Hyb	Shape	Bond angle
NH₃	sp³	Trigonal pyramidal	107.8°
PCl₅ (g)	sp³d	Trigonal bipyramidal	90° / 120°
PCl₅ (s)	[PCl₄]⁺ sp³ + [PCl₆]⁻ sp³d²	Td + Oct	109.5° / 90°
P₄	sp³	Tetrahedral cluster	60° P–P–P
P₄O₁₀	sp³	Cage + 4 terminal P=O	—

P Oxoacids (basicity from O–H count)

Acid	Formula	OS of P	Basicity	Reducing?
Hypophosphorous	H₃PO₂	+1	Monobasic	Strong (2 P–H)
Phosphorous	H₃PO₃	+3	Dibasic	Yes (1 P–H)
Orthophosphoric	H₃PO₄	+5	Tribasic	No

Colours & Physical Cues

NO — colourless · NO₂ — brown · N₂O₃ — blue liquid · N₂O — laughing gas (colourless).
White P (P₄) — waxy, garlic smell, glows in dark (chemiluminescence), poisonous.
Red P — dark red, polymeric, non-poisonous, no glow.
NH₃ — pungent smell, white fumes with HCl (test).

Mnemonic — Order of Group 15: "Nothing Plus Ask Sb Billy" → N, P, As, Sb, Bi.

Bond angle drop: NH₃ = 107.8°, all others ≈ 90° (say "N is odd; rest is 90").

Trap: H₃PO₃ is dibasic (not tribasic!) — the P–H bond doesn't ionise. Similarly H₃PO₂ is monobasic.

Trap: PCl₅ gas = TBP (sp³d); PCl₅ solid = [PCl₄]⁺[PCl₆]⁻ (sp³ + sp³d²) — different structures.

Mini Self-Test (5 Q)

Q1. Bond angle in PH₃ ≈

(a) 90° (b) 93.6° (c) 107.8° (d) 120°

Answer

(b) 93.6° — much smaller than NH₃'s 107.8° due to poor sp³ hybridisation in larger P.

Q2. Which does NOT exist?

(a) NCl₃ (b) NF₃ (c) NCl₅ (d) NH₃

Answer

Q3. Reducing power of Gr 15 hydrides is largest for:

(a) NH₃ (b) PH₃ (c) AsH₃ (d) BiH₃

Answer

(d) BiH₃ — bond enthalpy decreases down the group, so BiH₃ releases H atoms most easily.

Q4. Basicity of H₃PO₂ is

(a) 1 (b) 2 (c) 3 (d) 4

Answer

(a) 1 — only 1 O–H bond; the 2 P–H bonds don't ionise.

Q5. Haber process operating conditions:

(a) 200 atm, 700 K, Fe/Mo (b) 1 atm, 300 K, Pt (c) 100 atm, 500 K, V₂O₅ (d) 500 atm, 900 K, Ni

Answer

(a) 200 atm, 700 K, Fe catalyst + Mo promoter.

Group 16 — Oxygen Family / Chalcogens (O · S · Se · Te · Po)

ns² np⁴ · valence 2, 4, 6

📅 2026-07-20

Trends Down the Group

Property	Trend	Note
Atomic radius	Increases	Largest jump O → S
IE₁	Decreases	O less than N — half-filled 2p³ of N is more stable
Electronegativity	Decreases	O = 3.5 (2nd only to F)
ΔH_eg (electron gain)	Anomalous	\|ΔH_eg\| of S > O (O small ⇒ e⁻–e⁻ repulsion)
Metallic character	Increases	O,S non-metal · Se,Te metalloid · Po metal
MP / BP	Increases	O₂ gas → Po solid

Oxidation States

Common: −2, +2, +4, +6. Down the group +6 stability decreases; Po prefers +2/+4.
Oxygen only shows −2 (and −1 in peroxide, +2 in OF₂, −½ in superoxide). No expanded octet (no OF₆).

