Group 13 Elements - Boron Family

Complete guide to Group 13 elements covering boron, aluminum, and their compounds for JEE Main and Advanced

7 min read

Real-Life Connection: From Borax to Borosilicate Glass

Ever wondered why Pyrex glassware doesn’t crack when you move it from freezer to oven? The secret lies in boron - a Group 13 element that makes glass resistant to thermal shock. Borax (used in detergents) and boric acid (antiseptic) are essential boron compounds in daily life. Aluminum, another Group 13 member, is everywhere - from soft drink cans to aircraft bodies!

Group 13 Elements Overview

Members: Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), Thallium (Tl)

Electronic Configuration Pattern

  • General configuration: ns² np¹
  • Boron: [He] 2s² 2p¹
  • Aluminum: [Ne] 3s² 3p¹
  • Gallium: [Ar] 3d¹⁰ 4s² 4p¹

Memory Trick - “BAG IT”: Boron, Aluminum, Gallium, Indium, Thallium

PropertyTrendExplanation
Atomic/Ionic radiusIncreasesAdditional shells added
Ionization energyDecreases (exception: Ga > Al)d-block contraction in Ga
ElectronegativityDecreasesNuclear attraction decreases
Metallic characterIncreasesB is non-metal, rest are metals
Oxidation states+3 common, +1 for TlInert pair effect in Tl

Memory Trick for Ionization Energy: “Gallium Attracts Loosely” - Ga has higher IE than Al due to poor shielding by d-electrons

Boron - The Unique Non-Metal

Why is Boron Different?

  1. Only non-metal in the group
  2. Forms covalent compounds (not ionic)
  3. Electron deficient (only 6 electrons after bonding)
  4. Forms cluster compounds (boranes)

Important Boron Compounds

1. Borax (Na₂B₄O₇·10H₂O)

Natural Sources: Kernite, colemanite, ulexite

Laboratory Preparation:

Na₂B₄O₇ + 7H₂O → Na₂B₄O₇·10H₂O
(heating reverses this)

Key Reactions:

  1. Hydrolysis (gives alkaline solution):
Na₂B₄O₇ + 7H₂O → 2NaOH + 4H₃BO₃
  1. Borax Bead Test (for colored metal ions):
Na₂B₄O₇ --heat--> 2NaBO₂ + B₂O₃
          -Na₂O
B₂O₃ + CoO → Co(BO₂)₂  (blue bead)

Uses:

  • Glass manufacturing (borosilicate glass)
  • Detergents and soaps
  • Antiseptic in cosmetics
  • Flux in metallurgy

2. Boric Acid (H₃BO₃ or B(OH)₃)

Preparation from Borax:

Na₂B₄O₇ + 2HCl + 5H₂O → 2NaCl + 4H₃BO₃

Structure: Layered structure with van der Waals forces between layers (feels soapy)

Acidic Nature (Lewis acid, not Bronsted):

B(OH)₃ + 2H₂O → [B(OH)₄]⁻ + H₃O⁺

Memory Trick: “Boric Accepts Water” - BA₃W → B(OH)₃ accepts OH⁻ from water

Reactions:

  1. Heating:
H₃BO₃ --373K--> HBO₂ --red heat--> B₂O₃
(metaboric acid)  (boric anhydride)
  1. With alcohols (forms volatile esters):
B(OH)₃ + 3CH₃OH → B(OCH₃)₃ + 3H₂O
(gives green flame - test for boric acid)

Boron Hydrides (Boranes)

General Formula: BₙHₙ₊₄ or BₙHₙ₊₆

Important Boranes:

  1. Diborane (B₂H₆) - Most important

Structure:

  • 2 bridging H (3-center-2-electron bonds)
  • 4 terminal H (normal 2-center-2-electron bonds)
  • Banana-shaped bonds

Preparation:

3NaBH₄ + 4BF₃ → 2B₂H₆ + 3NaBF₄

2BF₃ + 6LiH --450K--> B₂H₆ + 6LiF

Key Reactions:

