CBSE Class 10 · Science · board exam 2027
Chapter 4: Carbon and its Compounds — notes
The chapter’s 8 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. Bonding in carbon: the covalent bond
In the last chapter you studied ionic compounds, like sodium chloride.
- • Ionic compounds: high melting and boiling points; conduct in solution
- • Carbon compounds: low melting and boiling points; poor conductors
- • Low melting point ⇒ weak forces between molecules
- • Poor conductors ⇒ no ions are formed
- • C (atomic number 6): 2, 4
- • 4 valence electrons ⇒ needs 4 more for an octet
- • Gain 4 ⇒ C⁴⁻: a nucleus with 6 protons cannot hold 10 electrons
- • Lose 4 ⇒ C⁴⁺: needs a very large amount of energy
- • ∴ carbon forms no ions
- • Covalent bond: a bond formed by the sharing of an electron pair between two atoms
- • Covalent compounds: strong bonds inside the molecule, weak forces between molecules
- • H₂: one shared pair ⇒ H–H, single bond
- • O (2, 6): needs 2 ⇒ 2 shared pairs ⇒ O=O, double bond
- • N (2, 5): needs 3 ⇒ 3 shared pairs ⇒ N≡N, triple bond
- • CH₄: carbon shares one pair with each of the 4 hydrogens
- • C: 4 pairs = 8 electrons (octet); each H: 2 electrons (like helium)
- • Methane has 4 covalent bonds (C–H)
- • C₂H₄: 2 shared pairs between C and C (double bond), 1 with each H
- • Each C: 2 + 1 + 1 = 4 pairs = 8 electrons
2. The versatile nature of carbon: catenation and tetravalency
About three million carbon compounds are known today.
- • Catenation: the unique ability of carbon to form bonds with other atoms of carbon, giving large molecules
- • Long chains, branched chains, rings; the C–C bond is strong and stable
- • Silicon: chains of up to 7 or 8 atoms, very reactive
- • Tetravalency: carbon has a valency of 4
- • Small size ⇒ the nucleus holds the shared pairs strongly ⇒ strong bonds
- • Step 1: C–C (single bond)
- • Step 2: 3 H on the 3 free valencies of each C
- • Ethane: C₂H₆; 1 C–C + 6 C–H = 7 bonds
- • Propane: C₃H₈; 2 C–C + 8 C–H = 10 bonds
- • Saturated: only single bonds between carbon atoms (ethane)
- • Unsaturated: a double or triple bond between carbon atoms (ethene, ethyne)
- • Hydrocarbons: compounds of carbon and hydrogen only
- • | Basis | Alkane | Alkene | Alkyne |
- • | C–C bond | only single | a double | a triple |
- • | Nature | saturated | unsaturated | unsaturated |
- • | General formula | CₙH₂ₙ₊₂ | CₙH₂ₙ | CₙH₂ₙ₋₂ |
- • | Example | CH₄, C₂H₆ | C₂H₄ | C₂H₂ |
- • n = 2: alkane C₂H₆, alkene C₂H₄, alkyne C₂H₂
- • Unsaturated compounds are more reactive than saturated ones
3. Chains, branches, rings and isomers
Take four carbons, that is butane, C₄H₁₀.
- • C₄H₁₀: two skeletons, C–C–C–C (straight) and branched
- • Straight chain: 3 + 2 + 2 + 3 = 10 H
- • Branched chain: 3 + 3 + 3 + 1 = 10 H
- • Structural isomers: same molecular formula, different structures
- • Isomers of butane: n-butane, isobutane (2-methylpropane)
- • 3 carbons: only one skeleton, C–C–C ⇒ propane and propene have no structural isomer
- • Cyclohexane: a ring of 6 C, 2 H on each C ⇒ C₆H₁₂ (saturated)
- • Benzene: C₆H₆; in the ring 3 double + 3 single bonds; plus 6 C–H
- • Single bonds: 3 + 6 = 9; double bonds: 3
- • Cyclic hydrocarbons: cyclohexane, benzene
4. Functional groups, homologous series and nomenclature
In a carbon chain, a hydrogen can be replaced by another atom, like chlorine, oxygen or nitrogen.
- • Functional group: the atom or group of atoms that decides the properties of a carbon compound
- • Heteroatoms: Cl, Br, O, N, S
- • | Group | Formula |
- • | Halo (chloro, bromo) | –Cl, –Br |
- • | Alcohol | –OH |
- • | Aldehyde | –CHO |
- • | Ketone | >C=O |
- • | Carboxylic acid | –COOH |
- • Homologous series: a series of compounds in which the same functional group substitutes for hydrogen in carbon chains of different lengths
- • CH₃OH, C₂H₅OH, C₃H₇OH, C₄H₉OH (each differs by –CH₂–)
- • –CH₂–: 12 + 2 × 1 = 14 u
- • Physical properties (melting point, boiling point, solubility): show a gradation with mass
- • Chemical properties: similar (the same functional group)
- • Carbons: 1 meth, 2 eth, 3 prop, 4 but, 5 pent
- • | Group | Add | Example |
- • | Halogen | prefix chloro-, bromo- | chloropropane CH₃CH₂CH₂Cl |
- • | Alcohol | suffix -ol | propanol CH₃CH₂CH₂OH |
- • | Aldehyde | suffix -al | propanal CH₃CH₂CHO |
- • | Ketone | suffix -one | propanone CH₃COCH₃ |
- • | Carboxylic acid | suffix -oic acid | propanoic acid CH₃CH₂COOH |
- • | Double / triple bond | -ene / -yne | propene / propyne |
- • Example: CH₃–CO–CH₃
- • 3 carbons ⇒ propane; >C=O ⇒ ketone ⇒ -one
- • propane − e + one = propanone
5. Chemical properties: combustion, oxidation, addition, substitution
First, combustion.
