CBSE Class 10 Science Carbon and its Compounds Notes

Introduction to Carbon and its Compounds

Carbon and its Compounds is Chapter 4 of Class 10 Science and the most extensive chemistry chapter in the syllabus. Carbon is a unique element — it forms over 10 million known compounds, far more than any other element. This branch of chemistry dealing with carbon compounds is called organic chemistry.

The reason carbon can form such an enormous variety of compounds lies in two special properties: catenation (the ability of carbon atoms to bond with each other in long chains, branches, and rings) and tetravalency (carbon has 4 valence electrons and forms 4 covalent bonds, combining with C, H, O, N, S, halogens, and more).

This chapter covers the structure of carbon compounds, naming rules (IUPAC nomenclature), homologous series, important functional groups, chemical reactions of carbon compounds, and key organic compounds like ethanol and ethanoic acid that appear in daily life and board exams.

Key Topics Covered

•         Covalent Bonding in Carbon — Single, Double, Triple Bonds

•         Allotropes of Carbon — Diamond, Graphite, Fullerene

•         Catenation and Tetravalency — Why Carbon Forms So Many Compounds

•         Saturated and Unsaturated Carbon Compounds

•         Functional Groups and Homologous Series

•         IUPAC Nomenclature of Carbon Compounds

•         Chemical Reactions: Combustion, Oxidation, Addition, Substitution

•         Ethanol (Ethyl Alcohol) — Properties and Uses

•         Ethanoic Acid (Acetic Acid) — Properties and Uses

•         Soaps and Detergents — Micelle Formation and Cleansing Action

1.  Covalent Bonding and Allotropes of Carbon

Covalent Bonding in Carbon

Carbon has atomic number 6 and electronic configuration 2, 4 — meaning it has 4 valence electrons. To achieve the stable octet, carbon would need to either gain 4 or lose 4 electrons, both of which require enormous energy. Instead, carbon shares its 4 electrons with other atoms through covalent bonds.

•         Single bond (C–C): One shared pair of electrons. Present in alkanes (e.g., ethane C2H6). Longest bond length, lowest bond energy.

•         Double bond (C=C): Two shared pairs of electrons. Present in alkenes (e.g., ethene C2H4). Shorter and stronger than single bond.

•         Triple bond (C≡C): Three shared pairs of electrons. Present in alkynes (e.g., ethyne C2H2). Shortest and strongest C–C bond.

Allotropes of Carbon

Allotropes are different structural forms of the same element. Carbon exists in three main allotropes, each with dramatically different properties due to their bonding arrangement.

Diamond is the hardest natural substance but graphite is slippery — both are pure carbon! The difference is bonding structure, not composition.

2.  Catenation, Tetravalency and Types of Carbon Compounds

Catenation

Catenation is the unique ability of carbon atoms to form bonds with other carbon atoms, resulting in long chains, branched chains, and ring structures. No other element shows catenation to this extent. Silicon shows limited catenation.

•         Straight chain:  C–C–C–C–C–C  (e.g., n-hexane)

•         Branched chain:  C–C(C)–C–C  (e.g., isobutane, 2-methylpropane)

•         Ring/cyclic structure:  C atoms form closed rings (e.g., cyclohexane, benzene)

Tetravalency

Carbon has 4 valence electrons, so it forms 4 covalent bonds. These bonds can be with H, O, N, S, halogens (Cl, Br, I), or other carbon atoms. This versatility explains the sheer diversity of organic compounds.

Carbon: valency = 4  |  Forms 4 covalent bonds  |  Achieves octet by sharing

Saturated and Unsaturated Compounds

3.  Functional Groups and Homologous Series

Functional Groups

A functional group is an atom or group of atoms that determines the chemical properties of an organic compound. Compounds with the same functional group show similar chemical behaviour.

Homologous Series

A homologous series is a group of organic compounds that: (1) have the same functional group, (2) differ by a –CH2– unit (molecular mass differs by 14 u), (3) have the same general formula, (4) show a gradual change in physical properties, and (5) have similar chemical properties.

Members of a homologous series differ by –CH2– (14 u). Physical properties change gradually along the series; chemical properties remain similar.

4.  IUPAC Nomenclature of Carbon Compounds

IUPAC (International Union of Pure and Applied Chemistry) nomenclature provides a systematic method for naming organic compounds. The name conveys the structure of the compound.

