Ch 7 covers p-block elements of Groups 15 to 18 — nitrogen family, oxygen/chalcogens, halogens, and noble gases. Focus on preparation, properties, oxoacids, and important compounds.
Group 15 (N₂: inert triple bond, NH₃: basic pyramidal, HNO₃: strong oxidising acid). Phosphorus: allotropes (white, red, black). Oxoacids of P: H₃PO₃ (dibasic), H₃PO₄ (tribasic). Group 16 (O₂, O₃: allotropes, H₂SO₄: king of chemicals, contact process). Oxoacids of S: H₂SO₃, H₂SO₄, H₂S₂O₈, H₂S₂O₃.
Halogens: most electronegative elements. HX acid strength: HF < HCl < HBr < HI. Oxoacids of Cl: HOCl, HClO₂, HClO₃, HClO₄ (increasing acid strength). Interhalogen compounds: ClF₃, BrF₅. Noble gases: nearly inert, Xe forms compounds (XeF₂: linear, XeF₄: square planar, XeF₆: distorted octahedral).
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Although F is most electronegative, the H−F bond is very strong (568 kJ/mol) due to the small size of F. This strong bond makes it difficult for HF to donate H⁺ in water. Down the group, bond strength decreases (H−I weakest), making HI the strongest acid. So acid strength depends on bond dissociation energy, not electronegativity alone.
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