Anomalous Behaviour of O

Small size · high EN · no d-orbitals · strong pπ–pπ bonds.
O₂ is a gas (S₈ solid, ring structure). H₂O is liquid due to H-bonding; H₂S is a gas.
Only −2 as common OS (no +4/+6). No expanded-octet compounds.

Hydrides & Trends

Property	Order
Thermal stability	H₂O > H₂S > H₂Se > H₂Te > H₂Po
Acidic strength	H₂O < H₂S < H₂Se < H₂Te (opposite of stability)
Reducing power	H₂O < H₂S < H₂Se < H₂Te
Bond angle	H₂O 104.5° · H₂S 92° · H₂Se 91° · H₂Te 90°
Boiling point	H₂O (H-bond, anomaly) > H₂Te > H₂Se > H₂S

Key Preparations (balanced)

H₂SO₄ (Contact): S + O₂ → SO₂; 2 SO₂ + O₂ ⇌ 2 SO₃ (V₂O₅, 720 K); SO₃ + H₂SO₄ → H₂S₂O₇ (oleum); + H₂O → 2 H₂SO₄

Ozone (silent electric discharge): 3 O₂ ⇌ 2 O₃ · ΔH = +142 kJ/mol (endothermic)

Ozone estimation: 2 KI + O₃ + H₂O → 2 KOH + I₂ + O₂

Structures & Hybridisation

Species	Hyb	Shape	Bond angle
O₃	sp²	Bent (V-shape), resonance	117°
SO₂	sp²	Bent	119.5°
SO₃	sp²	Trigonal planar	120°
H₂SO₄	sp³	Tetrahedral	109.5°
SF₆	sp³d²	Octahedral (very stable, inert)	90°
SF₄	sp³d	See-saw (1 LP equatorial)	—

S Oxoacids

Name	Formula	OS of S	Notes
Sulphurous	H₂SO₃	+4	Dibasic; unstable (mostly aq. only)
Sulphuric	H₂SO₄	+6	Dibasic, strong; dehydrating & oxidising
Pyrosulphuric (oleum)	H₂S₂O₇	+6	From SO₃ + H₂SO₄
Peroxydisulphuric (Marshall's)	H₂S₂O₈	+6	Contains –O–O– bond

Colours & Physical Cues

SO₂ — colourless, pungent, suffocating smell; H₂S — rotten-egg smell.
O₃ — pale blue gas, sharp chlorine-like smell.
Rhombic S₈ — yellow, stable; monoclinic S₈ — pale yellow, above 96 °C.
SO₂ bleaches by reduction (temporary); Cl₂ bleaches by oxidation (permanent).

Mnemonic — Order of Group 16: "Our School Selects Tens Points" → O, S, Se, Te, Po.

Contact vs Haber: Contact = SO₂ oxidation, V₂O₅, 720 K. Haber = N₂+H₂, Fe/Mo, 200 atm, 700 K.

Trap: ΔH_eg magnitude — Cl > F, S > O (not the other way!) — small atom means e⁻–e⁻ repulsion.

Trap: H₂O has highest boiling point in Gr 16 but LOWEST acidity (H-bond dominates in bp, bond enthalpy dominates in acidity).

Mini Self-Test (5 Q)

Q1. Ozone bond angle:

(a) 104.5° (b) 109.5° (c) 117° (d) 120°

Answer

Q2. Order of acidic strength of Gr 16 hydrides:

(a) H₂O > H₂S > H₂Se > H₂Te (b) H₂Te > H₂Se > H₂S > H₂O (c) H₂S > H₂O > H₂Se (d) H₂O = H₂S

Answer

(b) H₂Te > H₂Se > H₂S > H₂O — E–H bond weakens down the group.

Q3. Contact process catalyst is:

(a) Fe/Mo (b) V₂O₅ (c) Pt/Rh (d) Ni

Answer

(b) V₂O₅ at 720 K for 2 SO₂ + O₂ ⇌ 2 SO₃.

Q4. SF₄ shape is:

(a) Tetrahedral (b) See-saw (c) Octahedral (d) Square planar

Answer

(b) See-saw — sp³d with 1 lone pair in equatorial position.

