Carbon and its Compounds – Class 10 Science Chapter 4 Notes & NCERT PDF

Class 10ScienceChapter 4NCERT book: Science - Class 10

Notes and a simple summary of Chapter 4 of the NCERT Class 10 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 4: Carbon and its Compounds

Introduction

Food, clothes, medicines, books and many of the things around you contain carbon. The Earth's crust has only 0.02% carbon (as minerals like carbonates and coal) and the atmosphere has 0.03% CO₂, yet carbon forms more compounds than almost any other element. This chapter explains why: carbon's covalent bonding, tetravalency and catenation. You will learn homologous series, functional groups and naming, the main reactions of carbon compounds, the properties of ethanol and ethanoic acid, and how soaps and detergents clean.

Key Concepts

1. Covalent bonding in carbon

Carbon compounds have low melting and boiling points and are poor conductors — the forces between molecules are weak and they do not form ions.

Carbon (atomic number 6, electronic configuration 2, 4) would need to gain or lose 4 electrons to get a noble gas configuration — both are difficult. So it shares electrons.

A bond formed by sharing a pair of electrons is a covalent bond. Examples: H₂ (single bond), O₂ (double bond), N₂ (triple bond), CH₄ (four single C–H bonds).

Allotropes of carbon: diamond (each carbon bonded to four others — rigid 3-D structure, hardest substance), graphite (each carbon bonded to three others in hexagonal layers — smooth, slippery, good conductor of electricity), and fullerenes (C-60, shaped like a football; named after Buckminster Fuller).

2. Versatile nature of carbon

Catenation: carbon forms bonds with other carbon atoms, giving long chains, branches and rings.

Tetravalency: with valency 4, carbon bonds with carbon and with H, O, N, S, Cl etc. Its small size makes these bonds strong and stable.

Saturated hydrocarbons (alkanes) have only single bonds; unsaturated ones have double (alkenes) or triple (alkynes) bonds. Saturated compounds are generally less reactive.

Structural isomers – same molecular formula, different structures (e.g. butane has a straight-chain and a branched isomer, both C₄H₁₀).

Heteroatoms and functional groups: an atom replacing hydrogen gives a group that decides the properties — halo (–Cl, –Br), alcohol (–OH), aldehyde (–CHO), ketone (>C=O), carboxylic acid (–COOH).

3. Homologous series and nomenclature

A homologous series has the same functional group; successive members differ by –CH₂– (14 u). Alkanes: CH₄, C₂H₆, C₃H₈, C₄H₁₀ (general formula CₙH₂ₙ₊₂); alkenes CₙH₂ₙ; alkynes CₙH₂ₙ₋₂.

Members have similar chemical properties; physical properties like melting and boiling point increase gradually with molecular mass.

Naming: count carbons for the stem (meth-1, eth-2, prop-3, but-4, pent-5…), then add a prefix/suffix for the functional group: chloro- (chloropropane), -ol (propanol), -al (propanal), -one (propanone), -oic acid (propanoic acid), -ene (propene), -yne (propyne).

4. Chemical properties

Combustion: carbon compounds burn in oxygen to give CO₂, heat and light: CH₄ + 2O₂ → CO₂ + 2H₂O. Saturated hydrocarbons usually give a clean blue flame; unsaturated ones give a sooty yellow flame. Limited oxygen causes incomplete combustion (sooty flame, blackened vessels). Coal and petroleum formed from biomass over millions of years; burning them releases oxides of sulphur and nitrogen that cause acid rain.

Oxidation: alkaline potassium permanganate or acidified potassium dichromate (oxidising agents) convert ethanol to ethanoic acid; the purple colour of KMnO₄ disappears while it is being used up.

Addition reaction: unsaturated hydrocarbons add hydrogen in the presence of palladium or nickel catalysts. Hydrogenation of vegetable oils with nickel makes saturated fats (vanaspati). Vegetable oils with unsaturated fatty acids are healthier; animal fats are saturated and considered harmful.

Substitution reaction: saturated hydrocarbons are unreactive, but in sunlight chlorine replaces hydrogen: CH₄ + Cl₂ → CH₃Cl + HCl.

5. Ethanol (C₂H₅OH)

Liquid at room temperature, soluble in water, commonly called alcohol; active ingredient of drinks and used in tincture iodine, cough syrups and tonics.

Small amounts cause drunkenness; pure ethanol (absolute alcohol) is lethal; long-term use causes health problems. Methanol is extremely poisonous — it can cause blindness and death. Industrial ethanol is denatured by adding poisonous methanol and blue dye.

With sodium: 2Na + 2CH₃CH₂OH → 2CH₃CH₂O⁻Na⁺ + H₂ (hydrogen evolved; sodium ethoxide formed).

Dehydration: heating with excess concentrated H₂SO₄ at 443 K gives ethene: CH₃CH₂OH → CH₂=CH₂ + H₂O. Conc. H₂SO₄ is the dehydrating agent.

Ethanol from sugarcane is used as a clean fuel additive to petrol.

6. Ethanoic acid (CH₃COOH)

Called acetic acid; 5–8% solution in water is vinegar (used as a preservative in pickles). Pure ethanoic acid freezes in winter at 290 K, so it is called glacial acetic acid.

It is a weak acid (does not ionise completely), unlike HCl.

Esterification: ethanoic acid + ethanol with a little conc. H₂SO₄ gives a sweet-smelling ester (ethyl ethanoate); used in perfumes and flavouring.

Saponification: ester + NaOH → alcohol + sodium ethanoate (this is how soap is made).

With base: NaOH + CH₃COOH → CH₃COONa + H₂O.

With carbonates / hydrogencarbonates: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂.

