Carbon and Its Compounds — Complete CBSE Class 10 Notes

Carbon and Its Compounds Class 10 Notes (CBSE / NCERT): This chapter explains the basics of organic chemistry such as covalent bonding, hydrocarbons, functional groups, ethanol, ethanoic acid, soaps and detergents. These notes are prepared according to the latest CBSE Class 10 Science syllabus and follow NCERT textbook concepts.

All topics are explained in board-answer format so that students can learn and directly write in exams. Previous Year Questions (PYQ), important reactions, diagrams, naming rules, and questions are included to help students score full marks in board examinations.

Contents

1. Basic Facts about Carbon
2. Versatility of Carbon
3. Polymerisation & Isomerism
4. Covalent Bonding & Properties
5. Types of Covalent Bonds
6. Allotropes: Diamond, Graphite & Fullerene
7. Hydrocarbons
8. Functional Groups & IUPAC
9. Homologous Series
10. Isomerism & Electron-dot
11. Important Reactions
12. Ethanol
13. Ethanoic Acid & Esters
14. Soaps & Detergents
15. PYQs (Model Answers)
16. One-Page Revision

1. Basic Facts about Carbon

Carbon (C): Atomic number = 6, atomic mass ≈ 12 u. Electronic configuration = 2, 4. Carbon is a non-metal and valency = 4 (forms 4 covalent bonds).

Note: Number of protons = number of neutrons = 6 (in most common isotope).

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2. Uniqueness / Versatility of Carbon — Why so many compounds?

Board Answer (3 marks)

1. Tetravalency: Carbon has four valence electrons and forms 4 covalent bonds with atoms like H, O, N, halogens, allowing many combinations.
2. Catenation: Carbon atoms form strong C–C bonds to make long chains, branched chains and rings, increasing structural variety.
3. Multiple bonding: Carbon can form single (C–C), double (C=C) and triple (C≡C) bonds, creating saturated and unsaturated compounds.
4. Isomerism: Compounds having the same molecular formula but different structures (isomers) further increase the number of distinct compounds.

Conclusion: These properties together make carbon capable of forming millions of organic compounds; organic chemistry is studied separately for this reason.

Mark guidance: 1 mark = any one reason; 2 marks = two short points; 3 marks = above answer.

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3. Polymerisation and Isomerism (Definitions)

Polymerisation: Process in which small molecules (monomers) join to form large molecules (polymers) — e.g., ethene → polyethylene.

Isomerism: Phenomenon where compounds with same molecular formula have different structures (structural isomers) or different spatial arrangements (stereoisomers). Example: C₄H₁₀ → n-butane and isobutane.

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4. Covalent Bonding & Properties of Covalent Compounds

Board Answer (2–3 marks)

Covalent bond: Formed by sharing of electron pairs between atoms for stability. Carbon forms covalent bonds due to its 4 valence electrons.

Properties of covalent compounds

• Usually low melting & boiling points (due to weak intermolecular forces), except network solids (diamond).
• Poor conductors of electricity (no free ions/electrons) — exception: graphite.
• Solubility: Usually insoluble in water; soluble in organic solvents.
• Exist in all physical states: solids, liquids or gases.

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5. Types of Covalent Bonds

Single bond: one pair shared (C–C).
Double bond: two pairs shared (C=C).
Triple bond: three pairs shared (C≡C).

These influence reactivity: double/triple bonds are more reactive (addition reactions).

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6. Allotropes of Carbon: Diamond, Graphite & Fullerene

Board Answer — Describe structure & properties

Diamond: Each carbon is tetrahedrally bonded to four other carbons forming a 3D giant covalent network → extremely hard, transparent, high melting point, electrical insulator (no free electrons). Uses: gemstones, cutting tools.

Graphite: Each carbon bonded to three others forming hexagonal layers; one electron per carbon is delocalised → conducts electricity; layers held by weak forces → soft and slippery, good lubricant; used in pencil leads and electrodes.

Fullerene (C₆₀): Molecules form hollow cage-like spheres (soccer-ball shape). Unique electronic properties; used in research, nanotech, medicine (experimental).

Structure of graphite

PYQ: "Graphite conducts electricity but diamond does not. Explain."
Answer: In graphite each carbon atom is bonded to only three atoms, leaving one free electron. These free electrons are delocalized and can move freely throughout the structure, allowing electrical conductivity. In diamond all electrons are used in four covalent bonds leaving no free electrons that's why diamond does not conduct electricity.

