p - block

(a) Amphoteric Behaviour of p-Block Elements

• Aluminium:

  • Acts as both an acid and a base.

  • Reacts with acids:

  • Reacts with bases:

• Lead:

  • Shows amphoteric properties in oxidation state +2.

  • Reacts with acids:

  • Reacts with bases:

(b) Increasing Stability of Inert Pair Cations

• Stability of lower oxidation states (+1, +2) increases down Groups 3, 4, and 5 due to the inert pair effect.

• Group 3: Tl⁺ is more stable than Tl³⁺.

• Group 4: Pb²⁺ is more stable than Pb⁴⁺.

• Group 5: Bi³⁺ is more stable than Bi⁵⁺.

(c) Octet Rule Exceptions in Groups 3, 5, 6, and 7

• Group 3 (Electron Deficiency): Elements like B and Al form compounds (e.g., BF₃, AlCl₃) with fewer than 8 valence electrons.

• Groups 5-7 (Expanded Octet): Elements like P, S, and Cl form compounds (e.g., PF₅, SF₆, ClF₃) where d-orbitals participate, allowing more than 8 valence electrons.

(d) Structure and Bonding in Al₂Cl₆ and NH₃.BF₃

• Al₂Cl₆: Dimeric structure with Al forming coordinate bonds to Cl atoms, bridging two AlCl3 units.

• NH₃.BF₃: A donor-acceptor complex where NH₃ donates a lone pair to electron-deficient BF3.

(e) Boron Nitride (BN) Structures

• Hexagonal BN: Graphite-like, layered, used as a lubricant.

• Cubic BN: Diamond-like, hard, used in abrasives.

(f) Stability of Oxidation States in Group 4

• CO as a Reducing Agent: Reduces metal oxides (e.g., SnO₂, PbO₂) to lower oxidation states.

• PbO₂ as an Oxidising Agent:

(g) Properties of CO₂ and PbO

• CO₂: Molecular, acidic, reacts with bases.

• PbO: Ionic, amphoteric, reacts with both acids and bases.

(h) Bonding Trends in Group 4 Chlorides

• CCl₄, SiCl₄: Covalent, hydrolysed by water.

• PbCl₂: Ionic, less hydrolysed.

(i) Reactions of Pb²⁺ (aq) with NaOH, Cl^-, and I^-

• NaOH: White Pb(OH)₂, dissolves in excess.

Pb²⁺ + 2NaOH —> Pb(OH)₂ + 2Na

• Cl^-: White PbCl₂ precipitate.

  Pb²⁺ + 2Cl^- —> PbCl₂ - White PPT

• I^-: Yellow PbI₂ precipitate.

  Pb²⁺ + 2I^- —> PbI₂ - Yellow PPT

(j) Reactions of Cl₂ with NaOH

• Cold NaOH: Forms ClO^- and Cl^-.

  Cl₂ + 2NaOH —> NaClO + NaCl + H₂O

• Hot NaOH: Forms ClO₃^-.

  2Cl₂ + 6NaOH —> 5NaCl + NaClO₃ + 3H₂O

(k) Bleaching and Bactericidal Action of Cl² and ClO^-

• Oxidising power disrupts cell structures and organic molecules, making them effective disinfectants.

(l) Reactions of NaCl, NaBr, and NaI with H₂SO₄

• NaCl: Produces HCl.

  NaCl + H₂SO₄ —> NaHSO₄ + HCl

• NaBr: Produces HBr, oxidised to Br₂.

  NaBr + H₂SO₄ —> NaHSO₄ + HBr

  Then

  H₂SO₄  +  2H⁺  +  2Br^-  —>  Br₂  +   SO₂  +  2H₂O

• NaI: Produces HI, oxidised to I₂.

  2Nal + H₂SO₄ —> NaHSO₄ + 2HI

  Then