Carbon and its Compounds

Complete Chapter Notes in Simple Language

Chapter Overview: This chapter explains covalent bonding in carbon, the versatile nature of carbon (catenation and tetravalency), saturated and unsaturated compounds, homologous series and nomenclature, the chemical properties of carbon compounds (combustion, oxidation, addition and substitution reactions), ethanol and ethanoic acid, and soaps and detergents.

📚 Chapter Contents

• Bonding in Carbon — The Covalent Bond
• Bonding in Simple Molecules
• Allotropes of Carbon
• Versatile Nature of Carbon
• Saturated and Unsaturated Compounds
• Chains, Branches and Rings
• Functional Groups
• Homologous Series
• Nomenclature of Carbon Compounds
• Combustion
• Oxidation
• Addition Reaction
• Substitution Reaction
• Ethanol
• Ethanoic Acid
• Esterification & Saponification
• Soaps and Detergents
• 20 Important Questions

Most carbon compounds are poor conductors of electricity and have low melting and boiling points compared to ionic compounds. This tells us that the forces between their molecules are weak and that their bonding does not produce any ions.

Compound	Melting Point (K)	Boiling Point (K)
Acetic acid (CH3COOH)	290	391
Chloroform (CHCl3)	209	334
Ethanol (CH3CH2OH)	156	351
Methane (CH4)	90	111

Why Carbon Doesn't Form Ions

Carbon has 4 electrons in its outermost shell (atomic number 6) and needs to gain or lose 4 electrons for a noble gas configuration.

• Gaining 4 electrons (C⁴⁻): difficult, since a nucleus with only 6 protons would struggle to hold 10 electrons.
• Losing 4 electrons (C⁴⁺): would need a huge amount of energy.

Molecule	Shared Pairs	Bond Type
H2	1	Single bond
Cl2	1	Single bond
O2	2	Double bond
N2	3	Triple bond
CH4	4 (one per C–H bond)	Four single bonds

Allotrope	Structure	Property
Diamond	Each C bonded to 4 other C atoms, rigid 3D structure	Hardest natural substance known
Graphite	Each C bonded to 3 others in a plane; hexagonal layers	Smooth, slippery, conducts electricity
Fullerene (C-60)	Carbon atoms arranged like a football	Named after architect Buckminster Fuller

Millions of carbon compounds are known — far more than all other elements combined. Two properties explain this:

1. Catenation

Carbon's unique ability to form bonds with other carbon atoms, creating long chains, branched chains or rings. No other element shows catenation to this extent — silicon forms chains of only 7-8 atoms, and these are very reactive, unlike carbon's strong, stable C–C bonds.

2. Tetravalency

Carbon has a valency of four, so it can bond with four other carbon atoms or atoms of other monovalent elements (hydrogen, oxygen, nitrogen, sulphur, chlorine, etc.), forming compounds with a huge range of specific properties.

Compound	Formula	Type
Ethane	C2H6	Saturated (single bond)
Ethene	C2H4	Unsaturated (double bond)
Ethyne	C2H2	Unsaturated (triple bond)

No. of C atoms	Name	Formula
1	Methane	CH4
2	Ethane	C2H6
3	Propane	C3H8
4	Butane	C4H10
5	Pentane	C5H12
6	Hexane	C6H14

Structural Isomers

Butane (C₄H₁₀) can exist as two different structures — a straight chain, or a branched chain — with the same molecular formula. Such compounds are called structural isomers.

Rings and Hydrocarbon Classification

Carbon atoms can also form rings, as in cyclohexane (C₆H₁₂) and benzene (C₆H₆). Compounds containing only carbon and hydrogen are called hydrocarbons:

A heteroatom (or group) that replaces a hydrogen in a hydrocarbon chain, and which gives the compound its characteristic properties, is called a functional group.

Hetero atom	Class of compound	Functional group
Cl/Br	Halo-alkane	—Cl, —Br
Oxygen	Alcohol	—OH
Oxygen	Aldehyde	—CHO
Oxygen	Ketone	—CO— (>C=O)
Oxygen	Carboxylic acid	—COOH

A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain of varying length is called a homologous series — for example, methanol, ethanol, propanol and butanol.

