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P-Block Elements Formulas for JEE 2026
p-Block Elements is an important chapter in JEE Chemistry and is known for being quite scoring if prepared well. It mainly deals with the elements from Groups 13–18 of the periodic table. In this topic, students learn about the properties and reactions of key elements such as boron, carbon, nitrogen, oxygen, halogens, and noble gases. Understanding these elements helps students see how their compounds are formed and how they behave in different chemical reactions.
The chapter also explains the structures, preparation methods, and important compounds of these elements, which are often asked in JEE exams. Since many questions are based on concepts and reactions, regular revision is very important. For quick and easy revision, students can also refer to a well-organized JEE Mains Chemistry Formula PDF, which helps them review important reactions and key points during their preparation.
Group 13: Boron Family Formulas for JEE
Overview of p-Block Groups
| Group | Name | Valence Config | Elements |
|---|---|---|---|
| 13 | Boron family | $$ns^2\,np^1$$ | B, Al, Ga, In, Tl |
| 14 | Carbon family | $$ns^2\,np^2$$ | C, Si, Ge, Sn, Pb |
| 15 | Pnictogens | $$ns^2\,np^3$$ | N, P, As, Sb, Bi |
| 16 | Chalcogens | $$ns^2\,np^4$$ | O, S, Se, Te, Po |
| 17 | Halogens | $$ns^2\,np^5$$ | F, Cl, Br, I, At |
| 18 | Noble gases | $$ns^2\,np^6$$ | He, Ne, Ar, Kr, Xe, Rn |
Definition: Inert Pair Effect
The reluctance of the $$s$$-electrons of the valence shell to participate in bonding in heavier p-block elements. As we go down a group, the lower oxidation state becomes more stable. Example: Tl prefers +1 over +3; Pb prefers +2 over +4.
Boron Compounds
Borax (Na$$_2$$B$$_4$$O$$_7$$ · 10H$$_2$$O)
- Dissolves in water to give alkaline solution: $$\text{Na}_2\text{B}_4\text{O}_7 + 7\text{H}_2\text{O} \to 2\text{NaOH} + 4\text{H}_3\text{BO}_3$$
- Borax bead test: On heating: $$\text{Na}_2\text{B}_4\text{O}_7 \xrightarrow{\Delta} 2\text{NaBO}_2 + \text{B}_2\text{O}_3$$ (transparent glass bead)
Boric Acid (H$$_3$$BO$$_3$$)
- Weak, monobasic Lewis acid (not Bronsted acid)
- Accepts OH$$^-$$ from water: $$\text{B(OH)}_3 + \text{H}_2\text{O} \rightleftharpoons \text{B(OH)}_4^- + \text{H}^+$$
- On heating: H$$_3$$BO$$_3$$ → HBO$$_2$$ (metaboric acid) → B$$_2$$O$$_3$$ (boron trioxide)
Important Note
Boric acid is a Lewis acid, not a protonic (Bronsted) acid. It accepts an OH$$^-$$ from water rather than donating H$$^+$$. This distinction is commonly tested in JEE.
Diborane (B$$_2$$H$$_6$$)
- Contains 4 terminal B–H bonds (normal 2c-2e bonds)
- Contains 2 bridging B–H–B bonds (3-centre 2-electron bonds, "banana bonds")
- Each boron is $$sp^3$$ hybridised; molecule is electron deficient
- With water: $$\text{B}_2\text{H}_6 + 6\text{H}_2\text{O} \to 2\text{H}_3\text{BO}_3 + 6\text{H}_2\uparrow$$
BF$$_3$$ vs AlCl$$_3$$
- BF$$_3$$: $$sp^2$$ hybridised, trigonal planar, strong Lewis acid. Does not dimerise (F provides $$p\pi$$–$$p\pi$$ back bonding)
- AlCl$$_3$$: Exists as dimer Al$$_2$$Cl$$_6$$ in vapour phase (bridging chlorines). Strong Lewis acid, catalyst in Friedel-Crafts reactions. Each Al is $$sp^3$$ in the dimer.
