Learning Objectives
- Study general introduction to p-block elements (Groups 13 and 14)
- Learn about Boron family (Group 13) and Carbon family (Group 14)
- Understand important compounds and their properties
- Study allotropy and unique properties of boron and carbon
- Know industrial applications of these elements and compounds
Key Concepts
Group 13 (Boron Family): B, Al, Ga, In, Tl
Electronic configuration: ns²np¹. Common oxidation state: +3. Tl also shows +1 (inert pair effect).
Boron: Non-metal/metalloid. Electron deficient (incomplete octet in BX₃). Forms multicentre bonds (e.g., B₂H₆ has 3-centre 2-electron bonds).
Aluminium: Most abundant metal in Earth's crust. Amphoteric oxide and hydroxide.
Inert pair effect: Reluctance of ns² electrons to participate in bonding. Increases down the group. Explains +1 state of Tl.
Important Compounds of Boron
Borax (Na₂B₄O₇·10H₂O): Used as flux, detergent. In water: Na₂B₄O₇ + 7H₂O → 2NaOH + 4H₃BO₃. Borax bead test: gives coloured beads with metal oxides.
Orthoboric acid (H₃BO₃): Weak monobasic Lewis acid (accepts OH⁻). Layered structure with hydrogen bonding.
Diborane (B₂H₆): Electron-deficient compound. Has banana bonds (3c-2e bonds). Burns in air: B₂H₆ + 3O₂ → B₂O₃ + 3H₂O.
Important Compounds of Aluminium
Al₂O₃ (Alumina): Amphoteric oxide. Corundum form is very hard (9 on Mohs scale). With Cr₂O₃: ruby. With Fe/Ti oxides: sapphire.
AlCl₃: Covalent, exists as dimer Al₂Cl₆. Lewis acid, used in Friedel-Crafts reactions.
Group 14 (Carbon Family): C, Si, Ge, Sn, Pb
Electronic configuration: ns²np². Common oxidation states: +4 and +2 (inert pair effect makes +2 stable for Sn, Pb).
Carbon: Shows catenation (ability to form long chains) due to strong C-C bonds. Allotropes: diamond (sp³, hardest), graphite (sp², conductor, lubricant), fullerene (C₆₀, spherical).
Silicon: Second most abundant element. Forms silicates and silicones. No catenation (weak Si-Si bonds).
Important Compounds of Carbon
CO (Carbon monoxide): Toxic, colourless, odourless. Reducing agent. Burns: 2CO + O₂ → 2CO₂. Forms carbonyls with metals (e.g., Ni(CO)₄).
CO₂ (Carbon dioxide): Linear molecule. Acidic oxide: CO₂ + H₂O → H₂CO₃. Greenhouse gas. Solid CO₂ = dry ice.
Important Compounds of Silicon
SiO₂ (Silica): 3D network solid. Very hard. Used in glass, cement. Acidic oxide (reacts with NaOH).
Silicones: Organosilicon polymers (-R₂SiO-)ₙ. Water repellent, heat resistant. Used as lubricants, sealants.
Zeolites: Aluminosilicates with cage-like structures. Used as molecular sieves and catalysts.
Summary
Group 13 elements show +3 oxidation state with increasing +1 tendency down the group (inert pair effect). Boron is electron-deficient and forms multicentre bonds. Group 14 shows +4 and +2 states, with carbon being unique due to catenation and allotropy. Silicon forms extensive silicate structures. Important compounds include borax, diborane, CO, CO₂, and silicones.
Important Terms
- Inert Pair Effect: Reluctance of ns² electrons to bond in heavier elements
- Catenation: Ability of an element to form bonds with itself (chains/rings)
- Allotropy: Existence of an element in different physical forms
- Electron Deficiency: Having fewer electrons than needed for normal bonding
- Banana Bond: 3-centre 2-electron bond in diborane
- Silicones: Organosilicon polymers with Si-O-Si backbone
Quick Revision
- Group 13: ns²np¹; +3 state; Tl shows +1 (inert pair effect)
- Group 14: ns²np²; +4, +2; Carbon: catenation, allotropy
- B₂H₆: 3c-2e bonds; BF₃: Lewis acid (electron deficient)
- Al₂O₃: amphoteric; AlCl₃: Lewis acid, Friedel-Crafts catalyst
- CO: reducing agent, toxic; CO₂: greenhouse gas, acidic oxide
- Diamond (sp³, hard), Graphite (sp², conductor), Fullerene (C₆₀)