Q5. Bleaching by SO₂ is:

(a) Oxidation, permanent (b) Reduction, temporary (c) Oxidation, temporary (d) Reduction, permanent

Answer

(b) Reduction, temporary — colour returns on standing (re-oxidation by air).

Group 17 — Halogens (F · Cl · Br · I · At)

ns² np⁵ · valence 1 (with variable OS via d)

📅 2026-07-20

Trends Down the Group

Property	Trend	Note
Atomic radius	Increases	Smallest of the period (across); increases down
IE₁	Decreases	Halogens have highest IE₁ in period (except noble)
Electronegativity	Decreases	F = 4.0 (highest of all elements)
ΔH_eg (electron gain)	Anomalous	\|ΔH_eg\| of Cl > F — F small, e⁻–e⁻ repulsion in 2p
Physical state	Trend	F₂ gas · Cl₂ gas · Br₂ liquid · I₂ solid
Bond enthalpy of X₂	Anomalous	Cl₂ > Br₂ > F₂ > I₂ (F₂ low due to lone-pair repulsion)

Oxidation States

F: only −1 (no d-orbitals, most EN — never positive).
Cl, Br, I: −1, +1, +3, +5, +7 (use d-orbitals for higher OS).
+7 is the highest common OS (HClO₄, IF₇, HIO₄).

Anomalous Behaviour of F

Smallest halogen · most EN of all elements · no d-orbitals in valence shell.
Only shows −1; never positive OS.
F₂ bond enthalpy anomalously low (158 kJ/mol) due to lone-pair repulsion in tiny F₂.
HF liquid due to H-bonding; other HX gases.
No oxoacids of +7 type; only limited oxoacids known for F.
Strongest oxidiser of all elements.

HX & Halogen Trends

Property	Order
Oxidising power (X₂)	F₂ > Cl₂ > Br₂ > I₂
Reducing power (X⁻)	I⁻ > Br⁻ > Cl⁻ > F⁻
HX bond dissociation enthalpy	HF > HCl > HBr > HI
HX acidic strength (aq.)	HF < HCl < HBr < HI (bond enthalpy dominates, not EN!)
HX boiling point	HF > HI > HBr > HCl (HF H-bonded, anomaly)
Oxoacid acidity (same X)	HXO < HXO₂ < HXO₃ < HXO₄
Oxoacid acidity (same +1 OS)	HOCl > HOBr > HOI

Key Preparations (balanced)

Cl₂ (Deacon): 4 HCl + O₂ → 2 Cl₂ + 2 H₂O (CuCl₂, 723 K)

Cl₂ (lab, MnO₂): MnO₂ + 4 HCl → MnCl₂ + Cl₂ + 2 H₂O

Cl₂ + cold, dil. NaOH: Cl₂ + 2 NaOH → NaCl + NaOCl + H₂O

Cl₂ + hot, conc. NaOH: 3 Cl₂ + 6 NaOH → 5 NaCl + NaClO₃ + 3 H₂O

Bleaching powder: 2 Ca(OH)₂ + 2 Cl₂ → Ca(OCl)₂ + CaCl₂ + 2 H₂O

Interhalogens & Structures

Species	Hyb	Shape	Bond angle
ClF₃	sp³d	T-shape	87.5°
BrF₃	sp³d	T-shape	—
IF₅	sp³d²	Square pyramidal (1 LP)	—
BrF₅	sp³d²	Square pyramidal	90°
IF₇	sp³d³	Pentagonal bipyramidal (0 LP)	72° / 90°

Colours & Physical Cues

F₂ — pale yellow gas · Cl₂ — greenish-yellow gas · Br₂ — reddish-brown liquid · I₂ — violet solid, violet vapour.
Bleaching powder — pale yellow, chlorine-like smell.
Aqua regia (3 HCl : 1 HNO₃) — orange fumes, dissolves Au and Pt.

Mnemonic — Halogens: "Fast Clever Brown Indian Athlete" → F, Cl, Br, I, At.

Oxoacid acidity: "More O = more acid" (delocalisation of charge on conjugate base).