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7. Hydrocarbons — Aliphatic & Aromatic; Alkanes, Alkenes, Alkynes

Board Answer (3 marks)

Hydrocarbon: Compound containing only C and H.

Aliphatic hydrocarbons

• Alkanes (saturated): Only single bonds; general formula C_nH_2n+2. Example: Ethane C₂H₆.
• Alkenes (unsaturated): Contain C=C double bond; general formula C_nH_2n. Example: Ethene C₂H₄.
• Alkynes (unsaturated): Contain C≡C triple bond; general formula C_nH_2n−2. Example: Ethyne C₂H₂.

Saturated hydrocarbons are more stable and less reactive, while unsaturated hydrocarbons are more reactive due to the presence of multiple bonds.

Types of carbon chain:

• Straight chain
• Branched chain
• Cyclic (ring) — e.g., cyclohexane, benzene (aromatic)

PYQ (2023 style): "Which of these belongs to alkynes?" (Options: C₆H₆, C₂H₆, C₂H₄, C₃H₄) — Answer: C₃H₄ (fits C_nH_2n−2 with n=3).

Formulae and structure of saturated compounds (Alkane):

Formulae and structure of unsaturated compounds (Alkene):

Formulae and structure of unsaturated compounds (Alkyne):

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8. Functional Groups & IUPAC Naming (Detailed)

Board Answer (4 marks)

Functional group: A specific group of atoms within a molecule that confers characteristic chemical properties.

 — e.g., –OH (alcohol), –COOH (carboxylic acid), –CHO (aldehyde), –CO– (ketone), –Cl/–Br (haloalkane).

IUPAC naming quick method

1. Find the longest carbon chain → base name (meth-, eth-, prop-, but-).
2. Number the chain to give functional group the lowest possible number.
3. Use appropriate suffix: –ane, –ene, –yne, –ol (alcohol), –oic acid (acid), –al (aldehyde), –one (ketone).
4. If suffix starts with vowel, drop final 'e' of hydrocarbon name (e.g., propanone not propaneone).

Examples (model answers)

Formula	IUPAC name
CH₃CH₂OH	Ethanol
CH₃COCH₃	Propanone
CH₃CH=CH₂	Propene
HCOOH	Methanoic acid
CH₃CH₂COOH	Propanoic acid
CH₃CHO	Ethanal
CH₃COOH	Ethanoic acid
CH₃CH₂CH₂Br	1-Bromopropane
CH₃C≡CH	Propyne
CH₂=CHCH₂Cl	3-Chloropropene

PYQ: "Write IUPAC names of: (i) CH₃CH₂OH (ii) CH₃COCH₃ (iii) CH₃CH=CH₂" 

— Answers: Ethanol; Propanone; Propene.

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9. Homologous Series 

A homologous series is a group of organic compounds with a similar general formula, functional group, and chemical properties, differ by a CH₂ unit in their molecular structure. 

Example: 

CH₃OH (Methanol) 

C₂H₅OH (Ethanol) 

C₃H₇OH (Propanol) 

— Characteristics

Board Answer (2–3 marks)

• Members have same functional group and general formula.
• Successive members differ by a –CH₂– unit (mass difference ≈ 14 u).
• Show gradation in physical properties (e.g., boiling point increases with molecular mass) while chemical properties are similar.

PYQ: 

Consider the following statements about the homologous series of carbon compounds: : 

(a) successive members differ by CH₂; 

(b) melting point & boiling point increase with decreasing molecular mass; 

(c) difference in mass = 14 u; 

(d) C₂H₂ and C₃H₃ are not successive members of alkyne series. 

Correct statements: both (a) & (c). 

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10. Isomerism — Short Examples & Electron-Dot Structures

Board Answer (short)

Definition: Isomers are compounds with same molecular formula but different structural arrangements and properties.

Example: Butane isomers

Pentane isomers

Electron-dot structures to practice

(i) Ethane C₂H₆ — single bond

(ii) Ethene C₂H₄ — double bond

(iii) Ethyne C₂H₂ — triple bond

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11. Important Chemical Reactions of Carbon Compounds

Combustion: Carbon burns in oxygen to give carbon dioxide along with the release of heat and light.

Complete combustion: Occurs in an unlimited supply of air, oxygen in particular. Here the hydrocarbon will burn out completely with the oxygen and leave only two byproducts, water, and carbon dioxide. E.g., burning of a candle.

Hydrocarbon + O₂ (sufficient) → CO₂ + H₂O + Heat. 