Group 14: Carbon Family Formulas for JEE
Definition: Catenation
The ability of an atom to form bonds with other atoms of the same element, creating long chains, branched chains, or rings. Carbon has the highest catenation tendency (C–C bond = 348 kJ/mol). Order: C ≫ Si > Ge > Sn > Pb.
Allotropes of Carbon
| Allotrope | Hybridisation | Structure | Properties |
|---|---|---|---|
| Diamond | $$sp^3$$ | 3D tetrahedral network | Hardest substance, insulator |
| Graphite | $$sp^2$$ | Layered hexagonal sheets | Soft, lubricant, conductor |
| Fullerene (C$$_{60}$$) | $$sp^2$$ | Spherical cage | Soluble in organic solvents |
Graphite conducts because delocalised $$p$$-electrons are mobile across layers. It is soft because layers slide over each other (weak van der Waals forces).
Carbon Monoxide (CO)
- Colourless, odourless, highly toxic (binds to haemoglobin 200× more strongly than O$$_2$$)
- Strong reducing agent: $$\text{Fe}_2\text{O}_3 + 3\text{CO} \to 2\text{Fe} + 3\text{CO}_2$$ (blast furnace)
- Acts as a ligand (e.g., [Ni(CO)$$_4$$])
- Triple bond: $$:\text{C} \equiv \text{O}:$$ (isoelectronic with N$$_2$$)
Carbon Dioxide (CO$$_2$$)
- Linear molecule ($$sp$$ hybridised), O=C=O, bond angle 180°
- Turns lime water milky: $$\text{Ca(OH)}_2 + \text{CO}_2 \to \text{CaCO}_3\downarrow + \text{H}_2\text{O}$$
- Acidic oxide: $$\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3$$ (weak)
- Does not support combustion (except Mg burns in CO$$_2$$)
- Solid CO$$_2$$ = "dry ice" (sublimes at $$-78$$°C)
Group 15: Nitrogen Family Formulas for JEE
Ammonia (NH$$_3$$)
Haber process: $$\text{N}_2 + 3\text{H}_2 \xrightarrow[\text{200 atm, Fe}]{\text{700 K}} 2\text{NH}_3$$
- Trigonal pyramidal ($$sp^3$$, one lone pair), bond angle ≈ 107°
- Weak base: $$\text{NH}_3 + \text{H}_2\text{O} \rightleftharpoons \text{NH}_4^+ + \text{OH}^-$$
- Lewis base: forms complexes like [Cu(NH$$_3$$)$$_4$$]$$^{2+}$$ (deep blue)
- Catalytic oxidation: $$4\text{NH}_3 + 5\text{O}_2 \xrightarrow{\text{Pt/Rh}} 4\text{NO} + 6\text{H}_2\text{O}$$
- Test: Turns moist red litmus blue; white fumes with HCl ($$\text{NH}_4\text{Cl}$$)
Nitric Acid (HNO$$_3$$) — Ostwald Process
$$4\text{NH}_3 + 5\text{O}_2 \xrightarrow{\text{Pt, 500K}} 4\text{NO} + 6\text{H}_2\text{O}$$
$$2\text{NO} + \text{O}_2 \to 2\text{NO}_2$$
$$3\text{NO}_2 + \text{H}_2\text{O} \to 2\text{HNO}_3 + \text{NO}$$
- Strong acid, powerful oxidising agent
- Aqua regia = 3 parts conc. HCl + 1 part conc. HNO$$_3$$ (dissolves Au and Pt)
- With Cu (dilute): $$3\text{Cu} + 8\text{HNO}_3 \to 3\text{Cu(NO}_3)_2 + 2\text{NO}\uparrow + 4\text{H}_2\text{O}$$
- With Cu (conc.): $$\text{Cu} + 4\text{HNO}_3 \to \text{Cu(NO}_3)_2 + 2\text{NO}_2\uparrow + 2\text{H}_2\text{O}$$
Phosphorus Compounds
Allotropes of Phosphorus
