💎 Carbon and Its Compounds – Full Breakdown

AMU Class 11 Science Chemistry June 2026

        Carbon is the MOST asked chapter in AMU Chemistry after atomic structure. Covalent bonding, allotropes of carbon, homologous series, functional groups, ethanol, ethanoic acid, soaps and detergents — these are the key topics. AMU loves asking about "how many covalent bonds can carbon form," "which allotrope of carbon is hardest," and the cleansing action of soap. This is a high-weightage chapter — let's lock it in.
    

1) Why Carbon is Special — The Unique Properties

Catenation: Carbon can bond with itself to form long chains, branched chains, and rings. This is UNIQUE.
Tetravalency: Carbon has 4 valence electrons → forms 4 covalent bonds.
Small size: Allows strong bonds and multiple bonds (double/triple).

⚠️ AMU Direct: "How many covalent bonds can a carbon atom form?" → 4. "Why does carbon form strong bonds?" → Small size + tetravalency. "What is catenation?" → Self-linking of atoms to form chains.

2) Covalent Bonding in Carbon

Carbon shares electrons (not transfers them like ionic compounds).

Bond Type	Electrons Shared	Example
Single bond (C–C)	1 pair (2 e⁻)	Ethane (C₂H₆), Methane (CH₄)
Double bond (C=C)	2 pairs (4 e⁻)	Ethene (C₂H₄)
Triple bond (C≡C)	3 pairs (6 e⁻)	Ethyne / Acetylene (C₂H₂)

Properties of Covalent Compounds: Low melting/boiling points, poor conductors of electricity, insoluble in water (soluble in organic solvents).

3) Allotropes of Carbon — AMU Favourite

Different physical forms of the same element (carbon) with different arrangements.

Allotrope	Structure	Property	Use
Diamond	Tetrahedral — each C bonded to 4 others	Hardest known natural substance, non-conductor	Cutting tools, jewellery
Graphite	Layered — each C bonded to 3 others	Soft, black, good conductor (1 free e⁻ per C)	Electrodes, lubricant, pencil lead
Fullerene (C₆₀)	Football-shaped (60 C atoms)	Spherical cage-like structure	Drug delivery, nanotechnology
Carbon nanotubes	Rolled graphite sheets	Very strong, conductive	Electronics, composites

⚠️ AMU Gold: "Which is the hardest naturally occurring substance?" → Diamond. "Which allotrope of carbon is a good conductor of electricity?" → Graphite (has free electrons). "Why is graphite used as a lubricant?" → Layers slide over each other easily.

4) Organic Compounds — Hydrocarbons

Compounds containing ONLY carbon and hydrogen.

Saturated vs Unsaturated

	Saturated	Unsaturated
Bonds	Single bonds only (C–C)	Double (C=C) or Triple (C≡C)
Type	Alkanes	Alkenes, Alkynes
General formula	CₙH₂ₙ₊₂	CₙH₂ₙ (alkenes), CₙH₂ₙ₋₂ (alkynes)
Reaction type	Substitution (less reactive)	Addition (more reactive)

Homologous Series

A series of compounds with the same functional group, same general formula, and each member differs by –CH₂–.

Alkane	Formula	Alkene	Formula	Alkyne	Formula
Methane	CH₄	Ethene	C₂H₄	Ethyne	C₂H₂
Ethane	C₂H₆	Propene	C₃H₆	Propyne	C₃H₄
Propane	C₃H₈	Butene	C₄H₈	Butyne	C₄H₆
Butane	C₄H₁₀	Pentene	C₅H₁₀	Pentyne	C₅H₈
Pentane	C₅H₁₂	and so on...

