The P-Block Mindset
P-Block covers Groups 13–18 (IIIA to 0/VIII). Every single anomalous property of the first element in each group (B, C, N, O, F, Ne) follows from one fact: smaller size + higher charge density + no d-orbitals. Understand this and you'll predict anomalies instead of memorizing them.
Group-by-Group Highlights
Boron is a metalloid; others are metals. Boron trifluoride (BF₃) is a Lewis acid — its empty p-orbital accepts electrons. Aluminium shows +3 oxidation state; anomalous catenation in boron. Borax (Na₂B₄O₇·10H₂O) is the most important compound.
Carbon's unique catenation ability leads to allotropes (diamond, graphite, fullerene). Diamond = hardest natural substance (sp³). Graphite = good conductor, used as lubricant (sp²). CO₂ is a gas; SiO₂ is a hard solid (giant covalent). Inert pair effect increases down the group.
N≡N triple bond (bond energy 945 kJ/mol — highest for any diatomic). N has no d-orbitals so maximum covalency is 4. PCl₅ exists but NCl₅ doesn't. Oxoacids of N: HNO₂ (nitrous) and HNO₃ (nitric). Phosphorus allotropes: white (toxic), red, black.
O shows −2 oxidation state normally; F forces it to be +2 in OF₂. Anomalous: H₂O has higher bp than H₂S due to H-bonding. Sulphur allotropes: rhombic (stable below 96°C), monoclinic. Ozone (O₃) — 117.5° bond angle, decomposes to O₂, acts as oxidising agent.
F is the most electronegative element. F₂ is the strongest oxidizing agent. HF has highest bp among HX due to H-bonding. Interhalogen compounds (ICl, BrF₃, IF₇ etc.) are more reactive than parent halogens. Bleaching powder: Ca(OCl)Cl.
Xenon forms compounds (XeF₂, XeF₄, XeF₆, XeO₃). Shapes: XeF₂ = linear, XeF₄ = square planar, XeF₆ = distorted octahedral. All based on VSEPR — a guaranteed question type.
Top 5 NEET P-Block Facts
- Bond angle order: NH₃ (107°) > PH₃ (93.5°) — lone pair repulsion difference
- BeCl₂ is a Lewis acid (incomplete octet), BCl₃ is also Lewis acid (empty orbital)
- Reducing power of hydrides: HF < HCl < HBr < HI (bond strength decreases)
- Acidic strength of oxoacids: increases with oxidation state of central atom
- Nitrogen has no d-orbitals → maximum covalency = 4, not 6 like P
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