  1. Hydrolysis:
B₂H₆ + 6H₂O → 2B(OH)₃ + 6H₂
  1. With ammonia:
B₂H₆ + 2NH₃ → 2BH₃·NH₃ (at low temp)
3B₂H₆ + 6NH₃ → 3[BH₂(NH₃)₂]⁺[BH₄]⁻ (at high temp)
B₂H₆ + 6NH₃ --heat--> 2B₃N₃H₆ + 12H₂ (borazine)
  1. With oxygen:
B₂H₆ + 3O₂ → B₂O₃ + 3H₂O (highly exothermic - rocket fuel)

Memory Trick: “Big Brother Has Six” - B₂H₆ structure has 2 Bridge bonds and 4 Terminal bonds (2+4=6)

Borazine (B₃N₃H₆) - Inorganic Benzene

Structure: Similar to benzene with alternating B and N atoms

Preparation:

3B₂H₆ + 6NH₃ → 2B₃N₃H₆ + 12H₂

Aluminum - The Versatile Metal

Occurrence and Extraction

Ores:

  • Bauxite (Al₂O₃·2H₂O) - main ore
  • Corundum (Al₂O₃)
  • Cryolite (Na₃AlF₆)

Extraction (Hall-Heroult Process):

  1. Purification (Baeyer’s Process):
Al₂O₃·2H₂O + 2NaOH → 2NaAlO₂ + 3H₂O (at 150°C)
NaAlO₂ + 2H₂O → Al(OH)₃ + NaOH (on dilution)
2Al(OH)₃ --heat--> Al₂O₃ + 3H₂O
  1. Electrolysis:
Cathode: Al³⁺ + 3e⁻ → Al
Anode: C + O²⁻ → CO + 2e⁻
        2C + O²⁻ → CO₂ + 4e⁻

Memory Trick: “BACH” - Bauxite, Alkali treatment, Carbon anode, Hall-Heroult

Properties and Reactions

Amphoteric Nature:

2Al + 6HCl → 2AlCl₃ + 3H₂ (with acids)
2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂ (with bases)

Passivation:

2Al + 3/2 O₂ → Al₂O₃ (protective oxide layer)
Al becomes passive in conc. HNO₃

Thermite Reaction (highly exothermic):

Fe₂O₃ + 2Al → 2Fe + Al₂O₃ (ΔH = -850 kJ)
Used in welding railway tracks

Memory Trick: “TAP” - Thermite (Al reduces), Amphoteric, Passivation

Aluminum Compounds

Aluminum Chloride (AlCl₃)

Preparation:

2Al + 3Cl₂ → 2AlCl₃ (anhydrous)

Structure:

  • Exists as Al₂Cl₆ dimer (coordinate bonds)
  • Lewis acid (electron deficient)

Uses:

  • Friedel-Crafts catalyst
  • Polymerization catalyst

Alums (Double Salts)

General Formula: M₂SO₄·M₂(SO₄)₃·24H₂O

  • M = K, Na, NH₄
  • M’ = Al, Fe, Cr

Example: Potash alum - K₂SO₄·Al₂(SO₄)₃·24H₂O

Uses: Water purification, mordant in dyeing

Diagonal Relationship: Boron and Silicon

PropertySimilarity
Non-metallicBoth are metalloids
Acidic oxidesB₂O₃ and SiO₂
Chlorides hydrolyzeBCl₃ and SiCl₄
Form hydridesBoranes and silanes
GlassesBorosilicate glass

Memory Trick: “BS Pair” - Boron-Silicon show diagonal relationship

Interactive Demo: Visualize Group 13 in the Periodic Table

Explore the position and properties of Group 13 elements (Boron family) in the periodic table.

