p-Block Elements
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Direct answer
The p-block spans Groups 13 to 18, and JEE tests it almost entirely as NCERT facts: structures and reactions of common compounds, plus the periodic logic organising them — the inert pair effect, oxidation state stability, and acid-base or bond-strength trends. The efficient strategy is one page per group: preparations, key reactions, and the explanations JEE reuses every year.
What you must remember
- Group 13: diborane B2H6 is held by three-centre two-electron "banana" bonds; boric acid H3BO3 is a weak monobasic Lewis acid that accepts OH-; borax Na2B4O7·10H2O gives the borax bead; Al2O3 and Al(OH)3 are amphoteric.
- Group 14: carbon's catenation and multiple bonding outdo silicon's; CO reduces Fe2O3 in the blast furnace; silicates are SiO4^4- networks, zeolites aluminosilicate catalysts, silicones Si-O backbone polymers.
- Group 15: N2 is inert from its triple bond; NH3 comes from the Haber process (iron catalyst, high pressure, about 700 K); brown NO2 dimerises to N2O4; HNO3 (Ostwald process) oxidises copper — dilute gives NO, concentrated NO2; solid PCl5 exists as [PCl4]+[PCl6]-.
- Group 16: H2SO4 comes from the Contact process over V2O5; SO2 bleaches by reduction (temporary) against chlorine's permanent oxidative bleaching; ozone forms by silent electric discharge and is a strong oxidant.
- Group 17: oxidising power F2 > Cl2 > Br2 > I2; HF is weak (strong H-F bond); acidity runs HF < HCl < HBr < HI; bleaching powder is Ca(OCl)Cl.
- Group 18: XeF2 linear, XeF4 square planar, XeF6 distorted octahedral, XeO3 pyramidal; XeF6 hydrolyses stepwise to XeO3.
- Inert pair effect: the ns2 pair resists bonding down a group, so Tl+ over Tl3+ and Pb2+ over Pb4+ dominate among the heavier elements.
- Hydride trends: acidity rises down a group (NH3 < PH3, H2O < H2S) while bond angle falls (NH3 107°, PH3 much smaller).
Common confusion
The commonest error is ignoring the inert pair effect: students expect Tl3+ and Pb4+ to dominate because the group number suggests it, but the reverse holds. Second is bleach chemistry — SO2 bleaches by temporary reduction, chlorine by permanent oxidation; they are not interchangeable. Students also rank acid strength by electronegativity alone: HF is the weakest hydrogen halide because its short strong H-F bond resists ionisation, and hydride stability falls down a group.
Exam-focused takeaway
JEE Main draws p-block questions nearly verbatim from NCERT statements — structures (PCl5, diborane, xenon fluorides), preparations (Haber, Contact, Ostwald) and one-line trend reasons. JEE Advanced blends a compound into reaction sequences or asks structured reasoning — why NO2 dimerises, why boric acid needs water, why XeF6 hydrolyses. Read NCERT line by line here; in no other chapter is the textbook so close to the paper — and use the latest edition, since p-block content is periodically trimmed.
Frequently asked questions
What is the inert pair effect?
Reluctance of the outer s pair to bond in heavy p-block elements, making lower oxidation states (Tl+, Pb2+, Bi3+) more stable down the group.
Why is HF weak while HI is the strongest hydrogen halide?
The H-F bond is short and strong, so it ionises reluctantly; bond strength, not electronegativity, rules this series.
Why does NO2 dimerise?
Nitrogen carries an unpaired electron; pairing two molecules into colourless N2O4 is favourable, so brown pales on cooling.
What shapes do xenon fluorides adopt?
XeF2 linear, XeF4 square planar, XeF6 distorted octahedral — from VSEPR counting of bond pairs and lone pairs.
Why is boric acid called a Lewis acid?
It releases no proton; boron's empty orbital accepts a lone pair from water's OH-, making it effectively monobasic.
How do the bleaching actions of SO2 and Cl2 differ?
SO2 bleaches by reduction and colour returns on standing; chlorine bleaches by oxidation, permanently.