1) Match the pairs

2) Electron-dot structures (without circles)

a) Methane (CH₄)

        H
        |
    H — C — H
        |
        H
    (Each C–H bond = shared pair of electrons ••)
    

b) Ethene (C₂H₄)

    H   H
     \ /
      C = C
     / \
    H   H
    (C=C has two shared pairs)
    

c) Methanol (CH₃OH)

        H
        |
    H — C — O — H
        |
        H
    (O also has two lone pairs •• •• not shown here for simplicity)
    

d) Water (H₂O)

        ..
    H — O — H
        ..
    (Two lone pairs on O shown as "..")
    

3) All possible structural formulae

a) C₃H₈ (Propane)

CH3 — CH2 — CH3

b) C₄H₁₀ (Butane isomers)

n-Butane:        CH3 — CH2 — CH2 — CH3
Isobutane (2-methylpropane): 
                  CH3
                   |
              CH3 — C — H
                   |
                  CH3
    

c) C₃H₄ (Major acyclic isomers)

Propyne (methylacetylene):     CH3 — C ≡ CH
Propadiene (allene):           CH2 = C = CH2
    

4) Short notes / definitions with examples

• a) Structural isomerism: Same molecular formula, different structural formulae. Example: C₄H₁₀ → n-butane & isobutane.
• b) Covalent bond: Bond formed by sharing of electron pairs. Example: O–H in water, C–H in methane.
• c) Hetero atom: Any atom other than C/H in an organic molecule. Example: O in ethanol (CH₃CH₂OH).
• d) Functional group: Specific atom/group imparting characteristic reactions. Example: –OH (alcohol) in ethanol.
• e) Alkane: Saturated hydrocarbon, general formula \( \mathrm{C_nH_{2n+2}} \). Example: propane (C₃H₈).
• f) Unsaturated hydrocarbon: Contains C=C and/or C≡C. Example: ethene (C₂H₄), ethyne (C₂H₂).
• g) Homopolymer: Polymer from a single monomer. Example: Polyethylene from ethene.
• h) Monomer: Small unit that repeats to form a polymer. Example: Styrene → polystyrene.
• i) Reduction: Gain of e⁻/H or loss of O. Example: \( \mathrm{C_2H_4 + H_2 \xrightarrow{Ni} C_2H_6} \) (hydrogenation).
• j) Oxidant (oxidising agent): Substance that causes oxidation (accepts e⁻). Example: Alkaline \( \mathrm{KMnO_4} \) oxidises ethanol to ethanoic acid.

Use Your Brain Power

1) Write the homopolymer structures from the given monomers

2) Polyvinyl acetate → find the monomer

5) IUPAC names

1. a) CH₃–CH₂–CH₂–CH₃ → butane
2. b) CH₃–CHOH–CH₃ → propan-2-ol
3. c) CH₃–CH₂–COOH → propanoic acid
4. d) CH₃–CH₂–NH₂ → ethanamine
5. e) CH₃–CHO → ethanal
6. f) CH₃–CO–CH₂–CH₃ → butan-2-one (butanone)

6) Identify the reaction type

1. a) CH₃–CH₂–CH₂–OH ⟶ CH₃–CH₂–COOH → Oxidation (alcohol → acid)
2. b) CH₃–CH₂–CH₃ ⟶ 3CO₂ + 4H₂O → Complete combustion
3. c) CH₃–CH=CH–CH₃ + Br₂ ⟶ CH₃–CHBr–CHBr–CH₃ → Addition (halogenation)
4. d) CH₃–CH₃ + Cl₂ ⟶ CH₃–CH₂–Cl + HCl → Substitution (free-radical chlorination)
5. e) CH₃–CH₂–CH₂–CH₂–OH ⟶ CH₃–CH₂–CH=CH₂ + H₂O → Elimination / Dehydration
6. f) CH₃–CH₂–COOH + NaOH ⟶ CH₃–CH₂–COO⁻Na⁺ + H₂O → Neutralisation (salt formation)
7. g) CH₃–COOH + CH₃–OH ⟶ CH₃–COO–CH₃ + H₂O → Esterification (condensation)

7) Draw structural formulae for these IUPAC names

8) Answer in brief

1. a) Why so many carbon compounds? Due to catenation (C–C chains/rings), tetravalency, ability to form single/double/triple bonds, strong bonds with many hetero atoms (O, N, S, halogens), and isomerism.
2. b) Types of saturated hydrocarbons (with one example each)
   • Straight-chain alkanes: e.g., propane (CH₃–CH₂–CH₃).
   • Branched-chain alkanes: e.g., isobutane (2-methylpropane).
   • Cycloalkanes: e.g., cyclohexane (C₆H₁₂).
3. c) Any four O-containing functional groups (name, formula & example)
   • Alcohol –OH: ethanol, CH₃CH₂OH
   • Aldehyde –CHO: ethanal, CH₃CHO
   • Ketone >C=O: propanone, CH₃COCH₃
   • Carboxylic acid –COOH: ethanoic acid, CH₃COOH
   • (Also valid: Ether –O–, e.g., CH₃–O–CH₃; Ester –COO–, e.g., CH₃COOCH₂CH₃)
4. d) Three functional groups with different hetero atoms (name, formula & example)
   • Halide (Cl/Br/I): –Cl; chloroethane, CH₃CH₂Cl
   • Amine (N): –NH₂; ethanamine, CH₃CH₂NH₂
   • Nitrile (N): –C≡N; propanenitrile, CH₃CH₂–C≡N
5. e) Three natural polymers: occurrence & monomers

   Polymer	Place of occurrence	Monomer(s)
   Starch	Seeds/tubers (plants)	Glucose (α-D-glucose units)
   Cellulose	Wood; plant cell walls	Glucose (β-D-glucose units)
   Proteins	Muscles, enzymes, skin, etc.	α-Amino acids

6. f) What are vinegar and gasohol? Uses.
   • Vinegar: 5–8% aqueous solution of ethanoic (acetic) acid. Uses: food preservative, flavouring, cleaning.
   • Gasohol: Petrol blended with ethanol (alcohol). Uses: cleaner fuel; improves combustion; reduces emissions.
7. g) What is a catalyst? One catalysed reaction.
   A catalyst changes the rate of a reaction without being consumed.
   Example (hydrogenation): \( \mathrm{R{-}CH{=}CH{-}R' + H_2 \xrightarrow{Ni/Pt} R{-}CH_2{-}CH_2{-}R'} \) Ni/Pt catalyst
   (Vegetable oil → vanaspati ghee)