Class 10 Science Notes — Chapter 4: Carbon and its Compounds
Covalent bonding, catenation, hydrocarbons, functional groups, and important organic compounds.
Detailed NCERT notes
- Carbon has 4 valence electrons — forms covalent bonds by sharing.
- Tetravalency + catenation (self-linking) + ability to bond with H, O, N, S, Cl → enormous variety of compounds.
- Allotropes of carbon: diamond (tetrahedral, hard, non-conductor), graphite (hexagonal layers, conducts, lubricant), fullerene C₆₀.
- Hydrocarbons: compounds of C and H only.
- Saturated (alkanes CₙH₂ₙ₊₂): only single bonds, less reactive.
- Unsaturated: alkenes CₙH₂ₙ (double bond), alkynes CₙH₂ₙ₋₂ (triple bond); more reactive.
- Isomers: same molecular formula, different structural formula (from C₄ onward; e.g., n-butane vs isobutane).
- Homologous series: family of compounds with same general formula, same functional group, successive members differ by −CH₂− (mass 14).
- Functional groups (name suffix / prefix): halo (−X), alcohol (−OH), aldehyde (−CHO), ketone (>C=O), carboxylic acid (−COOH).
- IUPAC naming: root (C count: meth, eth, prop, but, pent...) + suffix (−ane, −ene, −yne) + functional group modifier.
- Combustion: all hydrocarbons burn in air. Saturated → clean blue flame; unsaturated → sooty yellow flame (incomplete combustion).
- Oxidation: alcohols → carboxylic acids (using acidified KMnO₄ or alkaline K₂Cr₂O₇, which act as oxidising agents).
- Addition reactions: alkenes/alkynes + H₂ (Ni catalyst) → alkanes; used to hydrogenate vegetable oils into vanaspati.
- Substitution reactions: alkane + Cl₂ (sunlight) → chloroalkane + HCl.
- Ethanol C₂H₅OH: colourless liquid, used as solvent, in beverages; with sodium → sodium ethoxide + H₂; on heating with conc. H₂SO₄ at 443 K → ethene (dehydration).
- Ethanoic acid CH₃COOH (glacial): m.p. 290 K; used in vinegar; reacts with NaHCO₃ → CH₃COONa + CO₂ + H₂O; with ethanol + acid catalyst → ester (fruity smell) + H₂O (esterification).
- Soaps: sodium/potassium salts of long-chain carboxylic acids; form scum with hard water (Ca²⁺/Mg²⁺).
- Detergents: ammonium/sulphonate salts of long-chain hydrocarbons; work in hard water.
- Micelle: cluster of soap molecules with hydrophilic heads outside and hydrophobic tails inside — traps oil/dirt.
Formulas & key results
- Alkanes CₙH₂ₙ₊₂; Alkenes CₙH₂ₙ; Alkynes CₙH₂ₙ₋₂
- Combustion: hydrocarbon + O₂ → CO₂ + H₂O
- Ethanol → Ethene (H₂SO₄, 443 K, dehydration)
- CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O (esterification)
Mind map
- Covalent → allotropes → hydrocarbons → homologous series → functional groups
- Reactions: combustion, oxidation, addition, substitution, esterification
- Soaps vs detergents; micelle
Tricks & shortcuts
- IUPAC name: count C, identify bond, identify group.
- Addition reaction only for unsaturated compounds; substitution only for saturated.
Common mistakes to avoid
- Confusing addition vs substitution.
- Missing hydrogen atoms in structural formulas.
- Assuming detergents = soaps.
Competency-based questions & answers
- Q. Why do soaps not work well in hard water?A. Ca²⁺/Mg²⁺ ions form insoluble scum with soap → less lather → poor cleaning. Detergents avoid this because their calcium/magnesium salts are soluble.
- Q. Distinguish saturated from unsaturated hydrocarbons chemically.A. Add bromine water: unsaturated decolourises it (addition); saturated doesn't react. Or burn: unsaturated gives sooty flame.
- Q. Why is the conversion of ethanol to ethanoic acid an oxidation?A. Oxygen is added / hydrogen is removed. −OH group is converted to −COOH by the oxidising agent.