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Class 10 Carbon and its Compounds notes: NCERT Science Chapter 4 revision

CMDLearn · 3 November 2026

How much it counts

CBSE's Class 10 Science curriculum for 2026-27 puts Carbon and its Compounds in Unit I, Chemical Substances - Nature and Behaviour, worth 25 of the 80 theory marks, together with Chemical Reactions and Equations, Acids, Bases and Salts, and Metals and Non-metals (curriculum, page 4). For this chapter the unit lists covalent bonds, the versatile nature of carbon, saturated and unsaturated hydrocarbons, homologous series, naming, the four kinds of reaction, ethanol and ethanoic acid (properties and uses only), and soaps and detergents (page 5). CBSE gives marks per unit, not per chapter, so no one can honestly tell you an exact mark count for this chapter alone. More on the units: CBSE Class 10 Science syllabus 2026-27.

1. Why carbon matters (chapter opening, page 58)

• Food, clothes, medicines and all living things are built from carbon compounds.
• Yet carbon is scarce: the earth's crust holds only 0.02% carbon (in minerals such as carbonates, coal and petroleum), and the air has 0.03% carbon dioxide.

2. The covalent bond (section 4.1, pages 58-61)

• Carbon compounds mostly do not conduct electricity and have low melting and boiling points (Table 4.1, page 59). So the forces between their molecules are weak, and no ions are formed.
• Carbon has 4 electrons in its outer shell. Gaining 4 (C⁴⁻) or losing 4 (C⁴⁺) would both be very hard, so carbon shares its electrons instead (page 59).
• A shared pair of electrons is a covalent bond. One shared pair makes a single bond (H₂), two pairs a double bond (O₂), and three pairs a triple bond (N₂) (page 60).
• In methane, CH₄, carbon shares its four electrons with four hydrogen atoms. Carbon is tetravalent (page 60).
• The bonds inside a covalent molecule are strong, but the pull between molecules is weak. That explains the low melting and boiling points (pages 60-61).

Allotropes (page 61):

• In diamond, each carbon is bonded to four others in a rigid 3-D network. It is the hardest substance known.
• In graphite, each carbon is bonded to three others in flat hexagonal layers. It is slippery, and it conducts electricity, unlike other non-metals.
• Fullerenes: C-60 is shaped like a football and is named after the architect Buckminster Fuller.

3. Why there are millions of carbon compounds (section 4.2, pages 62-63)

Two properties work together:

1. Catenation: carbon bonds with other carbon atoms to form long chains, branched chains and rings. Silicon manages chains of only seven or eight atoms, and those compounds are very reactive (page 62).
2. Tetravalency: each carbon can bond with four other atoms, of carbon or of elements such as oxygen, hydrogen, nitrogen, sulphur and chlorine. Carbon's small size makes these bonds strong (page 62).

Friedrich Wöhler made urea from ammonium cyanate in 1828. That disproved the old idea that carbon compounds needed a 'vital force' from living things (page 63).

4. Saturated and unsaturated; chains, branches and rings (sections 4.2.1-4.2.2, pages 63-65)

• Saturated compounds have only single C–C bonds and are not very reactive. Unsaturated compounds have a double or triple bond and are more reactive (pages 63-64).
• Hydrocarbons contain only carbon and hydrogen. They come in three families (page 65): - alkanes have single bonds only; - alkenes have a double bond; - alkynes have a triple bond.
• The first six alkanes, methane to hexane (CH₄ to C₆H₁₄), are in Table 4.2 (page 64).
• Structural isomers have the same molecular formula but different structures. Butane, C₄H₁₀, has a straight-chain form and a branched form (page 65).
• Carbon can also form rings: cyclohexane is C₆H₁₂, and benzene is C₆H₆ (page 65).

5. Functional groups and homologous series (sections 4.2.3-4.2.4, pages 65-67)

• A heteroatom (a halogen, oxygen, nitrogen or sulphur) or a group containing it can take a hydrogen's place. Such groups are functional groups, and they decide the compound's chemical behaviour (Table 4.3, page 66).
• A homologous series is a family with the same functional group on carbon chains of different lengths, for example CH₃OH, C₂H₅OH, C₃H₇OH and C₄H₉OH (page 66).
• Each member differs from the next by –CH₂–, which is 14 u. Alkenes follow CₙH₂ₙ (page 67).
• Down a series, melting and boiling points rise with molecular mass, while the chemical properties stay similar (page 67).

6. Naming carbon compounds (section 4.2.5, pages 67-68)

1. Count the carbon atoms to get the base name: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6).
2. Add the functional group as a prefix or a suffix (Table 4.4, page 68):

| Group | Prefix or suffix | Example | |---|---|---| | Halogen | chloro-, bromo- | chloropropane | | Alcohol | -ol | propanol | | Aldehyde | -al | propanal | | Ketone | -one | propanone | | Carboxylic acid | -oic acid | propanoic acid | | Double bond | -ene | propene | | Triple bond | -yne | propyne |

1. If the suffix starts with a vowel, drop the final 'e' of the chain name: propane → propan + one = propanone (page 67).

