Bismuth (Bi) - Comprehensive Study Guide for JEE/NEET & CBSE

Introduction: Why Bismuth Matters

Bismuth (Bi) is a post-transition metal, historically grouped with the nitrogen family (Group 15). It is the heaviest stable member of this group, exhibiting distinct metallic properties and chemistry influenced by the inert pair effect. Its low toxicity, unique physical properties, and diverse chemical applications make it significant in various industrial and pharmaceutical sectors, offering a safer alternative to lead in many uses.

CBSE/JEE Quick Revision Notes

• Symbol: Bi
• Atomic Number: 83
• Atomic Mass: 208.98 u
• Group: 15 (Nitrogen Family, Pnictogens)
• Period: 6
• Block: p-block
• Nature: Metal
• Electronic Configuration:
  • Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p³
  • Condensed: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³
• Common Oxidation States: +3, +5 (due to inert pair effect, +3 is more stable)
• Valency: 3, 5
• Density (at 20°C): 9.78 g/cm³
• Melting Point: 271.4°C
• Boiling Point: 1564°C
• Electronegativity (Pauling): 2.02
• Ionization Energy (1st): 703 kJ/mol
• Key Characteristic: Only naturally occurring element with an atomic number greater than 82 that is not radioactive (though often considered the heaviest stable element, it is actually slightly radioactive with an extremely long half-life of 1.9 x 10¹⁹ years for alpha decay to Thallium-205, which is practically stable for all chemical purposes).

Electron Configuration & Bonding Behavior

Bismuth’s electronic configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³ reveals five valence electrons (6s² 6p³).

• Oxidation States:
  • +3 Oxidation State: This is the most stable and common oxidation state for Bismuth. It arises from the participation of the three 6p electrons in bonding, while the two 6s electrons remain unshared due to the inert pair effect. This effect becomes prominent for heavier elements in p-block, where the s-electrons are less available for bonding due to poor shielding by f and d electrons, leading to higher nuclear charge experienced by s-electrons.
  • +5 Oxidation State: This state requires the involvement of all five valence electrons (6s² and 6p³). It is less stable than the +3 state and acts as a strong oxidizing agent (e.g., in NaBiO₃). This is because Bismuth in the +5 state readily accepts electrons to achieve the more stable +3 state.
• Bonding: Bismuth typically forms covalent compounds, especially with more electronegative elements like halogens (e.g., BiCl₃). However, in compounds with highly electronegative elements or with large counterions, it can also exhibit ionic character (e.g., in BiF₃). Its compounds are often polymeric in structure.

Crucial Chemical Reactions

Bismuth’s chemical behavior is characterized by its preference for the +3 oxidation state.

1. Reaction with Air/Oxygen

Bismuth is stable in dry air at room temperature but burns in oxygen when heated to form bismuth(III) oxide.

• 4Bi(s) + 3O₂(g) → 2Bi₂O₃(s) (Bismuth(III) oxide)

2. Reaction with Halogens

Bismuth reacts directly with halogens to form trihalides (BiX₃), where X = F, Cl, Br, I. The pentahalides (BiX₅) are less stable and generally only formed with fluorine (BiF₅).

• 2Bi(s) + 3F₂(g) → 2BiF₃(s) (Bismuth(III) fluoride)
• 2Bi(s) + 3Cl₂(g) → 2BiCl₃(s) (Bismuth(III) chloride)
• BiF₃(s) + F₂(g) → BiF₅(s) (Bismuth(V) fluoride - strong oxidizing agent)

3. Reaction with Acids

Bismuth does not react with non-oxidizing acids (like dilute HCl, H₂SO₄). It reacts with oxidizing acids.

• With Concentrated Nitric Acid: Bi(s) + 4HNO₃(conc) → Bi(NO₃)₃(aq) + NO(g) + 2H₂O(l) Note: The actual product is often dinitrogen tetroxide (NO₂) due to further oxidation of NO. Bi(s) + 6HNO₃(conc) → Bi(NO₃)₃(aq) + 3NO₂(g) + 3H₂O(l)

• With Concentrated Sulfuric Acid (Hot): 2Bi(s) + 6H₂SO₄(conc, hot) → Bi₂(SO₄)₃(aq) + 3SO₂(g) + 6H₂O(l)

4. Hydrolysis of Bismuth(III) Salts

Bismuth(III) salts, especially halides, undergo hydrolysis in water to form insoluble bismuthyl (BiO⁺) compounds or hydroxides, indicating the basic nature of Bi(OH)₃.

• BiCl₃(aq) + H₂O(l) ⇌ BiOCl(s) + 2HCl(aq) (Bismuthyl chloride or Bismuth oxychloride)
• Bi(NO₃)₃(aq) + 3H₂O(l) ⇌ Bi(OH)₃(s) + 3HNO₃(aq)

5. Formation of Bismuthates

Strong oxidizing agents can oxidize bismuth(III) compounds to bismuthates(V), containing the BiO₃⁻ ion, where Bismuth is in the +5 oxidation state.

• NaBiO₃ (Sodium bismuthate) is a powerful oxidizing agent. 2MnSO₄(aq) + 5NaBiO₃(s) + 14H⁺(aq) → 2MnO₄⁻(aq) + 5Bi³⁺(aq) + 5Na⁺(aq) + 7H₂O(l)

Industrial and Biological Importance

Industrial Importance

1. Alloys: Bismuth forms alloys with exceptionally low melting points, making them useful in safety devices, fire sprinklers, and fusible plugs.
   • Wood’s metal: An alloy of Bi, Pb, Sn, and Cd, with a melting point of ~70°C.
   • Rose’s metal: An alloy of Bi, Pb, and Sn, with a melting point of ~98°C.
   • Bismuth-containing alloys are increasingly used as non-toxic alternatives to lead-based solders and plumbing materials.
2. Cosmetics: Bismuth oxychloride (BiOCl) is used as a pearlescent pigment in cosmetics like eyeshadows, nail polishes, and foundations due to its metallic luster and shimmer.
3. Catalysis: Bismuth molybdate is used as a catalyst in the production of acrylonitrile.
4. Magnetism: Bismuth is the most diamagnetic of all metals, and its alloys can exhibit unique magnetic properties.
5. Thermoelectric Materials: Bismuth telluride (Bi₂Te₃) and its alloys are important thermoelectric materials, converting heat into electricity and vice versa.

Biological Importance

1. Pharmaceuticals: Bismuth compounds have medicinal applications, primarily for gastrointestinal issues.
   • Bismuth subsalicylate: The active ingredient in “Pepto-Bismol,” used to treat indigestion, nausea, and diarrhea. It acts as an antacid, mild antibiotic, and anti-inflammatory agent.
   • Bismuth subgallate: Used in deodorants and as a wound dressing.
   • Antibacterial agents: Some bismuth compounds show activity against Helicobacter pylori, the bacterium responsible for peptic ulcers.
2. Low Toxicity: Compared to other heavy metals (like lead and mercury), bismuth and its compounds exhibit relatively low toxicity. This makes it a preferred substitute in many applications where lead historically dominated.