Rules for IUPAC Naming

1.       Find the longest carbon chain containing the functional group — this is the parent chain. Count the number of carbons to get the prefix (meth=1, eth=2, prop=3, but=4, pent=5, hex=6).

2.       Number the chain from the end nearest the functional group (or substituent if no functional group).

3.       Identify the functional group and add the appropriate suffix: –ane (alkane), –ene (alkene), –yne (alkyne), –ol (alcohol), –al (aldehyde), –one (ketone), –oic acid (carboxylic acid).

4.       Name substituents (branches) as prefixes with their position numbers. Alphabetical order for multiple substituents.

5.       Combine: Position + substituent + parent chain + suffix.

Carbon Chain Prefixes

IUPAC naming example: CH3-CH2-OH = Ethanol (eth=2C, an=single bond, ol=alcohol functional group)

5.  Chemical Reactions of Carbon Compounds

Combustion

Carbon compounds burn in air/oxygen to produce CO2 and H2O, releasing heat and light energy. This is an oxidation reaction.

CnHm + O2  ->  CO2 + H2O + heat/light

CH4 + 2O2  ->  CO2 + 2H2O + heat           (complete combustion, blue flame)

C2H5OH + 3O2  ->  2CO2 + 3H2O + heat       (ethanol burns cleanly)

Insufficient O2  ->  CO (poisonous) + soot  (incomplete combustion)

Saturated compounds burn with a blue non-sooty flame. Unsaturated compounds burn with a yellow sooty flame (incomplete combustion due to high C content).

Oxidation

Carbon compounds can be oxidised by oxidising agents like alkaline KMnO4 or acidified K2Cr2O7 to form other functional group compounds.

CH3OH  --(KMnO4/K2Cr2O7)-->  HCOOH  (methanol oxidised to methanoic acid)

C2H5OH  --(KMnO4)-->  CH3COOH  (ethanol oxidised to ethanoic acid)

Alcohols -> Aldehydes -> Carboxylic acids  (progressive oxidation)

Alcohols are oxidised to carboxylic acids. This is why ethanol in wine turns to acetic acid (vinegar) on prolonged exposure to air.

Addition Reactions

Unsaturated compounds (alkenes, alkynes) undergo addition reactions where atoms add across the double or triple bond to form a saturated product.

Alkene + H2  --(Ni catalyst, heat)-->  Alkane   (hydrogenation)

CH2=CH2 + H2  --(Ni, heat)-->  CH3-CH3    (ethene + H2 -> ethane)

CH2=CH2 + Cl2  -->  CH2Cl-CH2Cl           (ethene + Cl2 -> 1,2-dichloroethane)

CH2=CH2 + HBr  -->  CH3-CH2Br             (ethene + HBr -> bromoethane)

•         Hydrogenation of oils: Vegetable oils (unsaturated) + H2 -> vegetable ghee (saturated fats) using Ni catalyst. Used in food industry.

Substitution Reactions

Saturated compounds (alkanes) undergo substitution reactions where one atom (usually H) is replaced by another atom (usually a halogen) in the presence of sunlight.

Alkane + Cl2  --(sunlight)-->  Chloroalkane + HCl

CH4 + Cl2  --(sunlight)-->  CH3Cl + HCl   (methane -> chloromethane + HCl)

CH3Cl + Cl2  --(sunlight)-->  CH2Cl2 + HCl (further substitution possible)

Esterification

Alcohols react with carboxylic acids in the presence of concentrated H2SO4 (acid catalyst) and on heating to form esters. Esters have pleasant fruity smell and are used in perfumes and flavourings.

Alcohol + Carboxylic acid  --(conc. H2SO4, heat)-->  Ester + Water

C2H5OH + CH3COOH  --(H2SO4)-->  CH3COOC2H5 + H2O

(Ethanol + Ethanoic acid -> Ethyl ethanoate + Water)

Saponification is the reverse of esterification: Ester + NaOH -> Alcohol + Sodium salt of acid (soap). This is how soaps are made.

6.  Ethanol and Ethanoic Acid

Ethanol (Ethyl Alcohol) — C2H5OH

Ethanol is the most important alcohol in everyday life. It is a colourless liquid with a pleasant smell and is miscible with water in all proportions.