7. Four kinds of reaction (section 4.3, pages 69-71)

• Combustion (page 69): carbon and most of its compounds burn in oxygen to give carbon dioxide, with heat and light. Saturated hydrocarbons usually burn with a clean flame. Unsaturated ones burn with a yellow, sooty flame. Too little air makes even saturated fuels sooty, which is why a blackened vessel bottom means blocked air holes (pages 69-70).
• Oxidation (pages 70-71): alkaline potassium permanganate or acidified potassium dichromate turn alcohols into carboxylic acids. Substances that add oxygen like this are oxidising agents.
• Addition (page 71): unsaturated hydrocarbons add hydrogen with a palladium or nickel catalyst. A catalyst changes how fast a reaction goes without being changed itself. Vegetable oils (unsaturated chains) are hydrogenated with nickel.
• Substitution (page 71): in sunlight, chlorine replaces the hydrogens of a saturated hydrocarbon one at a time: CH₄ + Cl₂ → CH₃Cl + HCl.

8. Ethanol and ethanoic acid (section 4.4, pages 72-74)

Ethanol (page 72):

• It is a liquid at room temperature, mixes with water in all proportions, and is a solvent in medicines such as tincture iodine and cough syrups.
• With sodium it gives off hydrogen and forms sodium ethoxide.
• Heated to 443 K with excess concentrated sulphuric acid, it loses water and gives ethene. The acid acts as a dehydrating agent.
• Denatured alcohol is industrial ethanol made unfit to drink with methanol and a blue dye. Methanol even in small amounts can kill or cause blindness.

Ethanoic acid (acetic acid; pages 73-74):

• It is a weak carboxylic acid, unlike fully ionised HCl. Vinegar is a 5-8% solution of it in water. Pure ethanoic acid melts at 290 K, so it can freeze in cold winters: hence "glacial acetic acid".
• Esterification: with ethanol and an acid catalyst it gives a sweet-smelling ester. Saponification turns an ester back into the alcohol and a sodium salt with NaOH; this is how soap is made.
• With NaOH it gives sodium ethanoate and water.
• With carbonates and hydrogencarbonates it gives a salt, carbon dioxide and water.

9. Soaps and detergents (section 4.5, pages 74-76)

• A soap molecule is the sodium or potassium salt of a long-chain carboxylic acid. Its ionic end is hydrophilic (it faces the water) and its carbon tail is hydrophobic (it faces the oil) (page 75).
• In water, soap molecules gather into micelles: tails inside around the oily dirt, ionic ends outside. The dirt is then rinsed away. Micelles scatter light, so soap solution looks cloudy (page 75).
• In hard water, soap reacts with calcium and magnesium salts to form scum, wasting soap. Detergents (usually sodium sulphonates, or ammonium salts carrying chloride or bromide ions, each with a long hydrocarbon chain) do not form such solids, so they keep working (page 76).

Key words at a glance

The diagram to know: a soap micelle

Fig. 4.12 (page 74) shows the soap micelle. To draw it from memory:

1. Draw an oil droplet as a circle.
2. Draw soap molecules around it as "tadpoles": the tails point into the oil and the round ionic heads sit on the outside, in the water.
3. Label "hydrophobic tail", "ionic (hydrophilic) end", "oily dirt" and "water".

Mistakes that cost marks

1. Counting bonds: count the C–C bonds and the C–H bonds separately, then add them. A chain of n carbons has n − 1 C–C bonds.
2. Calling any two molecules with the same atoms "isomers": the molecular formula must be exactly the same.
3. Writing "propaneone": drop the final 'e' before a suffix that starts with a vowel.
4. Mixing up addition and substitution: addition needs a double or triple bond and adds atoms. Substitution swaps one atom for another.
5. Calling ethanoic acid a strong acid: carboxylic acids are weak acids.

Quick check: 8 questions of our own

Try each on paper first. These are our own questions, not the textbook's.

Question 1. Butane, C₄H₁₀, has a straight chain of four carbon atoms and only single bonds. How many covalent bonds are in one molecule?

Answer: 13. The chain of 4 carbons has 3 C–C bonds, and each of the 10 hydrogens is joined by one C–H bond. 3 + 10 = 13. Check: each carbon ends up with four bonds. (Table 4.2, page 64; covalent bonds, page 60.)

Question 2. Which of these pairs are structural isomers? (a) Cyclohexane, C₆H₁₂, and hexene, C₆H₁₂. (b) Hexane, C₆H₁₄, and cyclohexane, C₆H₁₂. (c) Straight-chain butane and branched butane, both C₄H₁₀.

Answer: (a) and (c). Both pairs have exactly the same molecular formula but different structures: a ring against a chain with a double bond in (a), and a straight against a branched chain in (c). Pair (b) has different formulae (14 against 12 hydrogens), so the two are not isomers. (Isomers and rings, page 65.)

