Chapter 1: Group 13 — Boron Family

Group 13 elements (B, Al, Ga, In, Tl) have the outer configuration $ns^{2}$ $np^{1}$ and typically exhibit +3 oxidation states. Boron is anomalous due to its small size and high electronegativity — it forms only covalent, electron-deficient compounds and acts as a Lewis acid.

Diborane ($B_{2}H_{6}$): The key structural feature is two 3-centre-2-electron (3c-2e) banana bonds connecting the two B atoms via two bridging hydrogen atoms. There are also four terminal B-H bonds (normal 2c-2e bonds). Diborane is synthesized by the reaction of $BF_{3}$ with $LiAlH_{4}$ and is hydrolysed by water to give $H_{3}BO_{3}$ and $H_{2}$.

Borax ($Na_{2}B_{4}O_{7}$·10$H_{2}$O): Contains 2 $BO_{3}$ (trigonal) and 2 $BO_{4}$ (tetrahedral) units in its anion. Used in the borax bead test where heated borax dissolves metal oxides to give coloured metaborates.

Boric acid ($H_{3}BO_{3}$): A weak monobasic Lewis acid. Reaction: $H_{3}BO_{3}$ + $H_{2}$O → [B(OH)_{4}]^{-} + $H^{+}$. Forms a layered solid via O-H···O hydrogen bonds.

Aluminium chloride ($AlCl_{3}$): Exists as dimer $Al_{2}Cl_{6}$; electron-deficient Al achieves octet by forming two coordinate Al-Cl bonds. Key Lewis acid catalyst for Friedel-Crafts reactions. The inert pair effect down Group 13 stabilises Tl(+1).

Chapter 2: Group 14 — Carbon Family

Group 14 elements (C, Si, Ge, Sn, Pb) have $ns^{2}$ $np^{2}$ configuration. Carbon's allotropes illustrate how structure determines properties: diamond ($sp^{3}$, insulator, hardest), graphite ($sp^{2}$, conductor, lubricant), and $C_{60}$ ($sp^{2}$, spherical cage).

CO: Neutral ligand coordinating via C; toxic by binding haemoglobin $Fe^{2+}$ ~200× more strongly than $O_{2}$. Mg burns in C$O_{2}$ (2Mg + C$O_{2}$ → 2MgO + C) — critical safety fact.

Silicon compounds: Silicates based on $SiO_{4}^{4-}$ tetrahedra in various linkages; silicones –($R_{2}SiO$)ₙ– are water-repellent polymers; zeolites are 3D aluminosilicates used as molecular sieves and catalysts.

Chapter 3: Group 15 — Nitrogen Family and Industrial Chemistry

Group 15 (N, P, As, Sb, Bi) has $ns^{2}$ $np^{3}$. Nitrogen's N≡N triple bond (945 kJ/mol) makes it inert.

Haber Process: $N_{2}$ + 3$H_{2}$ ⇌ $2NH_{3}$. Finely divided Fe catalyst, 450°C, 200 atm. Compromise between yield (favoured by low T) and rate (favoured by high T). High pressure favours fewer moles of gas product.

Ostwald Process: $NH_{3}$ → NO (Pt/Rh, 500°C) → N$O_{2}$ (room T, no catalyst) → $HNO_{3}$ (absorption in water). NO recycled in Step 3.

Nitrogen Oxides: $N_{2}$O (+1, neutral), NO (+2, neutral, paramagnetic), N_{2}$$O_{3} (+3, acidic, HN$O_{2}$ anhydride), N$O_{2}$ (+4, acidic, paramagnetic, dimerises to N_{2}$$O_{4}), N_{2}$$O_{5} (+5, acidic, $HNO_{3}$ anhydride).

Phosphorus allotropes: White P ($P_{4}$, reactive, toxic), Red P (polymeric, stable), Black P (most stable, layered). $PCl_{5}$: $sp^{3}$d, trigonal bipyramidal; axial bonds longer than equatorial. P oxoacid basicity = P-OH count: H_{3}P$$O_{2} (1) < H_{3}P$$O_{3} (2) < H_{3}P$$O_{4} (3).