Incomplete combustion: Limited O₂ → CO (carbon monoxide) and soot (C) + H₂O — dangerous (CO poisonous) and soot forms.

Oxidation

Alcohols can be oxidised to aldehydes and further to carboxylic acids using oxidising agents such as alkaline KMnO₄ or acidified K₂Cr₂O₇.

Addition reactions

(Vegetable Ghee), Unsaturated hydrocarbons (C=C, C≡C) undergo addition to get a (vegetable oil) saturated hydrocarbon (C–C) in presence of Ni/Pd catalyst.

Substitution reactions

Alkanes undergo substitution, in the presence of sunlight, chlorine is added to hydrocarbons. Chlorine can replace the hydrogen atoms one by one. 

PYQ: "Write balanced equation for complete combustion of ethanol." — Answer: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.

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12. Ethanol (C₂H₅OH) — Properties, Reactions & Effects

Board Answer (3–4 marks)

Physical properties: Ethanol is a volatile liquid, miscible with water in all proportions, and a good solvent. Used in cough syrups, tincture iodine and tonics.

Chemical Reactions

• Combustion: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + energy.
• Reaction with sodium: Ethanol reacts with sodium, producing hydrogen gas and sodium ethoxide. 2Na + 2C₂H₅OH → 2C₂H₅O⁻Na⁺ + H₂ 
• Dehydration (conc. H₂SO₄ at 443 K): Ethanol is heated with excess concentrated sulphuric acid at 443 K, leading to the removal of water (dehydration) and formation of ethene. 
  Sulfuric acid acts as dehydrating agent.

• Oxidation: Ethanol → Ethanal → Ethanoic acid (with oxidising agents).

Effects on human body:

Excess ethanol depresses the central nervous system causing lack of coordination, drowsiness, impaired judgment; chronic abuse damages liver. 

Methanol (not ethanol) is highly toxic — even small amounts cause blindness and can be fatal; methanol oxidises to formaldehyde and formic acid in the body. Coagulates protoplasm, similar to how an egg solidifies when cooked. 

Denatured Alcohol: Ethanol is used as an industrial solvent, but to prevent misuse, it is denatured. Methanol and dyes are added to make it poisonous and easily identifiable (blue color).

PYQ: "State two uses of ethanol." — Answer: (1) Solvent in medicines and tinctures,  (2) Fuel and in alcoholic beverages (industrial & beverage uses).

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13. Ethanoic Acid (CH₃COOH) & Esters

Board Answer (3–4 marks)

Ethanoic acid: 

• Also called acetic acid; belongs to carboxylic acid functional group, 
• 5-8% solution in water is called vinegar, used as a preservative in pickles. 
• Melting point: 290 K; freezes in winter, hence called glacial acetic acid. 
• Weak acid compared to mineral acids like HCl (does not fully ionize in water).

Important reactions

• Neutralisation with base: Reacts with sodium hydroxide to form sodium ethanoate (sodium acetate) and water. CH₃COOH + NaOH → CH₃COONa + H₂O.
• Reaction with carbonates/hydrogencarbonates: 

CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂ (effervescence).

• Esterification: Reacts with ethanol in the presence of concentrated H₂SO₄ to form ester (ethyl ethanoate). Ester has a fruity smell and is used in perfumes and flavouring.

• Saponification: Ester + NaOH → salt of carboxylic acid + alcohol (used in soap-making).

PYQ: "An organic compound X (C₂H₄O₂) used as preservative in pickles reacts with ethanol to form a sweet-smelling compound Y. Identify X and Y. Give equation and name the process."
Answer: X = Ethanoic acid (CH₃COOH), Y = Ethyl ethanoate (CH₃COOC₂H₅);                        Equation: CH₃COOH + C₂H₅OH ⇄ CH₃COOC₂H₅ + H₂O;                                                              Process = Esterification (conc. H₂SO₄ as catalyst/dehydrating agent).

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14. Soaps, Detergents & Cleansing Action

Board Answer (3–4 marks)

Soaps: Sodium or potassium salts of long-chain carboxylic acids (e.g., sodium stearate). A soap molecule has:

• Hydrophilic head (ionic −COO⁻Na⁺) — water-loving.
• Hydrophobic tail (long hydrocarbon chain) — oil-loving.

Micelle formation: In water, soap molecules arrange themselves to form micelles. 

Micelle Structure:

• hydrophobic tails face inward trapping the oil; 
• hydrophilic heads face outward to water.

