Chapter 3: Group III-A and Group IV-A Elements

Includes Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), Thallium (Tl).

• General Characteristics: ns²np¹ configuration. Boron is non-metal, others are metals. Metallic character increases down the group.
• Peculiar Behaviour of Boron: Non-metal, small size, high ionization energy. Forms only covalent compounds (e.g., BCl3). Does not form stable cations.

Borax (Na2B4O7.10H2O)

• Occurrence: Tincal, Colemanite.
• Preparation: From Colemanite (Ca2B6O11) reacting with Na2CO3.
• Bead Test: Forms glassy bead (NaBO2 + B2O3) which reacts with metal oxides to give colored beads (e.g., Co gives Blue, Cu gives Green/Red). Used for qualitative analysis.
• Uses: Water softening, soldering flux, heat resistant glass (Pyrex).

Boric Acid (H3BO3)

• Properties: White crystalline solid, soluble in hot water. Weak monobasic acid (accepts OH⁻).
• Uses: Antiseptic (eye wash), pottery glazes, candle wicks.

• Reactions: Reacts with O2 to form protective Al2O3 layer. Amphoteric nature (dissolves in both acids and alkalis). Reacts with N2 to form AlN. Thermite reaction with Fe2O3 used in welding.
• Uses: Light weight alloys, transmission cables, cooking utensils, foils.

Includes Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), Lead (Pb).

• General Characteristics: ns²np² configuration. C, Si (Non-metals), Ge (Metalloid), Sn, Pb (Metals).
• Inert Pair Effect: Reluctance of s-electrons to participate in bonding. Prominent in heavier elements (Pb). Stability of +2 oxidation state increases down the group (Pb²⁺ > Pb⁴⁺).

Oxides

• CO: Neutral, toxic, reducing agent. Triple bond (one coordinate covalent).
• CO2: Acidic (forms H2CO3), linear, non-polar.
• SiO2 (Silica): Giant covalent network solid. Tetrahedral assembly. Hard, high MP.

Silicones

Polymers with alternating Si-O backbone and organic side groups (R2SiO)n. High thermal stability, water repellent. Used as lubricants, sealants, insulators.

Elements (Si, Ge) having conductivity between conductors and insulators. Conductivity increases with temperature.

• Litharge (PbO): Yellow/Reddish yellow. Used in paints, flint glass.
• Red Lead (Pb3O4): Scarlet powder. Used in anti-corrosion paints, storage batteries.
• White Lead (2PbCO3.Pb(OH)2): Basic lead carbonate. White pigment, good covering power. Darkens with H2S.
• Chrome Yellow (PbCrO4): Yellow pigment.