Class	Prefix/Suffix	Example (3-C chain)
Halo alkane	Prefix: chloro-, bromo-	Chloropropane
Alcohol	Suffix: -ol	Propanol
Aldehyde	Suffix: -al	Propanal
Ketone	Suffix: -one	Propanone
Carboxylic acid	Suffix: -oic acid	Propanoic acid
Alkene	Suffix: -ene	Propene
Alkyne	Suffix: -yne	Propyne

• Saturated hydrocarbons generally burn with a clean flame.
• Unsaturated compounds burn with a yellow, sooty flame with lots of black smoke.
• Limiting the air supply causes incomplete combustion and a sooty flame, even for saturated hydrocarbons — seen as blackened cooking vessels when a stove's air holes are blocked.
• Coal and petroleum contain nitrogen and sulphur, whose combustion forms polluting oxides.

Substances capable of adding oxygen to others are called oxidising agents. Alkaline potassium permanganate or acidified potassium dichromate oxidise alcohols to carboxylic acids.

Unsaturated hydrocarbons add hydrogen in the presence of a catalyst (palladium or nickel) to give saturated hydrocarbons. A catalyst speeds up a reaction without being permanently changed itself.

Saturated hydrocarbons are fairly unreactive. But in sunlight, chlorine replaces hydrogen atoms one by one in a fast reaction — this is called a substitution reaction.

Ethanol (commonly called alcohol) is a liquid at room temperature, soluble in water in all proportions, and used as a solvent in medicines like tincture iodine and cough syrups. Pure ethanol (absolute alcohol) is called and even a small quantity can be lethal.

Reactions of Ethanol

Reaction with sodium evolves hydrogen gas and forms sodium ethoxide. Heating with excess concentrated sulphuric acid dehydrates ethanol to ethene (sulphuric acid acts as a dehydrating agent).

Ethanoic acid (acetic acid) belongs to the carboxylic acid group. A 5-8% solution in water is called vinegar. Pure ethanoic acid freezes at 290 K in cold climates, giving it the name glacial acetic acid. Unlike mineral acids like HCl, carboxylic acids are weak acids — not completely ionised.

Reactions of Ethanoic Acid

Reaction with a base gives sodium ethanoate (sodium acetate) and water. Reaction with carbonates/hydrogencarbonates gives a salt, water and carbon dioxide (confirmed by turning lime water milky).

Esterification

An acid catalyst helps ethanoic acid react with ethanol to form a sweet-smelling ester and water — this is used in perfumes and flavouring agents.

Saponification

Treating an ester with sodium hydroxide converts it back to alcohol and the sodium salt of the carboxylic acid — this reaction is called saponification, because it is used to prepare soap.

A soap molecule has two ends with different properties:

• Ionic end — hydrophilic, interacts with water.
• Hydrocarbon (carbon-chain) end — hydrophobic, interacts with oil/grease.

The micelle traps dirt in its centre and stays suspended in water (as a colloid), allowing it to be rinsed away. Soap micelles are large enough to scatter light, which is why a soap solution looks cloudy.

1. What is a covalent bond? Explain with the example of a hydrogen molecule.
2. Why does carbon form covalent compounds instead of ionic ones?
3. What are allotropes? Compare the structures of diamond and graphite.
4. What are the two properties of carbon that lead to the huge number of carbon compounds?
5. What is catenation? Why doesn't silicon show it to the same extent as carbon?
6. Differentiate between saturated and unsaturated carbon compounds, with examples.
7. What are structural isomers? Illustrate with butane.
8. What is a functional group? List any three functional groups with their formulae.
9. What is a homologous series? Explain with an example.
10. Name the compounds represented by (i) a 3-carbon chain with a double bond (ii) a 3-carbon chain with the -OH group.
11. Write balanced equations for the combustion of methane and ethanol.
12. What are oxidising agents? Give an example of an oxidation reaction of ethanol.
13. What is hydrogenation? What is its industrial application?
14. Give a test to differentiate between saturated and unsaturated hydrocarbons.
15. What is a substitution reaction? Give an example involving methane.
16. How would you distinguish experimentally between an alcohol and a carboxylic acid?
17. What is esterification? What is saponification?
18. Explain the mechanism of the cleaning action of soaps.
19. Why do soaps not work well in hard water, but detergents do?
20. Explain why carbon and its compounds are used as fuels for most applications.

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Class 10 Science — Chapter 4

Carbon and its Compounds

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