Carbon and Its Compounds – Class 10 Chemistry Chapter 4 NCERT Notes

Chapter 4: Carbon and Its Compounds

4.1 Bonding in Carbon — The Covalent Bond

Carbon has 4 electrons in its outermost shell (electronic configuration: 2, 4). It needs 4 more electrons to complete its octet. Instead of gaining or losing electrons, carbon shares electrons with other atoms, forming covalent bonds.

Types of Covalent Bonds

• Single Bond (–): One pair of electrons shared. Example: CH₄ (methane). Each C–H bond is a single bond.
• Double Bond (=): Two pairs of electrons shared. Example: O₂ (oxygen), C₂H₄ (ethene).
• Triple Bond (≡): Three pairs of electrons shared. Example: N₂ (nitrogen), C₂H₂ (ethyne/acetylene).

4.2 Versatile Nature of Carbon

Two unique properties make carbon special:

1. Catenation: The ability of carbon to form bonds with other carbon atoms, creating long chains, branched chains, and rings.
2. Tetravalency: Carbon has a valency of 4, allowing it to bond with four other atoms simultaneously.

4.3 Hydrocarbons

Compounds made up of only carbon and hydrogen are called hydrocarbons. They are classified as:

Saturated Hydrocarbons (Alkanes)

• Contain only single bonds between carbon atoms.
• General formula: CₙH₂ₙ₊₂
• Examples: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), Butane (C₄H₁₀)

Unsaturated Hydrocarbons

• Alkenes: Contain at least one C=C double bond. General formula: CₙH₂ₙ. Example: Ethene (C₂H₄).
• Alkynes: Contain at least one C≡C triple bond. General formula: CₙH₂ₙ₋₂. Example: Ethyne (C₂H₂).

4.4 Functional Groups

An atom or group of atoms that determines the chemical properties of an organic compound is called a functional group.

4.5 Chemical Properties of Carbon Compounds

1. Combustion

Carbon compounds burn in oxygen (air) to produce CO₂, H₂O, heat, and light.

Saturated hydrocarbons burn with a clean blue flame. Unsaturated hydrocarbons burn with a yellow sooty flame (due to incomplete combustion).

2. Oxidation

Alcohols can be converted to carboxylic acids using oxidising agents like alkaline KMnO₄ or acidified K₂Cr₂O₇.

3. Addition Reaction

Unsaturated hydrocarbons undergo addition reactions where atoms are added across the double or triple bond.

This is how vegetable oils are converted to solid fats (vanaspati ghee).

4. Substitution Reaction

Saturated hydrocarbons undergo substitution reactions where one atom replaces another.

4.6 Ethanol (C₂H₅OH) — Important Properties

• Colourless liquid with a pleasant smell
• Used in alcoholic beverages, as a solvent, and in medicines
• Reacts with sodium: 2Na + 2C₂H₅OH → 2C₂H₅ONa + H₂↑
• Dehydration: On heating with conc. H₂SO₄ at 443 K, ethanol gives ethene (C₂H₄)
• Denatured alcohol: Ethanol made unfit for drinking by adding methanol and pyridine

4.7 Ethanoic Acid (CH₃COOH) — Important Properties

• Also known as acetic acid; 5-8% solution in water is called vinegar
• Pure ethanoic acid has a melting point of 290 K — it freezes in cold weather, hence called glacial acetic acid
• Reacts with NaHCO₃ to form CO₂ gas (used as a test for carboxylic acids)
• Esterification: Reacts with alcohols in the presence of acid catalyst to form esters (sweet-smelling compounds used in perfumes and flavouring)

4.8 Soaps and Detergents

Soaps

Soaps are sodium or potassium salts of long-chain carboxylic acids (fatty acids). Example: Sodium stearate (C₁₇H₃₅COONa).

How Soap Cleans

A soap molecule has two ends:

• Hydrophilic end (water-loving): The ionic –COO⁻Na⁺ part, which dissolves in water.
• Hydrophobic end (water-repelling): The long hydrocarbon chain, which dissolves in oil/grease.

When soap is added to dirty clothes, the hydrophobic tails attach to grease, while the hydrophilic heads remain in water. This forms micelles — spherical clusters that trap the dirt and can be washed away.