Trap: HF is the weakest HX acid despite F being most EN — because bond enthalpy dominates, not EN.

Trap: F₂ has lowest bond enthalpy (not highest!) — lone-pair repulsion in the tiny F₂ molecule.

Mini Self-Test (5 Q)

Q1. Correct order of acidic strength of HX:

(a) HF > HCl > HBr > HI (b) HI > HBr > HCl > HF (c) HCl > HF > HBr > HI (d) All equal

Answer

(b) HI is strongest; HF is weakest — bond enthalpy decreases down the group.

Q2. Shape of IF₇ is:

(a) Tetrahedral (b) Octahedral (c) Pentagonal bipyramidal (d) Trigonal bipyramidal

Answer

Q3. The strongest halogen oxoacid is:

(a) HOCl (b) HClO₂ (c) HClO₃ (d) HClO₄

Answer

(d) HClO₄ — Cl is in +7; charge on ClO₄⁻ delocalised over 4 O atoms.

Q4. Which halogen shows only −1 oxidation state?

(a) Cl (b) Br (c) I (d) F

Answer

(d) F — most electronegative and has no d-orbitals in the valence shell.

Q5. Product of Cl₂ + hot conc. NaOH:

(a) NaCl + NaOCl (b) NaCl + NaClO₃ (c) NaClO₄ only (d) Cl₂ dissolves without reaction

Answer

(b) 3 Cl₂ + 6 NaOH → 5 NaCl + NaClO₃ + 3 H₂O (disproportionation).

Group 18 — Noble Gases (He · Ne · Ar · Kr · Xe · Rn)

ns² np⁶ (He: 1s²) · closed shell · monatomic

📅 2026-07-20

Trends Down the Group

Property	Trend	Note
Atomic radius	Increases	Largest in each period (van der Waals)
IE₁	Decreases	Still highest in period; He has the highest IE₁ of all elements
Boiling point	Increases	He 4.2 K (lowest of all elements) · Rn ~ 211 K
Chemical reactivity	Increases	Only Xe (and limited Kr) form compounds; He, Ne, Ar do not
Abundance in air	Ar > Ne > He > Kr > Xe	Ar ≈ 0.93 % of dry air

Why Noble Gases Are Inert

Completely filled valence shell (ns²np⁶; He is 1s²) — no tendency to gain, lose or share electrons.
Very high IE₁ — highest in each period.
Positive electron gain enthalpy — do not accept electrons.
Reactivity emerges only for Xe (and marginally Kr) because larger size ⇒ lower IE ⇒ can be forced to bond with the most electronegative element (F, O).

Xenon Compounds — Preparations (balanced)

XeF₂: Xe + F₂ → XeF₂ (400 °C, 1 atm, Xe:F₂ = 1:5)

XeF₄: Xe + 2 F₂ → XeF₄ (400 °C, 6 atm, Xe:F₂ = 1:5)

XeF₆: Xe + 3 F₂ → XeF₆ (300 °C, 60–70 atm, Xe:F₂ = 1:20)

Hydrolysis of XeF₆: XeF₆ + 3 H₂O → XeO₃ + 6 HF

Partial hydrolysis: XeF₆ + H₂O → XeOF₄ + 2 HF; 2 XeF₆ + SiO₂ → 2 XeOF₄ + SiF₄

XeO₄ (rare): Ba₃XeO₆ + H₂SO₄ → XeO₄ + …

Structures & Hybridisation

Species	Hyb	Shape	LP on Xe	Bond angle
XeF₂	sp³d	Linear	3	180°
XeF₄	sp³d²	Square planar	2	90°
XeF₆	sp³d³	Distorted octahedral	1	—
XeOF₄	sp³d²	Square pyramidal	1	—
XeO₃	sp³	Trigonal pyramidal	1	—
XeO₄	sp³	Tetrahedral	0	109.5°

Uses (NCERT-listed)

He — cryogenics, filling weather balloons (safer than H₂), diving mixtures (heliox), MRI-magnet coolant.
Ne — advertising signs (red-orange glow), high-voltage indicators, aircraft lighting.
Ar — inert atmosphere in welding & metallurgy; fill filament bulbs to prevent oxidation.
Kr — high-intensity lamps for airport runways.
Xe — high-intensity photographic flash lamps, arc lamps.
Rn — radioactive; formerly used in cancer radiotherapy.