•         Preparation: Fermentation of glucose using yeast: C6H12O6  -->(yeast)-->  2C2H5OH + 2CO2

•         Boiling point: 78 degrees C

•         Reacts with Na: 2C2H5OH + 2Na -> 2C2H5ONa + H2 (sodium ethoxide + hydrogen gas)

•         Oxidation: Ethanol -> Ethanoic acid (using alkaline KMnO4 or acidified K2Cr2O7)

•         Dehydration: C2H5OH --(conc. H2SO4, 170 deg C)--> CH2=CH2 + H2O (ethene formed)

•         Uses: Solvent, antiseptic, fuel (petrol blend), in medicines and perfumes, alcoholic beverages.

Denatured alcohol (methylated spirit) is ethanol with methanol and pyridine added to make it undrinkable. Methanol is highly toxic — causes blindness and death.

Ethanoic Acid (Acetic Acid) — CH3COOH

Ethanoic acid is the most common carboxylic acid. Dilute ethanoic acid (5–8%) is known as vinegar and is used as a food preservative and flavouring agent.

•         Boiling point: 118 degrees C

•         Melting point: 16.6 degrees C (pure ethanoic acid solidifies in winter — called glacial acetic acid)

•         Reacts with Na2CO3: 2CH3COOH + Na2CO3 -> 2CH3COONa + H2O + CO2 (brisk effervescence)

•         Reacts with NaOH: CH3COOH + NaOH -> CH3COONa + H2O (neutralisation; soap-making)

•         Esterification: CH3COOH + C2H5OH -> CH3COOC2H5 + H2O (ethyl ethanoate — fruity smell)

•         Uses: Vinegar (food preservative), manufacture of plastics, pharmaceuticals, dyes, as a solvent.

Pure ethanoic acid (glacial acetic acid) freezes at 16.6 degrees C, well above room temperature in cold regions. It melts when held in hand. This earns it the name 'glacial'.

7.  Soaps and Detergents

Soaps — Structure and Preparation

Soaps are sodium or potassium salts of long-chain fatty acids (carboxylic acids). They are made by the saponification of fats and oils with NaOH (for hard soap) or KOH (for soft/liquid soap).

Fat/Oil + NaOH  --(heat)-->  Soap (sodium salt of fatty acid) + Glycerol

•         Soap molecule structure: Long hydrocarbon tail (hydrophobic/non-polar, water-repelling) + carboxylate head (hydrophilic/polar, water-loving).

•         Sodium soaps: Hard soaps (used for washing clothes). Made with NaOH.

•         Potassium soaps: Soft/liquid soaps (shaving cream, hand wash). Made with KOH.

Micelle Formation and Cleansing Action

Soap works through a clever mechanism involving micelles — spherical clusters of soap molecules that trap dirt.

1.       Soap molecules arrange themselves at the oil-water interface: hydrophobic tails point INTO the oil droplet; hydrophilic heads point OUT towards water.

2.       This arrangement forms a spherical cluster called a MICELLE, with oil/grease trapped inside.

3.       The negatively charged heads on the outer surface of micelles repel each other, keeping micelles dispersed in water (this is called an emulsion).

4.       When rinsed with water, micelles (with trapped grease and dirt) are washed away, leaving the surface clean.

Micelle: Soap molecules surround a grease/oil droplet with hydrophobic tails inward (in grease) and hydrophilic heads outward (in water). The whole structure is washed away with water.

Soaps vs Detergents

8.  Key Reactions Summary

All important reactions from this chapter tested in CBSE Class 10 board examinations:

9.  Board Exam Practice Questions

These questions cover all types from CBSE Class 10 Science (Chapter 4) board examinations.

1 Mark Questions

1.       What is catenation? Why is carbon unique in showing this property?

2.       Give the IUPAC name of CH3COOH.

3.       What is the general formula of alkenes?

4.       Why does graphite conduct electricity but diamond does not?

5.       What is saponification?

3 Mark Questions

1.       Distinguish between saturated and unsaturated carbon compounds with two examples each. How can you test for unsaturation?

2.       What is a homologous series? List any four characteristics with an example series.

3.       Explain the cleansing action of soap. What is a micelle? Why do soaps not work in hard water?

4.       Write the chemical equation for esterification of ethanol with ethanoic acid. Name the product and describe its smell. How is esterification reversed?

5 Mark Questions

1.       Compare the allotropes of carbon (diamond, graphite, fullerene) under five headings: structure, bonding, hardness, electrical conductivity, and uses.

2.       Give the physical and chemical properties of ethanol and ethanoic acid with relevant chemical equations (at least 3 reactions for each).

3.       Explain with examples: (a) Combustion (b) Oxidation (c) Addition reaction (d) Substitution reaction of carbon compounds. Write one equation for each.