Carbon and its Compounds Class 10 Notes (2026-27) — CBSE
Class 10 Science Chapter 4 revision notes: covalent bonding, catenation, homologous series, functional groups, ethanol and ethanoic acid, soaps and detergents.
Carbon and its Compounds — Class 10 Science Notes
Chapter Snapshot
Carbon is the element behind all living things and millions of compounds. This chapter explains why: its covalent bonding, tetravalency, and catenation. You then learn to classify and name hydrocarbons, identify functional groups, follow the main reaction types, study ethanol and ethanoic acid in detail, and understand how soaps and detergents clean.
Board relevance: reliably supplies a nomenclature or isomer question, an ethanol/ethanoic-acid reaction, and a soap/micelle question. Structural formulas earn marks — draw them clearly.
Key Concepts & Definitions
Covalent bond — a bond formed by the sharing of electrons between atoms so each attains a stable noble-gas configuration. Carbon has 4 valence electrons and shares all four (tetravalency), forming four covalent bonds. Covalent compounds have low melting/boiling points, are poor conductors (no free ions), and are usually insoluble in water.
Catenation — the ability of carbon atoms to bond with one another forming long chains, branched chains, and rings. Carbon–carbon bonds are strong, which is why carbon forms an enormous number of stable compounds.
Allotropes of carbon — different structural forms of the same element: diamond (each C bonded to 4 others, hardest natural substance), graphite (each C bonded to 3, in layers — soft, conducts electricity), and fullerene (e.g. C₆₀, ball-shaped).
Hydrocarbons — compounds of only carbon and hydrogen.
- Saturated (alkanes): only single bonds. General formula CₙH₂ₙ₊₂. Burn with a clean blue flame. e.g. methane CH₄, ethane C₂H₆.
- Unsaturated: contain double bonds (alkenes, CₙH₂ₙ, e.g. ethene C₂H₄) or triple bonds (alkynes, CₙH₂ₙ₋₂, e.g. ethyne C₂H₂). Burn with a sooty yellow flame; undergo addition.
Isomers — compounds with the same molecular formula but different structures (e.g. two structures of C₄H₁₀: n-butane and iso-butane).
Functional Groups and Homologous Series
A functional group is an atom or group that gives a compound its characteristic properties.
Functional group Name Example
−OH Alcohol Ethanol, C₂H₅OH
−CHO Aldehyde Ethanal, CH₃CHO
C=O Ketone Propanone, CH₃COCH₃
−COOH Carboxylic acid Ethanoic acid, CH₃COOH
−X (Cl, Br) Haloalkane Chloroethane, C₂H₅Cl
Homologous series — a family of compounds with the same functional group, where each member differs from the next by a −CH₂− unit (mass difference 14 u). Members share chemical properties; physical properties (boiling point, etc.) change gradually with chain length.
Nomenclature: name = prefix (number of carbons: meth-1, eth-2, prop-3, but-4) + suffix/functional-group indicator. Double bond → "-ene", triple bond → "-yne", alcohol → "-ol", acid → "-oic acid".
Chemical Properties
Reaction What happens Example
Combustion Hydrocarbons burn in air/O₂ releasing heat and light CH₄ + 2O₂ → CO₂ + 2H₂O + heat
Oxidation Alcohols oxidised to carboxylic acids by oxidising agents (alkaline KMnO₄, acidified K₂Cr₂O₇) C₂H₅OH →[O] CH₃COOH
Addition Unsaturated + H₂ over Ni catalyst → saturated (hydrogenation) Used to make vanaspati from vegetable oils
Substitution Saturated hydrocarbons react with Cl₂ in sunlight, H replaced by Cl CH₄ + Cl₂ →(sunlight) CH₃Cl + HCl
Saturated compounds usually undergo substitution; unsaturated compounds undergo addition.
Ethanol and Ethanoic Acid
Ethanol (C₂H₅OH)
- Common name: alcohol; a liquid at room temperature, neutral, good solvent.
- With sodium: 2C₂H₅OH + 2Na → 2C₂H₅ONa (sodium ethoxide) + H₂↑ (releases hydrogen gas — a test for the −OH group).
- Dehydration: heated with excess conc. H₂SO₄ at ~443 K, ethanol loses water to give ethene: C₂H₅OH → C₂H₄ + H₂O (H₂SO₄ acts as a dehydrating agent).
- Harmful effects: excessive drinking damages the liver; methanol is poisonous and can cause blindness/death.
Ethanoic acid (CH₃COOH, acetic acid)
- 5–8% solution in water is vinegar; pure form freezes on cold days → glacial acetic acid. It is a weak acid (partially ionised).
- With base: CH₃COOH + NaOH → CH₃COONa + H₂O (neutralisation).
- With carbonate/bicarbonate: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂↑ (brisk effervescence — distinguishes acids).
- Esterification: CH₃COOH + C₂H₅OH →(conc. H₂SO₄) CH₃COOC₂H₅ (ethyl ethanoate, a sweet-smelling ester) + H₂O. On heating with a base, an ester is hydrolysed back (saponification).
Soaps and Detergents
- Soap = sodium/potassium salt of a long-chain fatty acid. A soap molecule has a hydrophilic (water-loving) ionic head and a hydrophobic (water-hating) hydrocarbon tail.
- Micelle: in water, soap molecules form clusters with tails pointing inward (trapping oil/grease) and heads outward — the dirt is carried away when rinsed. This is how soap cleans.
- Hard water contains Ca²⁺ and Mg²⁺ salts; soap reacts with them to form insoluble scum, wasting soap.
- Detergents are ammonium/sulphonate salts; they do not form scum with hard water, so they clean effectively even in hard water and are used in shampoos and washing powders.
Important Question Patterns
1. Bonding/reasoning (2 marks): why carbon forms so many compounds (catenation + tetravalency); why covalent compounds have low melting points and don't conduct.
2. Nomenclature & isomers (2–3 marks): name a given structure; draw isomers of C₄H₁₀ or C₅H₁₂; identify the functional group.
3. Reaction (3 marks): ethanol + Na, dehydration to ethene, ethanoic acid + carbonate/base, esterification — write the equation and name the products.
4. Distinguishing test (2 marks): distinguish ethanol from ethanoic acid (add sodium carbonate → only the acid gives CO₂ effervescence).
5. Soap/detergent (2–3 marks): structure of a soap molecule; micelle formation with a diagram; why soap fails in hard water; soap vs detergent.
⚡ Quick Revision
- Carbon = covalent bonds + tetravalency + catenation → millions of compounds. Allotropes: diamond, graphite, fullerene.
- Alkanes CₙH₂ₙ₊₂ (single, saturated, blue flame, substitution); alkenes CₙH₂ₙ; alkynes CₙH₂ₙ₋₂ (double/triple, unsaturated, sooty flame, addition).
- Homologous series: same functional group, differ by −CH₂− (14 u).
- Functional groups: −OH alcohol, −CHO aldehyde, C=O ketone, −COOH acid.
- Ethanol: + Na → H₂↑; conc. H₂SO₄ heat → ethene (dehydration).
- Ethanoic acid (weak): + base → salt + water; + carbonate → CO₂↑ (test); + alcohol → ester (esterification, sweet smell).
- Reaction types: saturated → substitution (Cl₂/sunlight); unsaturated → addition (H₂/Ni = hydrogenation, makes vanaspati).
- Soap = hydrophilic head + hydrophobic tail → micelle traps grease. Hard water → scum; detergents work in hard water.
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