Notes Class 10 Science Chapter 4 Carbon and its Compounds

Notes For All Chapters Science Class 10 CBSE

1. Introduction

Carbon is one of the most important elements in our daily life.

Found in food, clothing, medicines, fuels, books, living organisms.

Abundance in nature:

• Earth’s crust → 0.02% (carbonates, hydrogen-carbonates, coal, petroleum).
• Atmosphere → 0.03% (CO₂).

Despite small amount, it forms millions of compounds.

Reason → tetravalency + catenation.

2. Bonding in Carbon – Covalent Bond

Why not ionic bonds?

Carbon atomic number = 6 → configuration = 2,4.

Needs 4 electrons to complete octet.

• Gaining 4 → C⁴⁻ (unstable, hard for nucleus to hold 10 electrons).
• Losing 4 → C⁴⁺ (requires huge energy).

Hence → Carbon shares electrons → covalent bonding.

Properties of Covalent Compounds

Low melting & boiling points (weak intermolecular forces).

Generally poor conductors of electricity (no ions).

Exist as gases, liquids, or solids.

Examples of Covalent Bond Formation

1. Hydrogen (H₂) → single covalent bond.
2. Chlorine (Cl₂) → single covalent bond.
3. Oxygen (O₂) → double covalent bond.
4. Nitrogen (N₂) → triple covalent bond.
5. Water (H₂O) → O forms 2 single bonds with H.
6. Ammonia (NH₃) → N forms 3 single bonds with H.
7. Methane (CH₄) → Carbon bonds with 4 H atoms.

3. Allotropes of Carbon

Allotropes = different physical forms of same element.

Diamond

• Each C bonded to 4 others → rigid 3D structure.
• Hardest natural substance.
• Non-conductor of electricity.

Graphite

• Each C bonded to 3 others → hexagonal layers.
• Soft, slippery.
• Conducts electricity (free electrons between layers).

Fullerene (C-60)

• Football-shaped molecule.
• Named after Buckminster Fuller (architect).

4. Versatile Nature of Carbon

1. Catenation

• Ability to form long chains, branched chains, and rings.
• Types:
  • Straight chain (C—C—C).
  • Branched chain.
  • Ring/cyclic (cyclohexane, benzene).
• Bonds: Single, double, or triple.
• Unique property → gives rise to millions of compounds.

2. Tetravalency

• Carbon forms 4 covalent bonds with other atoms.
• Bonds with H, O, N, S, Cl, etc.
• Bonds are strong & stable due to small atomic size.

Organic Compounds

• All carbon compounds except carbides, oxides of carbon, carbonates, bicarbonates.
• Earlier → thought to require “vital force” (living origin).
• Friedrich Wöhler disproved → prepared urea from ammonium cyanate (1828).

4.1 Saturated vs Unsaturated Compounds

Saturated hydrocarbons (alkanes): only single bonds.

• Eg: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈).

Unsaturated hydrocarbons: double/triple bonds.

• Eg: Ethene (C₂H₄ → double bond), Ethyne (C₂H₂ → triple bond).

Unsaturated compounds → more reactive.

4.2 Chains, Branches, Rings

Examples of saturated hydrocarbons:

• CH₄, C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄.

Isomerism: Same molecular formula, different structures.

• Example: Butane (C₄H₁₀) → straight chain & branched chain isomers.

Cyclic compounds: carbon atoms in ring.

• Eg: Cyclohexane (C₆H₁₂).
• Benzene (C₆H₆) → cyclic with alternating double bonds.

4.3 Functional Groups

• Replace H atoms in hydrocarbons.
• Give special properties.

4.4 Homologous Series

Family of compounds with:

• Same functional group.
• Differ by –CH₂– unit.
• Same general formula.

Properties:

• Chemical properties → same.
• Physical properties → gradual change (melting/boiling point ↑ with molecular mass).

4.5 Nomenclature (IUPAC)

Identify parent chain (number of carbons).

Add prefix/suffix depending on functional group.

Unsaturated compounds → replace –ane with –ene / –yne.

Examples:

• C₂H₅OH → Ethanol.
• CH₃CHO → Ethanal.
• CH₃COOH → Ethanoic acid.
• CH₃CH₂Cl → Chloroethane.
• C₃H₆ → Propene.
• C₃H₄ → Propyne.

5. Chemical Properties of Carbon Compounds

1. Combustion

• Carbon + O₂ → CO₂ + heat + light.
• CH₄ + O₂ → CO₂ + H₂O + heat + light.
• Ethanol + O₂ → CO₂ + H₂O + heat + light.
• Saturated hydrocarbons → clean flame.
• Unsaturated hydrocarbons → yellow sooty flame.

2. Oxidation

• Alcohols → oxidised to acids by alkaline KMnO₄ / acidified K₂Cr₂O₇.
• Oxidising agents = substances adding oxygen.

3. Addition Reaction

• Unsaturated hydrocarbons + H₂ → saturated hydrocarbon (with Ni/Pd catalyst).
• Example: Hydrogenation of vegetable oils.

4. Substitution Reaction

• In saturated hydrocarbons.
• H replaced by Cl in sunlight.
• CH₄ + Cl₂ → CH₃Cl + HCl.

6. Important Carbon Compounds

(A) Ethanol (C₂H₅OH)

Properties:

• Liquid, soluble in water, active ingredient in alcohol drinks.
• Used as solvent (medicines, tincture iodine).
• Absolute alcohol is poisonous.

Reactions:

• With Na → sodium ethoxide + H₂.
• With conc. H₂SO₄ (443 K) → dehydration to ethene.

Denatured alcohol: Ethanol made unfit for drinking (add methanol + dyes).

(B) Ethanoic Acid (CH₃COOH)

Properties:

• Common name: acetic acid.
• 5–8% solution = vinegar.
• Freezes in winter → glacial acetic acid.

Reactions:

1. Esterification: CH₃COOH + C₂H₅OH → ester (fruity smell) + H₂O.
   1. Reversible, in presence of conc. H₂SO₄.
2. With base: CH₃COOH + NaOH → CH₃COONa + H₂O.
3. With carbonate: CH₃COOH + Na₂CO₃ → CH₃COONa + CO₂ + H₂O.
4. With bicarbonate: CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O.

7. Soaps and Detergents

Soaps

• Sodium/potassium salts of long-chain carboxylic acids.
• Action:
  • Hydrophobic tail → attaches to oil/dirt.
  • Hydrophilic head → dissolves in water.
  • Form micelles → emulsify dirt, washed away.
• Limitation:
  • In hard water → form scum with Ca²⁺, Mg²⁺ ions.

Detergents

• Sodium salts of sulphonic acids / ammonium salts.
• Work in hard water (no scum).
• Used in washing powders, shampoos.