| Allotrope | Structure | Properties |
|---|---|---|
| White P (P$$_4$$) | Tetrahedral | Waxy, poisonous, glows in dark, most reactive |
| Red P | Polymeric chains | Non-poisonous, less reactive |
| Black P | Layered (like graphite) | Least reactive, semiconductor |
Phosphorus Halides
- PCl$$_3$$: $$sp^3$$, trigonal pyramidal. Hydrolyses: $$\text{PCl}_3 + 3\text{H}_2\text{O} \to \text{H}_3\text{PO}_3 + 3\text{HCl}$$
- PCl$$_5$$: $$sp^3d$$, trigonal bipyramidal (vapour). Axial bonds longer/weaker. In solid: [PCl$$_4$$]$$^+$$[PCl$$_6$$]$$^-$$ (ionic). Hydrolyses: $$\text{PCl}_5 + 4\text{H}_2\text{O} \to \text{H}_3\text{PO}_4 + 5\text{HCl}$$
Oxoacids of Phosphorus
| Oxoacid | Formula | Basicity | P–H Bonds |
|---|---|---|---|
| Hypophosphorous acid | H$$_3$$PO$$_2$$ | Monobasic | 2 |
| Phosphorous acid | H$$_3$$PO$$_3$$ | Dibasic | 1 |
| Phosphoric acid | H$$_3$$PO$$_4$$ | Tribasic | 0 |
Key rule: Only H atoms bonded to O (as O–H) are acidic. H atoms bonded directly to P (as P–H) are not acidic.
Group 16: Oxygen Family Formulas for JEE
Ozone (O$$_3$$)
- Pale blue gas, pungent smell; diamagnetic
- Angular shape ($$sp^2$$), bond angle ≈ 117°
- Powerful oxidising agent: $$\text{O}_3 \to \text{O}_2 + [\text{O}]$$
- Detected by: turns moist KI-starch paper blue
- $$\text{O}_3 + 2\text{KI} + \text{H}_2\text{O} \to 2\text{KOH} + \text{I}_2 + \text{O}_2$$
Sulphuric Acid — Contact Process
$$\text{S} + \text{O}_2 \to \text{SO}_2$$
$$2\text{SO}_2 + \text{O}_2 \xrightarrow[\text{720 K}]{\text{V}_2\text{O}_5} 2\text{SO}_3$$
$$\text{SO}_3 + \text{H}_2\text{SO}_4 \to \text{H}_2\text{S}_2\text{O}_7$$ (oleum)
$$\text{H}_2\text{S}_2\text{O}_7 + \text{H}_2\text{O} \to 2\text{H}_2\text{SO}_4$$
- Strong dibasic acid; powerful dehydrating agent and oxidising agent
- Chars sugar: $$\text{C}_{12}\text{H}_{22}\text{O}_{11} \xrightarrow{\text{H}_2\text{SO}_4} 12\text{C} + 11\text{H}_2\text{O}$$
- Hot conc. with Cu: $$\text{Cu} + 2\text{H}_2\text{SO}_4 \to \text{CuSO}_4 + \text{SO}_2\uparrow + 2\text{H}_2\text{O}$$
Oxoacids of Sulphur
| Oxoacid | Formula | Oxidation State of S |
|---|---|---|
| Sulphurous acid | H$$_2$$SO$$_3$$ | +4 |
| Sulphuric acid | H$$_2$$SO$$_4$$ | +6 |
| Thiosulphuric acid | H$$_2$$S$$_2$$O$$_3$$ | +2 (average) |
| Peroxodisulphuric acid | H$$_2$$S$$_2$$O$$_8$$ | +6 |
| Oleum | H$$_2$$S$$_2$$O$$_7$$ | +6 |
Group 17: Halogens Formulas for JEE
Properties of Hydrogen Halides
| Property | HF | HCl | HBr | HI |
|---|---|---|---|---|
| Bond strength | Strongest | ↓ | ↓ | Weakest |
| Acidic strength | Weakest | ↑ | ↑ | Strongest |
| Reducing power | Weakest | ↑ | ↑ | Strongest |
| Thermal stability | Most stable | ↓ | ↓ | Least stable |
HF is a weak acid (strong H–F bond, 568 kJ/mol); all others are strong acids.