7. Soaps and detergents

Soaps are sodium or potassium salts of long-chain carboxylic acids. A soap molecule has an ionic (hydrophilic) end that dissolves in water and a long carbon chain (hydrophobic) end that dissolves in oil.

In water, soap molecules form micelles: the hydrocarbon tails collect the oily dirt in the centre, the ionic ends face the water. The micelles stay in solution as a colloid and are rinsed away.

Hard water contains calcium and magnesium salts; soap reacts with them to form an insoluble scum, so more soap is needed.

Detergents are ammonium or sulphonate salts of long-chain carboxylic acids; they do not form scum in hard water, so they are used in shampoos and washing powders.

Important Reactions (balanced)

CH₄ + 2O₂ → CO₂ + 2H₂O (+ heat and light)

CH₃CH₂OH → CH₃COOH (alkaline KMnO₄ / acidified K₂Cr₂O₇, heat)

C₂H₄ + H₂ → C₂H₆ (Ni catalyst)

CH₄ + Cl₂ → CH₃Cl + HCl (sunlight)

2Na + 2CH₃CH₂OH → 2CH₃CH₂ONa + H₂

CH₃CH₂OH → CH₂=CH₂ + H₂O (hot conc. H₂SO₄, 443 K)

CH₃COOH + CH₃CH₂OH → CH₃COOC₂H₅ + H₂O (acid catalyst)

CH₃COOC₂H₅ + NaOH → C₂H₅OH + CH₃COONa

2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

Activities in the Chapter

Activity 4.1 – List household objects made of carbon compounds.

Activity 4.2 – Calculate the difference in formulae and molecular masses of successive members (methanol, ethanol, propanol, butanol) — each differs by CH₂ (14 u).

Activity 4.3/4.4 – Burn carbon compounds (camphor, alcohol) and compare flames: clean flame vs sooty flame; a gas stove's air holes.

Activity 4.5 – Warm ethanol with alkaline KMnO₄: the purple colour disappears.

Activity 4.7 – Compare pH of dilute acetic acid and HCl using litmus and universal indicator: acetic acid is weaker.

Activity 4.8 – Esterification: warm ethanol + glacial acetic acid + conc. H₂SO₄ and smell the fruity ester.

Activity 4.10 – Shake oil with water, then add soap: the oil layer disappears (emulsification).

Activity 4.12 – Compare foam of soap in distilled water and hard water; detergent forms foam in both.

Board Exam Focus

Electron-dot structures of CH₄, O₂, N₂, C₂H₄; why carbon forms covalent bonds.

Naming compounds from structural formulae and vice versa; identifying homologous series.

Distinguishing ethanol and ethanoic acid (sodium hydrogencarbonate test: CO₂ from the acid).

Mechanism of soap cleaning (micelles) and why soap fails in hard water.

Addition vs substitution reactions; hydrogenation of oils.

Key Terms

Covalent bond (सहसंयोजक आबंध)

Tetravalency (चतुःसंयोजकता)

Catenation (शृंखलन)

Allotrope (अपररूप)

Saturated / unsaturated hydrocarbon (संतृप्त / असंतृप्त हाइड्रोकार्बन)

Structural isomer (संरचनात्मक समावयव)

Functional group (प्रकार्यात्मक समूह)

Homologous series (समजातीय श्रेणी)

Oxidising agent (ऑक्सीकारक)

Addition reaction (संकलन अभिक्रिया)

Substitution reaction (प्रतिस्थापन अभिक्रिया)

Esterification (एस्टरीकरण)

Saponification (साबुनीकरण)

Micelle (मिसेल)

Detergent (अपमार्जक)

Common Mistakes

Saying carbon forms C⁴⁺ or C⁴⁻ ions — it forms covalent bonds by sharing.

Thinking graphite does not conduct electricity because it is a non-metal — graphite is a good conductor.

Mixing up addition (unsaturated compounds + H₂) and substitution (saturated compounds + Cl₂ in sunlight).

Calling ethanoic acid a strong acid — it is weak and ionises only partially.

Believing soap works well in hard water — it forms scum; detergents are used instead.

💡 Key Learning Points

✓Carbon forms covalent bonds by sharing electrons; its tetravalency and catenation give rise to a huge number of compounds.
✓Hydrocarbons are saturated (alkanes) or unsaturated (alkenes, alkynes); functional groups decide the properties of carbon compounds.
✓A homologous series has the same functional group and members differ by CH₂; compounds are named by the carbon stem plus functional-group prefix/suffix.
✓Carbon compounds undergo combustion, oxidation, addition (hydrogenation) and substitution reactions; ethanol and ethanoic acid have characteristic reactions like esterification.
✓Soaps clean by forming micelles but form scum in hard water; detergents work in hard water too.

👨‍🏫 Teaching Tips

→Use ball-and-stick or clay models to build methane, ethane, ethene and the two isomers of butane.
→Draw electron-dot structures of H₂, O₂, N₂ and CH₄ in sequence to show single, double and triple bonds.
→Make a naming chart (meth-, eth-, prop-, but- with -ol, -al, -one, -oic acid) and practise with flashcards.
→Compare a candle flame, a gas-stove flame and burning camphor to discuss complete and incomplete combustion.
→Perform the esterification activity (under supervision) so students smell the fruity ester.
→Demonstrate soap in distilled water vs hard water and draw a micelle trapping oil.
→Discuss denatured alcohol and the dangers of methanol to build health awareness.

📋 Assessment Questions

Draw the electron-dot structure of ethene and state the type of bond between the carbon atoms.
Name CH₃CH₂CHO and CH₃COCH₃.
What is hydrogenation? Where is it used?
How would you distinguish ethanol from ethanoic acid experimentally?
Explain the cleansing action of soap with a diagram of a micelle.

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