p-Block Elements
p-Block Elements
This domain covers Groups 13–18, focusing on periodic trends, important compounds and structure–bonding explanations.
Core rules
- Inert-pair effect: heavier elements show lower oxidation states (Tl⁺, Pb²⁺, Bi³⁺).
- N₂ is inert because of a strong triple bond and no low-energy d orbitals; phosphorus is more reactive.
- Oxoacid strength rises with increasing oxidation state and with more electronegative central atoms: HClO < HClO₂ < HClO₃ < HClO₄.
- H₃PO₃ is diprotic and H₃PO₂ monoprotic because P–H bonds do not ionise.
- Interhalogens XY_n are often more reactive than the halogens; reactivity follows the electronegativity difference.
- Noble gases: XeF₂ linear, XeF₄ square planar, XeF₆ distorted octahedral.
Worked example Arrange HClO, HClO₂, HClO₃, HClO₄ in increasing acid strength and explain. The oxidation states of Cl are +1, +3, +5 and +7. Higher oxidation state increases the positive character of Cl, withdraws electron density from O–H and stabilises the conjugate base through resonance. Hence HClO < HClO₂ < HClO₃ < HClO₄; HClO₄ is the strongest.
Traps
- Assuming all phosphorus oxoacids are triprotic.
- Writing XeF₆ as a regular octahedron; it is distorted.
- Confusing the bleaching action of Cl₂ (oxidation) with that of SO₂ (reduction).