Colours & Physical Cues

All noble gases are colourless, odourless, tasteless, monatomic gases.
Xenon fluorides: colourless solids (XeF₂, XeF₄, XeF₆).
XeO₃ — colourless explosive solid; XeO₄ — colourless gas, explosive.
Neon signs glow red-orange when a discharge is passed through Ne.

Mnemonic — Noble gases: "Help Needed At Krishna's Xerography Rn" → He, Ne, Ar, Kr, Xe, Rn.

Xe fluoride LP count: "3, 2, 1 count-down" — XeF₂ has 3 LP, XeF₄ has 2 LP, XeF₆ has 1 LP.

Trap: He does NOT solidify at atmospheric pressure — needs applied pressure. Boiling point 4.2 K is the lowest of any element.

Trap: XeF₄ is square planar (not tetrahedral!) — 2 lone pairs occupy axial positions in sp³d² geometry.

Mini Self-Test (5 Q)

Q1. Shape of XeF₂ is:

(a) Linear (b) Bent (c) Square planar (d) T-shape

Answer

(a) Linear — sp³d with 3 lone pairs occupying equatorial positions of TBP.

Q2. Which noble gas has the lowest boiling point?

(a) He (b) Ne (c) Ar (d) Xe

Answer

(a) He — 4.2 K (lowest boiling point of any element).

Q3. Product of XeF₆ + H₂O (complete hydrolysis):

(a) XeO₃ + HF (b) XeO₄ + HF (c) Xe + O₂ (d) XeOF₄ + HF

Answer

(a) XeF₆ + 3 H₂O → XeO₃ + 6 HF (complete hydrolysis). Partial hydrolysis gives XeOF₄.

Q4. Number of lone pairs on central Xe in XeF₆:

(a) 0 (b) 1 (c) 2 (d) 3

Answer

(b) 1 — sp³d³ hybridisation, 6 bond pairs + 1 lone pair ⇒ distorted octahedral.

Q5. Which noble gas is used in fluorescent-lamp red-orange signs?

(a) He (b) Ne (c) Ar (d) Kr

Answer

(b) Ne — the classic "neon-sign" red-orange glow comes from Ne discharge.

All four slides built 2026-07-20 under the "top-score Inorganic" plan. Content strictly from NCERT Class 12 Ch 7. Use these when revising one group at a time; the combined pack (above) is the cross-group overview.

Property	Nitrogen (N)	Phosphorus (P)
Allotropy	Only N₂	White, red, black
Bond type	pπ-pπ multiple bonds	Mostly single bonds; uses d-orbitals for π
Catenation	No	Yes (P₄ tetrahedron, polyphosphates)
Hydride basicity	NH₃ strongly basic	PH₃ weakly basic
Halides	NCl₃, NF₃ exist	PCl₃, PCl₅ (uses d-orbital)
Max oxidation state	+5 (HNO₃, NO₃⁻)	+5 (uses d-orbital)

Property	Oxygen	Sulphur
State at STP	Gas (O₂, O₃)	Solid (S₈ ring)
Bond type	pπ-pπ double bond (O=O)	Single bonds, S₈ ring
Electronegativity	3.5	2.5
Acid strength of hydride	H₂O weak	H₂S stronger
Catenation	Limited	Extensive (polysulphides)
Max OS	+2 (OF₂)	+6 (SF₆, H₂SO₄)

Property	F	Cl	Br	I
Phase at STP	Gas (pale yellow)	Gas (yellow-green)	Liquid (red-brown)	Solid (purple-black)
Bond dissociation (X-X)	Lower (F-F anomaly)	Highest	Medium	Lowest
Oxidising power	Strongest	High	Lower	Lowest
Electronegativity	Highest (4.0)	3.0	2.8	2.5
Hydride (HX) acidity	Weakest (HF)	Stronger	Stronger	Strongest (HI)