Important: HF is Unique
- Weak acid despite F being the most electronegative element (very strong H–F bond)
- Attacks glass: $$\text{SiO}_2 + 4\text{HF} \to \text{SiF}_4 + 2\text{H}_2\text{O}$$ (glass etching)
- Forms hydrogen bonds → anomalously high boiling point
Interhalogen Compounds
| Type | Examples | Hybridisation | Shape |
|---|---|---|---|
| XX' | ClF, BrF, ICl, IBr | $$sp^3$$ | Linear |
| XX'$$_3$$ | ClF$$_3$$, BrF$$_3$$, ICl$$_3$$ | $$sp^3d$$ | T-shaped |
| XX'$$_5$$ | BrF$$_5$$, IF$$_5$$ | $$sp^3d^2$$ | Square pyramidal |
| XX'$$_7$$ | IF$$_7$$ | $$sp^3d^3$$ | Pentagonal bipyramidal |
Oxoacids of Chlorine
| Oxoacid | Formula | Oxidation State | Acidic Strength |
|---|---|---|---|
| Hypochlorous acid | HOCl | +1 | Weakest |
| Chlorous acid | HClO$$_2$$ | +3 | ↑ |
| Chloric acid | HClO$$_3$$ | +5 | ↑ |
| Perchloric acid | HClO$$_4$$ | +7 | Strongest |
Trend: More oxygen atoms → stronger acid (negative charge delocalised over more O atoms).
Group 18: Noble Gases Formulas for JEE
Compounds of Xenon with Fluorine
| Compound | Hybridisation | Shape | Lone Pairs |
|---|---|---|---|
| XeF$$_2$$ | $$sp^3d$$ | Linear | 3 |
| XeF$$_4$$ | $$sp^3d^2$$ | Square planar | 2 |
| XeF$$_6$$ | $$sp^3d^3$$ | Distorted octahedral | 1 |
| XeO$$_3$$ | $$sp^3$$ | Pyramidal | 1 |
Hydrolysis:
- $$\text{XeF}_2 + \text{H}_2\text{O} \to \text{Xe} + 2\text{HF} + \frac{1}{2}\text{O}_2$$
- $$\text{XeF}_6 + 3\text{H}_2\text{O} \to \text{XeO}_3 + 6\text{HF}$$
Important Note
Among noble gases, only Kr and Xe form compounds. He, Ne, and Ar do not form stable compounds. Kr forms only KrF$$_2$$ (unstable). Xenon forms the widest range of compounds because its outer electrons (5th shell) are loosely held.
Key Trends Across p-Block Quick Reference for JEE
Important Trends Across p-Block Groups
- Inert pair effect: Stability of lower oxidation state increases down each group (Tl$$^+$$ > Tl$$^{3+}$$; Pb$$^{2+}$$ > Pb$$^{4+}$$)
- Catenation: C ≫ Si > Ge > Sn > Pb
- Maximum covalency: Period 2 elements limited to 4; Period 3 onwards can expand octet
- Acidic strength of hydrides: Increases across a period (CH$$_4$$ < NH$$_3$$ < H$$_2$$O < HF) and down a group (HF < HCl < HBr < HI)
- Thermal stability of hydrides: Decreases down each group
- Oxidising power: F$$_2$$ > Cl$$_2$$ > Br$$_2$$ > I$$_2$$
Tip: For JEE, memorise: (1) structures of XeF$$_2$$, XeF$$_4$$, XeF$$_6$$, XeO$$_3$$, (2) interhalogen shapes (T-shaped, square pyramidal, pentagonal bipyramidal), (3) oxoacids of P, S, and Cl with basicity/strength trends, (4) allotropes of C and P, and (5) properties of HF that make it anomalous.
P-Block Elements Formulas for JEE 2026: Conclusion
The p-Block Elements chapter plays a crucial role in understanding the chemical behavior and reactions of many important elements in the periodic table. Topics such as oxidation states, periodic trends, important compounds, and preparation methods help students build a strong conceptual foundation in inorganic chemistry.
Regular revision of reactions, structures, and trends is essential for mastering this chapter. When students clearly understand these concepts and practice them consistently, it becomes much easier to solve conceptual and reaction-based chemistry questions in competitive exams.
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