- • Combustion: methane
- • methane + oxygen → carbon dioxide + water + heat + light
- • C + O₂ → CO₂ + heat + light
- • CH₄ + O₂ → CO₂ + H₂O (unbalanced)
- • | Element | Left side | Right side |
- • | C | 1 | 1 ✓ |
- • | H | 4 | 2 ✗ |
- • CH₄ + O₂ → CO₂ + 2H₂O (H balanced, O still unbalanced)
- • Right O: 2 + 2 = 4; left O: 2 ⇒ 2O₂
- • CH₄ + 2O₂ → CO₂ + 2H₂O
- • | Element | Left side | Right side |
- • | C | 1 | 1 ✓ |
- • | H | 4 | 4 ✓ |
- • | O | 4 | 4 ✓ |
- • CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) + heat + light
- • Type: combustion (burning in oxygen, heat and light given out)
- • Saturated: clean blue flame (complete combustion)
- • Unsaturated: yellow flame with black smoke (soot)
- • Limited air ⇒ incomplete combustion ⇒ sooty flame
- • ethanol + [O] → ethanoic acid + water
- • CH₃CH₂OH + 2[O] →[alkaline KMnO₄ + heat] CH₃COOH + H₂O
- • [O]: oxygen from the oxidising agent; KMnO₄, K₂Cr₂O₇: oxidising agents
- • | Element | Left side | Right side |
- • | C | 2 | 2 ✓ |
- • | H | 6 | 4 + 2 = 6 ✓ |
- • | O | 1 + 2 = 3 | 2 + 1 = 3 ✓ |
- • ethene + hydrogen → ethane
- • CH₂=CH₂ + H₂ →[Ni catalyst] CH₃–CH₃
- • Type: addition (H₂ adds at the double bond; unsaturated ⇒ saturated)
- • vegetable oil (unsaturated) + H₂ →[Ni] vanaspati ghee (saturated)
- • methane + chlorine → chloromethane + hydrogen chloride
- • CH₄ + Cl₂ →[sunlight] CH₃Cl + HCl
- • | Element | Left side | Right side |
- • | C | 1 | 1 ✓ |
- • | H | 4 | 3 + 1 = 4 ✓ |
- • | Cl | 2 | 1 + 1 = 2 ✓ |
- • Type: substitution (Cl takes the place of H)
6. Properties of ethanol
Two very important compounds, ethanol and ethanoic acid.
- • Ethanol: CH₃CH₂OH (C₂H₅OH), functional group –OH
- • Liquid at room temperature; soluble in water in all proportions; good solvent
- • Uses: tincture iodine, cough syrups, tonics
- • Absolute alcohol (pure ethanol): can be lethal; regular drinking harms health
- • sodium + ethanol → sodium ethoxide + hydrogen
- • Na + C₂H₅OH → C₂H₅ONa + H₂ (unbalanced)
- • | Element | Left side | Right side |
- • | Na | 1 | 1 ✓ |
- • | H | 6 | 5 + 2 = 7 ✗ |
- • 2Na + 2C₂H₅OH → 2C₂H₅ONa + H₂
- • | Element | Left side | Right side |
- • | Na | 2 | 2 ✓ |
- • | C | 4 | 4 ✓ |
- • | H | 12 | 10 + 2 = 12 ✓ |
- • | O | 2 | 2 ✓ |
- • 2Na(s) + 2C₂H₅OH(l) → 2C₂H₅ONa(aq) + H₂(g)
- • Gas: hydrogen (burns with a pop sound)
- • ethanol → ethene + water
- • CH₃CH₂OH →[hot conc. H₂SO₄, 443 K] CH₂=CH₂ + H₂O
- • Check: C₂H₆O = C₂H₄ + H₂O (C 2, H 6, O 1 on both sides)
- • Conc. H₂SO₄: dehydrating agent (removes water)
- • C₂H₅OH + O₂ → CO₂ + H₂O (unbalanced)
- • C: 2 ⇒ 2CO₂; H: 6 ⇒ 3H₂O
- • Right O: 4 + 3 = 7; left: 1 + 6 = 7 ⇒ 3O₂
- • C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l) + heat + light
7. Properties of ethanoic acid
Ethanoic acid, commonly called acetic acid.
