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Carbon and its Compounds – Class 10 Science notes, important questions and MCQs

NCERT Class 10 Science, chapter 4. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Carbon forms millions of compounds because it shares electrons (covalent bonds), links to itself in chains and rings (catenation) and has a valency of four.

Bonding and allotropes

Carbon has 4 valence electrons and forms covalent bonds by sharing.
Covalent compounds have low melting points and are poor conductors.
Allotropes: diamond (hardest, non-conductor), graphite (soft, conducts), fullerene C₆₀.

Hydrocarbons and functional groups

Saturated (alkanes, single bonds): CₙH₂ₙ₊₂, e.g. methane CH₄.
Unsaturated: alkenes (double bond, CₙH₂ₙ) and alkynes (triple bond, CₙH₂ₙ₋₂).
Functional groups: –OH alcohol, –CHO aldehyde, >C=O ketone, –COOH carboxylic acid, –Cl/–Br halo.
A homologous series differs by –CH₂– (14 u) between members.

Reactions and important compounds

Combustion, oxidation (ethanol → ethanoic acid), addition (hydrogenation of oils with Ni catalyst), substitution (methane + chlorine in sunlight).
Ethanol + ethanoic acid → ester (sweet smell), with acid catalyst.
Soaps (sodium salts of fatty acids) form micelles that remove oily dirt; detergents work even in hard water.

Key terms

Catenation: carbon atoms linking to each other to form long chains
Isomers: compounds with the same molecular formula but different structures
Homologous series: compounds with the same functional group differing by –CH₂–
Micelle: a cluster of soap molecules with oily dirt trapped inside

Formulas

CH₄ + 2O₂ → CO₂ + 2H₂O + heat
CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O (esterification)
Alkane CₙH₂ₙ₊₂, alkene CₙH₂ₙ, alkyne CₙH₂ₙ₋₂

Important questions with answers

Why does carbon form covalent bonds?2 marks

Carbon has 4 valence electrons. Gaining or losing 4 electrons needs too much energy, so it completes its octet by sharing electrons.

What is a homologous series? Write two characteristics with an example.3 marks

A series of compounds with the same functional group in which successive members differ by –CH₂–. Members have similar chemical properties and show a gradual change in physical properties. Example: methanol, ethanol, propanol.

Explain how soaps clean dirty clothes. Why do soaps not work well in hard water and how are detergents better?5 marks

A soap molecule has a long hydrocarbon tail that dissolves in oil and grease and an ionic head that dissolves in water. In water, soap molecules form micelles with the tails trapping oily dirt at the centre; rinsing washes the micelles away. In hard water, Ca²⁺ and Mg²⁺ ions react with soap to form an insoluble scum, so more soap is wasted. Detergents (sulphonate or ammonium salts) do not form scum with these ions, so they clean well in hard water.

Quick revision

Carbon is tetravalent and shows catenation.
Hydrogenation converts oils to fats (Ni catalyst).
Soaps fail in hard water; detergents do not.

Exam tips

Name with root (meth-, eth-, prop-, but-) + suffix (-ane, -ene, -yne, -ol, -al, -one, -oic acid).
Unsaturated compounds burn with a yellow sooty flame.

Practice MCQs

The valency of carbon is
1. 2
2. 3
3. 4
4. 6
Show answer
Answer: (c) 4. It has 4 valence electrons.
The bond in methane is
1. ionic
2. covalent
3. metallic
4. hydrogen
Show answer
Answer: (b) covalent. Electrons are shared.
Which allotrope of carbon conducts electricity?
1. graphite
2. diamond
3. charcoal only
4. none
Show answer
Answer: (a) graphite. Graphite has free electrons.
The general formula of alkenes is
1. CₙH₂ₙ₊₂
2. CₙH₂ₙ
3. CₙH₂ₙ₋₂
4. CₙHₙ
Show answer
Answer: (b) CₙH₂ₙ. One double bond.
The functional group of ethanoic acid is
1. –OH
2. –CHO
3. –COOH
4. >C=O
Show answer
Answer: (c) –COOH. Carboxylic acid group.
Vegetable oils are converted into fats by
1. oxidation
2. saponification
3. substitution
4. hydrogenation
Show answer
Answer: (d) hydrogenation. Addition of hydrogen with nickel catalyst.
Butane has how many structural isomers?
1. 1
2. 2
3. 3
4. 4
Show answer
Answer: (b) 2. n-butane and isobutane.
Which reaction gives a sweet-smelling compound?
1. ethanol + ethanoic acid (acid catalyst)
2. ethanol + sodium
3. methane + chlorine
4. ethanoic acid + NaOH
Show answer
Answer: (a) ethanol + ethanoic acid (acid catalyst). Esterification forms an ester.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.