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JEE Revision: P-Block Elements (Groups 13 to 15) Notes

JEE Revision: P-Block Elements (Groups 13 to 15)

This one-shot lecture covers the fundamental concepts, periodic trends, and chemical reactivity of p-block elements focusing on Groups 13, 14, and 15 for JEE Main. It explains key phenomena such as the inert pair effect, anomalous behavior of second-period elements, catenation, allotropy of carbon, and the trends in trihalides, hydrides, and oxides. The session integrates past-year JEE Main questions to reinforce core principles and exam patterns.

JEE
Chemistry
English · 10 topics
Checked against the video on 23 Oct 2026

Made by AI from the YouTube video P-BLOCK in One Shot: All Concepts & PYQs Covered | JEE Main & Advanced (opens YouTube in a new tab) by JEE Wallah, then checked against it. All credit for the teaching goes to the creator. Tap a topic’s time to confirm a fact in the video.

JEE Revision: P-Block Elements (Groups 13 to 15)

English10 topics · 8 MCQs · 12 flashcardsWatch the video (opens YouTube in a new tab)

Checked against the video

In short

This one-shot lecture covers the fundamental concepts, periodic trends, and chemical reactivity of p-block elements focusing on Groups 13, 14, and 15 for JEE Main. It explains key phenomena such as the inert pair effect, anomalous behavior of second-period elements, catenation, allotropy of carbon, and the trends in trihalides, hydrides, and oxides. The session integrates past-year JEE Main questions to reinforce core principles and exam patterns.

Introduction to P-Block & General Characteristics

P-block elements are those in which the last electron enters the outer p-subshell, covering Groups 13 through 18.
The general outer electronic configuration for p-block elements is ns² np^1-6, excluding helium which has a 1s² configuration.
Must knowThe maximum oxidation state shown by a p-block element equals the total number of valence electrons (or Group number - 10).
Non-metals and metalloids exist exclusively in the p-block of the modern periodic table.
Metallic character increases down the group, while non-metallic character decreases.

The Inert Pair Effect & Oxidation States

Due to the poor shielding effect of intervening inner d and f electrons, outer s electrons experience a stronger nuclear pull.
Must knowThe reluctance of the valence ns² electron pair to participate in chemical bonding is called the inert pair effect.
Because of the inert pair effect, the stability of the lower oxidation state increases down the group, whereas the stability of the higher oxidation state decreases.
In Group 13, the +1 oxidation state becomes increasingly stable down the group, making Tl^+ more stable than Tl³+.
In Group 14, Pb²+ is more stable than Pb⁴+, meaning Pb⁴+ compounds act as powerful oxidising agents.
Lower oxidation state compounds are more ionic than higher oxidation state compounds according to Fajans' rule.

Anomalous Properties of Second-Period Elements

The first element of each group differs from the heavier members due to its small size, high electronegativity, high ionisation enthalpy, and unavailability of d orbitals.
Second-period elements have a maximum covalency restricted to 4, whereas heavier elements can expand their covalence beyond 4 using vacant d orbitals.
Boron forms [BF4]^- with a maximum covalency of 4, while aluminium forms [AlF6]³- expanding its covalency to 6.
Must knowThe first member of each group has a unique ability to form strong pπ-pπ multiple bonds with itself and other small atoms.
Heavier elements form weaker pπ-pπ bonds because their atomic orbitals are too large and diffuse to undergo effective lateral overlap; they form dπ-pπ or dπ-dπ bonds instead.

Group 13 Elements: Properties and Trends

Group 13 consists of boron (B), aluminium (Al), gallium (Ga), indium (In), and thallium (Tl); boron is a typical non-metal while the rest are metals.
Boron forms an extremely hard network solid of B12 icosahedral units (12 corners and 20 faces) with an unusually high melting point.
Must knowThe order of atomic radii in Group 13 contains an anomaly: B < Ga < Al < In < Tl, where Ga is smaller than Al due to poor shielding by 3d electrons.
The ionisation enthalpy trend has anomalies due to d and f electron shielding: B > Tl > Ga > Al > In.
Gallium has an unusually low melting point (303 K) and a very high boiling point (2676 K), making it useful in high-temperature thermometry.
Liquid gallium is denser than solid gallium, showing anomalous density behavior similar to water.

Group 13 Chemical Properties & Reactions

Boron does not form B³+ ions because the sum of its first three ionisation enthalpies is exceedingly high, restricting it to covalent compounds.
In the trivalent state, Group 13 compounds have 6 valence electrons (incomplete octet) and act as Lewis acids.
Must knowThe Lewis acidic strength of boron trihalides follows the order: BF3 < BCl3 < BBr3 < BI3, because back-bonding (2pπ-2pπ) is strongest in BF3 and weakens as halogen size increases.
AlCl3 achieves stability by dimerizing into Al2Cl6 via coordinate bridge bonds.
B2O3 is acidic, Al2O3 and Ga2O3 are amphoteric, and In2O3 and Tl2O3 are basic.
Passivity occurs when metals like Al, Cr, Fe, Co, Ni, and Be are treated with 80% concentrated HNO3 due to the formation of a protective oxide film.

