Group 13 and 14 Elements

• Distinguish the key compounds of boron (borax, boric acid, diborane) and explain their structures and reactions
• Explain why aluminium forms alums and how thermite reaction works
• Compare allotropes of carbon — graphite, diamond, and fullerene — in terms of structure and properties
• Describe the chemistry of silicon: silicones, silicates, and their industrial uses
• Write and balance reactions of CO, CO₂, and SiO₂ and predict their acidic/basic character
• Identify JEE-level traps in oxidation states, hybridisation, and anomalous behaviour of B and C

Level 1 — Foundations

Group 13 — The Boron Family

Boron — Key Compounds

Borax bead test: Heat borax → loses water → fuses to glassy bead of metaboric acid, then B₂O₃. Dissolve metal oxides in this bead; colour identifies the metal.

Boric acid as Lewis acid: H₃BO₃ + H₂O → [B(OH)₄]⁻ + H⁺
It accepts OH⁻ from water (Lewis mechanism), not a Brønsted acid directly.

Diborane structure:

• 12 electrons, 8 bonds needed but only 12 electrons → 3c-2e bonds
• 2 bridging H atoms (Hb), 4 terminal H atoms (Ht)
• B–Hb–B bridges are "banana bonds"
• Each B is sp³ hybridised

Aluminium

Thermite reaction:
Fe₂O₃ + 2Al → Al₂O₃ + 2Fe ΔH = −852 kJ/mol
Used for welding railway tracks.

Alums: M⁺M³⁺(SO₄)₂·12H₂O
Potash alum: KAl(SO₄)₂·12H₂O — used in water purification, dyeing.

Aluminium is amphoteric:
2Al + 6HCl → 2AlCl₃ + 3H₂↑
2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂↑

Group 14 — The Carbon Family

Carbon Allotropes

CO and CO₂

CO is a reducing agent:
Fe₂O₃ + 3CO → 2Fe + 3CO₂

Silicon Compounds

Silica (SiO₂):

• Giant covalent structure (unlike CO₂ which is molecular)
• Each Si bonded to 4 O; each O bridging 2 Si
• Reacts with HF: SiO₂ + 4HF → SiF₄ + 2H₂O (used to etch glass)
• Reacts with NaOH (fused): SiO₂ + 2NaOH → Na₂SiO₃ + H₂O

Silicates: Based on SiO₄⁴⁻ tetrahedra linked in chains, sheets, or 3D networks.

Silicones: Synthetic organosilicon polymers
General unit: (R₂SiO)ₙ
Made by hydrolysis of R₂SiCl₂ followed by condensation polymerisation.
Properties: water-repellent, thermally stable, electrical insulators.

Level 2 — JEE Depth

Anomalous behaviour of Boron (vs Al):

• B is a metalloid; Al is a metal
• B forms only covalent compounds; Al forms ionic + covalent
• B does not react with steam or dilute acids easily; Al does
• B has no d-orbitals → maximum covalency 4 (in [BF₄]⁻); Al can expand octet

Why is BF₃ a Lewis acid despite B–F bond being strong?
B is electron-deficient (only 6e⁻ around B). The empty p-orbital accepts lone pairs. Despite partial back-donation from F (p→p π), BF₃ is still a Lewis acid.
Lewis acid strength: BF₃ > BCl₃ > BBr₃ (back-bonding decreases, so Lewis acidity increases down).

Inert pair effect in Group 14:
Going down (Ge → Sn → Pb), the +2 state becomes more stable because the 6s² pair is reluctant to participate in bonding.
PbO₂ is a stronger oxidising agent than SnO₂.

Graphite vs Diamond — JEE trap:
Graphite is thermodynamically more stable than diamond at room temperature and pressure (ΔG for diamond → graphite is slightly negative), yet diamond persists because the activation energy for conversion is enormous.

Fullerene (C₆₀) — bond lengths:
C–C between two hexagons: 1.40 Å (double bond character)
C–C between hexagon and pentagon: 1.45 Å (single bond character)

SiO₂ vs CO₂ — structural difference (JEE favourite):
CO₂ forms discrete molecules (pπ–pπ bonding between C and O is effective).
SiO₂ forms a network solid (Si cannot form effective pπ–pπ bonds due to large size and diffuse 3p orbitals → forms σ bonds via sp³ hybridisation).

