Carbon is the backbone of organic chemistry. This chapter explains why carbon forms a vast number of compounds, how to name and classify simple organic molecules, and the common reactions of alcohols, carboxylic acids, and esters. Focus on: tetravalency, covalent bonding, homologous series, isomerism, functional groups (—OH, —COOH, —COOR), physical properties (boiling/melting points, solubility), and key reactions such as esterification and saponification.

Learning Goals

• Understand tetravalency and catenation as reasons for carbon's versatility.
• Identify homologous series and simple structural isomers.
• Name simple alkanes, alkenes, alcohols, and carboxylic acids using IUPAC basics.
• Explain physical and chemical properties of common carbon compounds.
• Solve board-style questions with clear, exam-focused answers.

Tetravalency and Covalent Bonding

Carbon has atomic number 6; its outer shell has four electrons. To attain a stable electronic configuration, carbon forms four covalent bonds. Because of its size and bonding capacity, carbon forms strong C–C bonds and long chains (catenation).

Homologous Series

A homologous series is a family of compounds with the same functional group and successive members differing by a —CH₂— unit. Members show similar chemical properties and a gradual change in physical properties.

Isomerism

Isomers are compounds with the same molecular formula but different structural arrangements. For example, C₄H₁₀ gives n‑butane and isobutane (branched form).

Functional Groups (NCERT Focus)

• Alcohols: —OH (example: ethanol CH₃CH₂OH). Physical property — hydrogen bonding causes higher boiling points.
• Carboxylic acids: —COOH (example: ethanoic acid CH₃COOH). Show acidic behavior and react with alcohols to form esters.
• Esters: —COOR (example: ethyl ethanoate CH₃COOCH₂CH₃). Often have pleasant fruity smells; made by esterification.

Understand the following patterns — these are often tested in short-answer questions:

Combustion

All carbon compounds burn in oxygen to give CO₂ and H₂O (complete combustion) or CO/C (incomplete combustion). E.g., CH₄ + 2O₂ → CO₂ + 2H₂O.

Oxidation of Alcohols

Primary alcohols can be oxidised to form aldehydes and further to carboxylic acids (in presence of strong oxidising agents). Secondary alcohols form ketones; tertiary alcohols resist oxidation under mild conditions.

Esterification (Important)

Acid + Alcohol ⇌ Ester + Water (conc. H₂SO₄ as catalyst). Example:

CH3CH2OH + CH3COOH ⇌ CH3COOCH2CH3 + H2O

Saponification

Hydrolysis of esters (fats/oils) by NaOH gives glycerol and soap (salts of fatty acids). This process explains how soaps are formed from natural fats.

Practice writing the IUPAC names of simple compounds and drawing their structural formulas — this helps in scoring well on 2–3 mark questions.

• CH₄ — Methane
• CH₃CH₃ — Ethane
• CH₂=CH₂ — Ethene
• CH₃CH₂OH — Ethanol
• CH₃COOH — Ethanoic acid

• Define first: Start answers with a clear definition or formula when applicable.
• Use equations: Write balanced chemical equations neatly and label conditions (e.g., catalyst, temperature).
• Diagrams earn marks: Labelled structures, mechanism sketches, or flowcharts add value.
• Short and precise: For 1–2 mark questions give one-sentence definitions or examples; for 3–5 marks give short steps and equations.
• Time management: Practice previous-year questions and allot time per section during revision.

Short Answer (1–2 marks)

1. What is catenation? Ans: Ability of carbon to form chains by bonding with itself. (1 mark)
2. Give one use of esters. Ans: Flavorings and perfumes. (1 mark)

Long Answer (3–5 marks)

1. Explain esterification with an equation and mention the catalyst.
   Answer hint: Write the general reaction Alcohol + Carboxylic acid ⇌ Ester + Water. Mention conc. H₂SO₄ as catalyst. (3 marks)
2. Describe saponification and write a balanced equation.
   Answer hint: Hydrolysis of fat by NaOH gives glycerol and sodium salts of fatty acids (soap). Provide a balanced equation for a simple triglyceride if asked. (4 marks)

MCQ Example

Which functional group is present in ethanoic acid?
A) —OH    B) —COOH    C) —CHO    D) —NH₂
Correct: B