Group 14 Elements: Physical Trends & Oxidation States

Group 14 consists of carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb).
Carbon and silicon are non-metals, germanium is a metalloid, and tin and lead are soft metals.
All Group 14 members exhibit catenation except lead (Pb), with catenation tendency decreasing down the group: C >> Si > Ge ≈ Sn.
Must knowSn²+ acts as a reducing agent because Sn⁴+ is more stable, whereas Pb⁴+ acts as an oxidising agent because Pb²+ is more stable.
To prevent atmospheric oxidation of SnCl2 to SnCl4, a piece of metallic tin is kept in bottles of SnCl2 solution.

Group 14 Reactivity and Halides

Dioxides (MO2) with higher oxidation states (+4) are more acidic than monoxides (MO) with lower oxidation states (+2).
CO is neutral, CO2, SiO2, and GeO2 are acidic, while SnO, SnO2, PbO, and PbO2 are amphoteric.
Must knowCCl4 cannot be hydrolysed by water because carbon lacks vacant d orbitals to accept electron pairs from water.
SiCl4 undergoes complete hydrolysis in water to produce silicic acid, Si(OH)4, and HCl.
[SiF6]²- is stable and known, whereas [SiCl6]²- is not formed due to the steric hindrance of six large chloride ions around silicon.

Allotropes of Carbon

Diamond has a rigid 3D tetrahedral network of sp³ hybridized carbon atoms with a C-C bond length of 154 pm, making it extremely hard and an electrical insulator.
Graphite has a 2D planar layered hexagonal lattice of sp² hybridized carbon atoms with a C-C bond length of 141.5 pm and layer separation of 340 pm held by van der Waals forces.
Graphite conducts electricity due to delocalized π electrons and is used as a dry lubricant at high temperatures.
Must knowBuckminsterfullerene (C60) contains 20 six-membered rings and 12 five-membered rings.
In C60, six-membered rings can fuse with both six- and five-membered rings, but five-membered rings can only fuse with six-membered rings.

Group 15 Elements: General & Physical Trends

Group 15 (pnictogens) includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).
Dinitrogen is a diatomic gas (N2) with a very high bond dissociation energy (941.4 kJ/mol) due to its N≡N triple bond, making it inert at room temperature.
Nitrogen shows an anomalous single bond weakness: the single N-N bond is weaker than the single P-P bond because of high interelectronic repulsions between non-bonding lone pairs on small nitrogen atoms.
Consequently, the catenation tendency of nitrogen is significantly weaker than that of phosphorus.
PCl5 is known, but NCl5 does not exist because nitrogen cannot expand its covalency beyond 4 due to the absence of d orbitals.

Group 15 Hydrides, Halides & Oxides

Must knowThe boiling point order of Group 15 hydrides is: PH3 < AsH3 < NH3 < SbH3 < BiH3; NH3 has an abnormally high boiling point due to intermolecular hydrogen bonding.
The thermal stability and bond dissociation energy of hydrides decrease down the group: NH3 > PH3 > AsH3 > SbH3 > BiH3, which causes reducing character to increase down the group.
The basic strength of hydrides decreases down the group: NH3 > PH3 > AsH3 > SbH3 > BiH3, as lone pair electron density is diluted over larger orbitals.
Nitrogen forms only one stable trihalide: NF3; other trihalides of nitrogen are unstable.
Oxides in higher oxidation states are more acidic: N2O5 is more acidic than N2O3; among nitrogen oxides, N2O and NO are neutral, whereas NO2 is a brown gas with an odd electron.

Key terms

Inert Pair Effect: The reluctance of outer ns² electrons to participate in bonding in heavier p-block elements due to poor shielding of inner d/f electrons.
Catenation: The tendency of an element to link with atoms of the same element through covalent bonds to form chains or rings.
Back-bonding: Side-to-side donation of a lone pair from a filled orbital of an adjacent atom into an empty orbital of a central atom (e.g., in BF3).
Pnictogens: The collective name for Group 15 elements, derived from their suffocating or choking nature.
Amphoteric Oxide: An oxide that reacts with both acids and bases to produce salt and water (e.g., Al2O3, SnO2, PbO).

Exam tips and traps

In Group 13 atomic radii, always remember the inversion: Ga is smaller than Al due to transition contraction (poor shielding by 3d electrons).
In boiling points of Group 15 hydrides, NH3 does not have the highest boiling point overall; SbH3 and BiH3 are higher due to large van der Waals forces.

Quick revision

Read these the night before the exam.

Maximum oxidation state of a p-block element equals its total number of valence electrons.
Atomic radius order in Group 13: B < Ga < Al < In < Tl.
Ionisation enthalpy order in Group 13: B > Tl > Ga > Al > In.
Lewis acid strength order of boron trihalides: BF3 < BCl3 < BBr3 < BI3.
Tin(II) acts as a reducing agent, while Lead(IV) acts as a strong oxidising agent.
CCl4 cannot be hydrolysed because carbon lacks vacant d orbitals.
Buckminsterfullerene (C60) contains exactly 20 six-membered rings and 12 five-membered rings.
In C60, five-membered rings are fused only to six-membered rings.
Single N-N bond is weaker than single P-P bond due to lone pair-lone pair repulsion on small nitrogen atoms.
Boiling point order of Group 15 hydrides: PH3 < AsH3 < NH3 < SbH3 < BiH3.
NF3 is the only stable trihalide of nitrogen.

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