- • Ethanoic acid (acetic acid): CH₃COOH, group –COOH
- • Vinegar: 5–8 % solution in water, a preservative in pickles
- • Pure ethanoic acid: melting point 290 K ⇒ freezes in winter ⇒ glacial acetic acid
- • Weak acid: not fully ionised, pH higher than a mineral acid like HCl
- • Activity: esterification
- • Aim: to make an ester from an acid and an alcohol
- • Materials: ethanol, ethanoic acid, conc. H₂SO₄, test tube, beaker, burner
- • Method: 1. In a test tube, 1 mL ethanol + 1 mL ethanoic acid + a few drops conc. H₂SO₄
- • 2. Warm in a water bath for 5 minutes 3. Pour into a beaker of water and smell
- • Observation: a sweet smell
- • Conclusion: ethanoic acid + ethanol → ester (ethyl ethanoate) + water
- • CH₃COOH + CH₃CH₂OH →[acid] CH₃COOC₂H₅ + H₂O
- • | Element | Left side | Right side |
- • | C | 2 + 2 = 4 | 4 ✓ |
- • | H | 4 + 6 = 10 | 8 + 2 = 10 ✓ |
- • | O | 2 + 1 = 3 | 2 + 1 = 3 ✓ |
- • ester + sodium hydroxide → sodium ethanoate + ethanol
- • CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH
- • | Difference | Esterification | Saponification |
- • | Reactants | acid + alcohol | ester + alkali (NaOH) |
- • | Products | ester + water | alcohol + salt of the acid |
- • | Use | perfumes, flavours | making soap |
- • ethanoic acid + sodium hydroxide → sodium ethanoate + water
- • CH₃COOH + NaOH → CH₃COONa + H₂O
- • | Element | Left side | Right side |
- • | C | 2 | 2 ✓ |
- • | H | 4 + 1 = 5 | 3 + 2 = 5 ✓ |
- • | O | 2 + 1 = 3 | 2 + 1 = 3 ✓ |
- • | Na | 1 | 1 ✓ |
- • Observation: brisk effervescence; the gas turns lime water milky ⇒ CO₂
- • ethanoic acid + sodium carbonate → sodium ethanoate + water + carbon dioxide
- • CH₃COOH + Na₂CO₃ → CH₃COONa + H₂O + CO₂ (unbalanced)
- • 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
- • | Element | Left side | Right side |
- • | Na | 2 | 2 ✓ |
- • | H | 8 | 6 + 2 = 8 ✓ |
- • | C | 4 + 1 = 5 | 4 + 1 = 5 ✓ |
- • | O | 4 + 3 = 7 | 4 + 1 + 2 = 7 ✓ |
- • CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂
- • | Element | Left side | Right side |
- • | Na | 1 | 1 ✓ |
- • | H | 4 + 1 = 5 | 3 + 2 = 5 ✓ |
- • | C | 2 + 1 = 3 | 2 + 1 = 3 ✓ |
- • | O | 2 + 3 = 5 | 2 + 1 + 2 = 5 ✓ |
- • Salt: sodium ethanoate (sodium acetate); alcohol: no effervescence
8. Soaps and detergents
Because oil does not dissolve in water.
- • Soap: sodium or potassium salt of a long-chain carboxylic acid
- • Example: sodium stearate C₁₇H₃₅COO⁻Na⁺
- • Ionic end (–COO⁻Na⁺): hydrophilic, dissolves in water
- • Hydrocarbon tail: hydrophobic, dissolves in oil
- • Micelle: a cluster of soap molecules in water, tails inside (in the oil), ionic ends outside (in the water)
- • Ion-ion repulsion between micelles ⇒ no precipitate, an emulsion forms
- • Rinsing carries the micelles with the dirt away ⇒ cleaning
- • Hard water: calcium and magnesium salts
- • X (soap): little foam, scum forms; Y (detergent): much foam
- • Soap + Ca²⁺, Mg²⁺ (hard water) ⇒ insoluble scum ⇒ little lather, more soap needed
- • Detergents: ammonium or sulphonate salts of long-chain carboxylic acids
- • No scum even in hard water, good lather
- • | Difference | Soap | Detergent |
- • | Nature | Na/K salt of a carboxylic acid | ammonium or sulphonate salt |
- • | In hard water | forms scum, little lather | no scum, good lather |
Summary
Very good! You learnt a lot today, so let us revise it once together. Carbon forms no ions, it shares electrons and forms covalent bonds, single, double and triple. Catenation and tetravalency give it millions of compounds, saturated and unsaturated, in chains, branches and rings, and with isomers. Then functional groups, homologous series and naming. Combustion, oxidation, addition and substitution, with every equation balanced. The reactions of ethanol and ethanoic acid, and at the end, the micelle of soap and why detergents work in hard water. Write all of today's equations in your notebook once, balancing each one without looking, and draw the structures of methane, ethanol, ethanoic acid and the isomers of butane. Today's homework is on your screen. If anything was not clear, press the Ask button and ask me. Done, you worked very well today!
AskMedha · Medha Ma’am — CBSE Class 10 Science, Chapter 4. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "Carbon and its Compounds" notes as a PDF?
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- From the chapter’s own textbook text, part by part, in the book’s own terms; a second, independent model then checked every part against the book. The full lesson, a check question for each part and the practice are in the AskMedha app.
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