Common Mistakes to Avoid

  1. Mistake: Writing boric acid as H₃BO₃ donating H⁺

    • Correct: It’s a Lewis acid accepting OH⁻

  2. Mistake: AlCl₃ exists as monomer

    • Correct: Forms Al₂Cl₆ dimer with coordinate bonds

  3. Mistake: All Group 13 show +3 oxidation only

    • Correct: Tl shows +1 due to inert pair effect

  4. Mistake: Diborane has normal 2-center-2-electron bonds only

    • Correct: Has 3-center-2-electron bridge bonds

  5. Mistake: Aluminum dissolves in concentrated HNO₃

    • Correct: Forms protective oxide layer (passivation)

Practice Problems

Level 1: JEE Main Basics

  1. Why does Ga have higher ionization energy than Al despite being below it?

  2. Write the equation for the hydrolysis of borax and explain why the solution is alkaline.

  3. What is the hybridization of B in B₂H₆ for: a) Terminal B-H bonds b) Bridge B-H bonds

  4. Why is AlCl₃ a Lewis acid? Draw its dimeric structure.

Level 2: JEE Main Advanced

  1. When Al₂O₃ is treated with NaOH followed by CO₂, what is the final product?

  2. Calculate the number of 3-center-2-electron bonds in B₄H₁₀.

  3. Explain why boric acid is a weak monobasic acid despite having three OH groups.

  4. Arrange the following in increasing order of Lewis acidity: BCl₃, BBr₃, BF₃

Level 3: JEE Advanced

  1. B₂H₆ reacts with NH₃ in 1:2 ratio at high temperature to form an ionic compound. Write balanced equation and explain the bonding.

  2. A compound X of boron reacts with ammonia at 200°C to give a compound Y (isoelectronic with benzene). Y on heating with water gives back X and ammonia. Identify X and Y with equations.

  3. In the extraction of aluminum, why is cryolite added to bauxite? Calculate the cell potential if the decomposition potential of Al₂O₃ is 2.06 V.

  4. Explain why AlF₃ is high melting solid while AlCl₃ is low melting and sublimes easily. Correlate with their structures.

  • Extraction of Metals - Hall-Heroult process
  • Qualitative Analysis - Borax bead test
  • Environmental Chemistry - Aluminum in water treatment

Memory Palace for Group 13

Imagine a BAG filled with IT items:

  • Bag = Boron (non-metal, makes borax for cleaning the bag)
  • Aluminum foil wrapping items
  • Gadgets made with Gallium (liquid metal thermometers)
  • Ink cartridges with Indium
  • Tape with Thallium compounds

Floor 1: Boron’s lab

  • Borax crystals (Na₂B₄O₇·10H₂O)
  • Boric acid bottles with green flame test
  • Diborane cylinders (highly reactive - handle with care!)

Floor 2: Aluminum factory

  • Bauxite ore pile
  • Electrolytic cell (Hall-Heroult)
  • Thermite welding section (sparks flying!)

Floor 3: Trends tower

  • Elevator going down = increasing atomic radius
  • Stairs going down = decreasing ionization energy
  • Mirror at Ga = ionization energy reflection (higher than Al)

Quick Revision Checklist

  • Electronic configuration: ns² np¹
  • Boron is non-metal, rest are metals
  • Borax formula and hydrolysis equation
  • Boric acid is Lewis acid (not Bronsted)
  • Diborane structure (2 bridge + 4 terminal H)
  • 3-center-2-electron bonds in B₂H₆
  • Borazine = inorganic benzene
  • Hall-Heroult process for Al extraction
  • Aluminum is amphoteric and shows passivation
  • Thermite reaction and its use
  • AlCl₃ exists as Al₂Cl₆ dimer
  • Inert pair effect in Tl
  • Diagonal relationship: B and Si

Important Equations Summary

1. Borax hydrolysis: Na₂B₄O₇ + 7H₂O → 2NaOH + 4H₃BO₃
2. Boric acid test: H₃BO₃ + 3C₂H₅OH → B(OC₂H₅)₃ + 3H₂O (green flame)
3. Diborane preparation: 3NaBH₄ + 4BF₃ → 2B₂H₆ + 3NaBF₄
4. Diborane hydrolysis: B₂H₆ + 6H₂O → 2B(OH)₃ + 6H₂
5. Baeyer's process: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O
6. Thermite: Fe₂O₃ + 2Al → 2Fe + Al₂O₃
7. Al with base: 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

Last updated: July 2025 Next topic: Group 14 Elements - Carbon Family