Hybridisation of carbon in key compounds:

Example 1: Identify the product when excess NaOH reacts with Al₂O₃ and write the reaction.

Step 1: Recognise that Al₂O₃ is an amphoteric oxide.
Step 2: With a base (NaOH), it behaves as an acidic oxide.
Step 3: Reaction:
        Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O
        (sodium aluminate)
Step 4: In excess NaOH (aq), the product is [Al(OH)₄]⁻:
        Al₂O₃ + 2NaOH + 3H₂O → 2Na[Al(OH)₄]
Answer: Sodium tetrahydroxoaluminate(III)

Example 2: Calculate the number of 3-centre 2-electron bonds in diborane (B₂H₆).

Step 1: Count total valence electrons:
        2B × 3e⁻ = 6e⁻
        6H × 1e⁻ = 6e⁻
        Total = 12e⁻

Step 2: Structure has:
        - 4 terminal B–H bonds (normal 2c-2e): 4 × 2 = 8e⁻ used
        - 2 bridging B–H–B bonds: 2 × 2 = 4e⁻ used
        Total = 12e⁻ ✓

Step 3: Each B–H–B bridge is a 3-centre 2-electron bond.
Answer: 2 three-centre two-electron (banana) bonds in B₂H₆.

• Q1: Why does boron form only covalent compounds but aluminium forms ionic compounds too?
• Q2: Write the reaction of borax with HCl. What is the product?
• Q3: Which allotrope of carbon is used as a lubricant and why?
• Q4: Give one chemical distinction between SiO₂ and CO₂ with a reaction.
• Stretch: Q5: The Lewis acid strength order of boron trihalides is BF₃ < BCl₃ < BBr₃. Explain using back-bonding concepts and predict whether BI₃ would be a stronger or weaker Lewis acid than BBr₃.

NCERT Chapter 11 link: P-Block Elements (Part I — Groups 13 and 14), NCERT Chemistry Part 1, Class 12

Exam connections: JEE Mains frequently tests borax bead test, diborane structure, allotropes of carbon, and SiO₂ vs CO₂ comparison. JEE Advanced has asked mechanistic questions on Lewis acidity of BX₃ and inert pair effect.

Study strategy: Build a comparison table for each group (B vs Al, C vs Si vs Pb). Draw structures of diborane, diamond, graphite, and fullerene from memory. For reactions, group them: "with water", "with acid", "with base", "with oxidising agent."

• Use the platform-native live simulation or PhET-style tool for this topic.
• Mirror / body / home activity: physically do the concept and photograph or describe for portfolio.
• Voice or text reflection with AI Mentor: explain the concept to a younger student or family member.

• "Explain this concept to a Class 6 student using one real example from an Indian home, school, market, or festival."
• "What is one common mistake students make here, and how would you catch yourself making it?"
• Stretch: "How does this connect to coding, robotics, money, health, environment, or a future career?"

• Complete the core practice + one extension activity (photo, table, short reflection, or mini-project) for base XP + topic badge.
• 5-7 day streak or family discussion note = multiplier + visible artifact in parent/principal dashboard.
• Best real-world application stories (anonymised) featured on class or national leaderboard.

• One hands-on project or measurement using the Drishti kit or household items that makes the concept physical.
• Direct link to at least one Future Skill track (Money Management, Green Tech, Cyber Defenders, Micro-Entrepreneurship, AI Mastery, Sustainable Living, Personality Development).
• Coding extension where relevant (simple script, simulation, or data logging).

This material emphasises experiential "learning by doing", competency (apply/create/analyse), vocational exposure, critical thinking, and multidisciplinary connections. Designed to feed live worlds, AI Mentor (with memory), gamification, robotics, parent analytics, and future skills — not just exam prep.

Portfolio Evidence Idea: Your photo/table/reflection/project + one sentence on "How this helps me in real life or a possible future path."

Open the Practice tab for aligned questions (easy/medium/hard + case-based) with full AI scaffolding.

See curriculum for cross-links and the full future-skills/robotics chapters.