Group	Higher OS stable in	Lower OS stable in
13 (Tl)	Lighter (B, Al, Ga): +3	Heavier (Tl): +1
14 (Pb)	Lighter (C, Si): +4	Heavier (Pb): +2
15 (Bi)	Lighter (N, P): +5	Heavier (Bi): +3

Pair	Common property	Why
Li ↔ Mg	Both form nitrides, hard carbonates	Similar charge density
Be ↔ Al	Amphoteric oxides; form covalent halides	Similar polarising power
B ↔ Si	Similar oxides (acidic), form similar halides	Similar size and EN

Acid	Cl OS	Acid strength	Oxidising power
HClO (hypochlorous)	+1	Weakest	Strongest
HClO₂ (chlorous)	+3	Weak	Strong
HClO₃ (chloric)	+5	Strong	Moderate
HClO₄ (perchloric)	+7	Strongest	Weakest

Oxidiser	E° (V)	Typical use
F₂	+2.87	Strongest known oxidiser
O₃	+2.07	Bleaching, oxidising organic
MnO₄⁻ (acidic)	+1.51	Permanganate titrations
Cr₂O₇²⁻ (acidic)	+1.33	Dichromate titrations
O₂	+1.23	Common

Element	Major allotropes	Differences
P (phosphorus)	White P₄ (tetrahedral, reactive); Red P (polymeric, stable)	White ignites in air; Red doesn't
S (sulphur)	Rhombic (yellow, stable below 95.6°C); Monoclinic (above 95.6°C)	Both contain S₈ rings
S	Plastic sulphur	Long polymeric chains; metastable

Property	He	Ne	Ar	Kr	Xe	Rn
Atomic number	2	10	18	36	54	86
Boiling point (K)	4.2	27	87	120	165	211
Compounds known?	No	No	Few	Few	Many (XeF₂, XeOF₄)	Few

Property	NH₃	PH₃	AsH₃
Boiling point (°C)	−33	−87	−55 (rises due to mass)
H-bonding	Yes	No	No
Basic strength	Strong	Weak	Very weak
Bond angle	107°	93.5°	91.8°
Reducing power	Weakest	Strong	Stronger

The Cheat Sheet Dashboard

Group 13 — Boron Family

Group 14 — Carbon Family

Anomalous Behaviour (B & C)

Inert Pair Effect

Diagonal Relationship

Interactive Periodic Trends

Inert-Pair Effect Explorer

Mentor's Tip — Inert Pair Rule

Quick Reactions & Key Compounds

Must-Memorise — for Aamirah

1Group Configurations & Character

2Trend Orders (memorise verbatim)

3Acidity Orders

4Catenation & Bond Strengths

5Hybridisation Cheat-Sheet

6Key Compounds & Their Formulas

7Inert-Pair Trio (oxidiser vs reducer)

8Anomalies & “Doesn’t Exist”

9Numbers Worth Memorising

10Reactions to Recall in One Line

Quick-Recall Flashcards

Easy Explanation — Line by Line

Exceptions to Remember

Examples & Reference Data

Solved Problems — Explained & Worked

50 NEET / AIPMT-Pattern PYQs — Solved

25 JEE-Pattern PYQs — Solved

🎯 p-Block Revision Pack — Groups 15, 16, 17, 18

📇 Group-wise Slides — p-Block Groups 15 · 16 · 17 · 18

⚖️ Quick Comparisons — Side-by-Side Reference

VS Group 15: Nitrogen vs Phosphorus (anomalous N)

VS Group 16: Oxygen vs Sulphur

VS Group 17: Halogens trends (F → I)

VS Inert pair effect: stability of oxidation states

VS Oxoacids of chlorine — strength & OS

VS Diagonal relationships

VS Oxidising power: F₂ vs O₃ vs KMnO₄

VS Allotropes of phosphorus and sulphur

VS Noble gases: Group 18 properties down the group

VS NH₃ vs PH₃ vs AsH₃