Question 3. Name each compound: (a) a four-carbon chain with an –OH group; (b) a four-carbon chain with a –COOH group; (c) a five-carbon chain with one double bond; (d) a two-carbon chain in which one hydrogen is replaced by chlorine; (e) a four-carbon chain with an aldehyde group.

Answer: (a) butanol; (b) butanoic acid; (c) pentene; (d) chloroethane; (e) butanal. Each takes the chain name (but-, pent-, eth-) plus the prefix or suffix from Table 4.4 (page 68), dropping the final 'e' before a suffix that starts with a vowel.

Question 4. Four fuels are tested: pentane (C₅H₁₂), butene (C₄H₈), propyne (C₃H₄) and hexane (C₆H₁₄). (a) Which two would add hydrogen in the presence of a nickel catalyst? (b) Which two are more likely to burn with a yellow, sooty flame?

Answer: (a) and (b) are the same two, butene and propyne.

• Butene has a double bond and propyne a triple bond, so both are unsaturated. Only unsaturated hydrocarbons take part in addition reactions (page 71).
• Unsaturated compounds usually burn with a yellow, sooty flame, while saturated ones like pentane and hexane burn cleanly in enough air (page 69).
• Check with the formulae: pentane and hexane fit CₙH₂ₙ₊₂ (12 = 2×5 + 2; 14 = 2×6 + 2).

Question 5. A student heats ethanol to 443 K with excess concentrated sulphuric acid. (a) Which gas is formed? (b) Write the equation and check that it balances. (c) What job does the sulphuric acid do?

Answer:

• (a) Ethene, C₂H₄ (page 72).
• (b) CH₃CH₂OH → CH₂=CH₂ + H₂O. Check: C 2 = 2, H 6 = 4 + 2, O 1 = 1.
• (c) It is a dehydrating agent: it removes water from the ethanol.

Question 6. Use Table 4.1 (page 59), where 0 °C = 273 K. (a) Which of the four compounds is a gas at a room temperature of 25 °C (298 K)? (b) On a cold morning at 10 °C, is pure acetic acid solid or liquid? (c) Which compound stays liquid over the widest temperature range?

Answer:

• (a) Methane. Its boiling point is 111 K, far below 298 K. The other three boil above 298 K and melt below it, so they are liquids.
• (b) Solid. 10 °C = 283 K, which is below acetic acid's melting point of 290 K. This is why it is called glacial acetic acid (page 73).
• (c) Ethanol. It is liquid from 156 K to 351 K, a range of 195 K. Chloroform's range is 334 − 209 = 125 K, and acetic acid's is 391 − 290 = 101 K.

Question 7. In sunlight, methane and chlorine give CH₃Cl and HCl. The chapter says chlorine replaces hydrogen atoms one by one. (a) Write the balanced equation for the next step, when CH₃Cl reacts with more chlorine. (b) How many such steps does it take to replace all four hydrogens? (c) What kind of reaction is this?

Answer:

• (a) CH₃Cl + Cl₂ → CH₂Cl₂ + HCl. Check: C 1 = 1, H 3 = 2 + 1, Cl 3 = 2 + 1.
• (b) Four steps, one for each hydrogen, ending with CCl₄.
• (c) A substitution reaction: one kind of atom takes the place of another (page 71).

Question 8. (a) The earth's crust has 0.02% carbon. On average, how many grams of carbon are there in 5 kg of crust? (b) In which allotrope is each carbon bonded to four other carbons, and in which to three? Which of the two conducts electricity?

Answer:

• (a) 5 kg = 5,000 g, and 0.02% of 5,000 g = 5,000 × 0.02 ÷ 100 = 1 g (page 58).
• (b) Diamond: four bonds per carbon in a rigid 3-D network. Graphite: three bonds per carbon in flat layers. Graphite conducts electricity (page 61).

Revise with questions

• Class 10 Carbon and its Compounds: 8 practice questions with answers
• The chapter before this one, in notes form: Class 10 Metals and Non-metals notes
• Free practice, marked instantly: Class 10 Carbon and its Compounds questions

Where CMDLearn fits

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Sources

All opened and read on 3 November 2026. Page numbers are the printed page numbers of the textbook.

• NCERT, Science, Textbook for Class X, Chapter 4 "Carbon and its Compounds" (Reprint 2026-27), printed pages 58-78: ncert.nic.in/textbook/pdf/jesc104.pdf
• CBSE, Science (086), Class X 2026-27, course structure (page 4) and Unit I contents (page 5): cbseacademic.nic.in/web_material/CurriculumMain27/SecPart1/Science_SecP1_2026-27.pdf

The facts, tables and page numbers are from the documents above. The notes, their order and wording, the questions and the worked answers are our own; every count and equation was re-checked by script.

Practise this class: Class 10 worksheets, chapter by chapter · free practice, marked instantly · timed revision papers