Cleaning Action of Soap: The dirt is emulsified into micelles and suspended in water, so it can be rinsed away.

Soaps vs Detergents

Soap	Detergent
Made from fatty acid salts (sodium/potassium)	Synthetic sulfonates/sulfates or ammonium salts
Weak cleansing action, Forms scum with hard water (Ca²⁺/Mg²⁺)	Strong cleansing action,Works in hard water (does not form scum)
Biodegradable (mostly)	Many are non-biodegradable → environmental pollution

PYQ: "Why soaps do not work well in hard water?"
Answer: Hard water contains Ca²⁺ and Mg²⁺ ions that react with soap to form insoluble scum, reducing the soap's cleansing action.

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15. Common Chemical Equations (Important to Memorize)

1. Combustion (methane): CH₄ + 2O₂ → CO₂ + 2H₂O + heat
2. Combustion (ethanol): C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
3. Oxidation (ethanol → ethanoic acid): C₂H₅OH + O → CH₃COOH + H₂O (with KMnO₄ / K₂Cr₂O₇)
4. Dehydration (ethanol → ethene): C₂H₅OH → CH₂=CH₂ + H₂O (conc. H₂SO₄, heat)
5. Saponification: CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH
6. Neutralisation: CH₃COOH + NaOH → CH₃COONa + H₂O
7. Esterification: CH₃COOH + C₂H₅OH ⇄ CH₃COOC₂H₅ + H₂O (conc. H₂SO₄)

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16. Compiled Previous Year Questions (PYQs) — Model Answers

1. Graphite vs Diamond — explain conductivity difference.
   Model Answer: Graphite: each C bonded to 3 carbons, one delocalised electron per atom that moves freely → conducts. Diamond: each C bonded to 4 carbons, no free electrons → does not conduct. (2 marks)
2. Why soaps do not work in hard water?
   Model Answer: Hard water contains Ca²⁺/Mg²⁺ which react with soap to form insoluble scum; scum reduces cleansing action. (1–2 marks)
3. Write the equation for esterification between ethanoic acid and ethanol.
   Model Answer: CH₃COOH + C₂H₅OH ⇄ CH₃COOC₂H₅ + H₂O (conc. H₂SO₄ as catalyst). (2 marks)
4. Define homologous series with example.
   Model Answer: A homologous series is a group of compounds with the same functional group and general formula, differing by CH₂ unit. Example: Methanol, Ethanol, Propanol. (2–3 marks)
5. Complete combustion of ethanol — balanced equation.
   Model Answer: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. (2 marks)
6. Why is ethanol used as a solvent?
   Model Answer: Ethanol can dissolve both polar (because of –OH) and some non-polar substances (because of ethyl group), making it a versatile solvent. (1–2 marks)

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17. Practice for Board Examination

1. Functional group in ethanol? — (–OH)
2. General formula of alkanes? — C_nH_2n+2
3. Explain why vegetable oils (unsaturated) become solid on hydrogenation. — Addition of H across C=C bonds converts unsaturated fatty acids to saturated ones, increasing melting point → solidifies.
4. Explain why coal/charcoal burn with red glow but no flame. — They lack volatile constituents; combustion is surface oxidation producing heat & red glow without flame (flame requires volatile vapours).

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18. Most Important Lines to Memorise

• Tetravalency + catenation + isomerism + multiple bonding = vast organic chemistry.
• Alkanes: C_nH_2n+2; Alkenes: C_nH_2n; Alkynes: C_nH_2n−2.
• Diamond: tetrahedral (hard, insulator); Graphite: layered (conducts, lubricant).
• Ethanol combusts to CO₂ + H₂O; oxidises to ethanoic acid; reacts with sodium to release H₂.
• Ethanoic acid + ethanol (conc. H₂SO₄) → ester (sweet smell) + water.
• Soaps form micelles: hydrophobic tails trap grease, hydrophilic heads face water.

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19. Exam Writing Tips & Keywords to Use

• Begin answers with definitions: e.g., "Catenation is..." or "Isomerism is..."
• Use keywords: tetravalency, delocalised electrons, micelle, esterification, dehydrating agent, oxidation, saponification.
• Where asked for reason, always give a cause + effect sentence (examiner-friendly).
• Write equations balanced, name reagents (e.g., KMnO₄ / conc. H₂SO₄ / NaOH).
• For 5-mark answers: include small labelled diagrams (electron-dot or structural) and one example.

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