5) Functional Groups

Group	Formula	Suffix/Prefix	Example
Alcohol	–OH	-ol	CH₃OH (Methanol), C₂H₅OH (Ethanol)
Aldehyde	–CHO	-al	HCHO (Formaldehyde), CH₃CHO (Acetaldehyde)
Ketone	–CO–	-one	CH₃COCH₃ (Acetone/Propanone)
Carboxylic Acid	–COOH	-oic acid	CH₃COOH (Ethanoic/Acetic acid)
Halogen	–X (Cl, Br, etc.)	Halo-	CH₃Cl (Chloromethane)
Amine	–NH₂	-amine	CH₃NH₂ (Methylamine)

6) Ethanol & Ethanoic Acid — The Star Compounds

Ethanol (C₂H₅OH)

Preparation: C₂H₅OH + O₂ (yeast / fermentation) — enzyme catalysed
Properties: Colourless liquid, good solvent, burns with blue flame
Reaction with Na: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑ (sodium ethoxide + H₂)
Dehydration: C₂H₅OH → C₂H₄ + H₂O (with conc. H₂SO₄, 443K)
Oxidation: C₂H₅OH → CH₃COOH (with alkaline KMnO₄ or acidified K₂Cr₂O₇)

⚠️ AMU Classic: "What happens when ethanol reacts with sodium?" → Hydrogen gas is released. "What is the product of oxidation of ethanol?" → Ethanoic acid (acetic acid). "Denatured alcohol" → Ethanol + methanol/pyridine (made unfit for drinking).

Ethanoic Acid (CH₃COOH)

Vinegar = 5-8% solution of ethanoic acid in water.
Melting point: 290K (forms ice-like crystals → glacial acetic acid).
Reaction with carbonates: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
Esterification: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O (ester + water)

🧠 Ester trick: The smell of esters is fruity (used in perfumes, flavouring). Esterification = carboxylic acid + alcohol → ester + water. This reaction is reversible.

7) Soaps & Detergents — Cleansing Action

Soap

Made by: Fat/Oil + NaOH → Soap + Glycerol (Saponification reaction)

Structure: RCOONa — ionic head (polar, hydrophilic — water-loving) + long carbon chain tail (non-polar, hydrophobic — water-hating, oil-loving).

Cleansing Action

Tail dissolves in dirt/oil (hydrophobic), head remains in water (hydrophilic). Forms micelles (spherical structures with dirt trapped inside) → rinsed away with water.

⚠️ AMU Question: "Why doesn't soap work well in hard water?" → Hard water has Ca²⁺/Mg²⁺ which react with soap to form scum (insoluble precipitate). Detergents don't form scum — they work better in hard water.

8) Common AMU-Style MCQs

Q1:

How many carbon atoms are there in a molecule of fullerene (C₆₀)?

(a) 50 (b) 60 (c) 70 (d) 80

Answer: (b) 60

Q2:

The general formula of alkanes is:

(a) CₙH₂ₙ (b) CₙH₂ₙ₊₂ (c) CₙH₂ₙ₋₂ (d) CₙHₙ

Answer: (b) CₙH₂ₙ₊₂

Q3:

Which gas is produced when ethanol reacts with sodium?

(a) O₂ (b) CO₂ (c) H₂ (d) N₂

Answer: (c) H₂

Q4:

Vinegar is a solution of ___ in water.

(a) Methanol (b) Ethanol (c) Ethanoic acid (d) Methanoic acid

Answer: (c) Ethanoic acid (5-8%)

Q5:

Which of the following is an unsaturated hydrocarbon?

(a) C₂H₆ (b) C₃H₈ (c) C₂H₄ (d) CH₄

Answer: (c) C₂H₄ (Ethene — alkene with double bond)

9) Quick Revision

Carbon has 4 valence e⁻ → forms 4 covalent bonds. Catenation = self-linking.
Allotropes: Diamond (hardest, non-conductor), Graphite (soft, conductor), Fullerene (C₆₀).
Alkanes: CₙH₂ₙ₊₂, substitution reactions. Alkenes: CₙH₂ₙ, addition reactions.
Ethanol → Ethanoic acid (oxidation with KMnO₄/K₂Cr₂O₇).
Esterification: Acid + Alcohol → Ester + H₂O (fruity smell).
Saponification: Fat + NaOH → Soap + Glycerol.
Soap: ionic head (water-loving) + tail (oil-loving) → forms micelles.
Hard water + soap → scum. Detergents don't form scum.

🧠 Final tip: For AMU, focus on: (1) Allotropes of carbon — diamond vs graphite (2) Homologous series formulas (3) Ethanol properties — especially reaction with Na and oxidation (4) Soap micelle formation. These 4 topics cover 80% of AMU questions from this chapter.