Chapter 4: Carbon and Its Compounds (notes with previous years questions)

Class 10 Science - Chapter 4: Carbon and Its Compounds

1. Introduction to Carbon

Carbon is the 4^th most abundant element in the universe and the 15^th most abundant element in the Earth's crust.

Atomic number of carbon: 6

Electronic configuration: 2, 4

Carbon achieves stability by sharing electrons, forming covalent bonds.

2. Why Carbon is Unique

1. Catenation: Carbon can form long chains, branched chains, and rings by bonding with other carbon atoms.

Example: Ethane (C₂H₆), Propane (C₃H₈), Benzene (C₆H₆).

2. Tetravalency: Carbon can form 4 covalent bonds with other atoms (e.g., hydrogen, oxygen, nitrogen, etc.).

Example: Methane (CH₄), Carbon tetrachloride (CCl₄).

3. Formation of Multiple Bonds: Carbon can form single (C-C), double (C=C), or triple (C≡C) bonds.

Example: Ethene (C₂H₄), Ethyne (C₂H₂).

3. Allotropes of Carbon

Allotropes are different forms of the same element with different physical properties but the same chemical properties.

Main allotropes of carbon:

1. Diamond:

• Each carbon atom is bonded to four other carbon atoms in a tetrahedral structure.
• Uses: Cutting tools, jewelry, and industrial drills.

2. Graphite:

• Each carbon atom is bonded to three other carbon atoms in hexagonal layers.
• Uses: Lubricant, pencil lead, and electrodes.

3. Fullerenes:

• Spherical or cylindrical molecules.
• Example: Buckminsterfullerene (C₆₀).
• Uses: Nanotechnology, drug delivery, and superconductors.

4. Covalent Bonding in Carbon Compounds

Covalent bond: A bond formed by the sharing of electrons between atoms.

Examples of covalent compounds:

1. Methane (CH₄): Carbon shares 4 electrons with 4 hydrogen atoms.

2. Ethane (C₂H₆): Two carbon atoms share a single bond, and each carbon atom shares electrons with 3 hydrogen atoms.

3. Ethene (C₂H₄): Two carbon atoms share a double bond, and each carbon atom shares electrons with 2 hydrogen atoms.

5. Versatile Nature of Carbon

Carbon forms a large number of compounds due to:

1. Catenation: Ability to form long chains.

2. Tetravalency: Ability to form 4 bonds.

3. Isomerism: Compounds with the same molecular formula but different structural formulas.

Example: Butane (C₄H₁₀) has two isomers: n-butane and isobutane.

6. Hydrocarbons

Hydrocarbons are compounds made up of carbon and hydrogen atoms.

Types of hydrocarbons:

1. Saturated hydrocarbons (Alkanes):

• All carbon-carbon bonds are single bonds.
• General formula: C_nH_2n+2.
• Example: Methane (CH₄), Ethane (C₂H₆).

2. Unsaturated hydrocarbons:

• Contain double or triple bonds between carbon atoms.
• Alkenes: Contain at least one double bond. General formula: C_nH_2n. Example: Ethene (C₂H₄).
• Alkynes: Contain at least one triple bond. General formula: C_nH_2n-2. Example: Ethyne (C₂H₂).

7. Functional Groups

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

Common functional groups:

1. Alcohol (-OH): Example: Ethanol (C₂H₅OH).

2. Aldehyde (-CHO): Example: Ethanal (CH₃CHO).

3. Ketone (-CO-): Example: Propanone (CH₃COCH₃).

4. Carboxylic acid (-COOH): Example: Ethanoic acid (CH₃COOH).

5. Halogen (-X): Example: Chloromethane (CH₃Cl).

8. Homologous Series

A group of organic compounds with the same functional group and similar chemical properties.

Each successive member differs by -CH₂ (methylene group).

Properties of homologous series:

1. Same general formula.

2. Similar chemical properties.

3. Gradual change in physical properties (e.g., boiling point, melting point).

9. Nomenclature of Carbon Compounds

IUPAC rules for naming organic compounds:

1. Identify the longest carbon chain.

2. Number the carbon atoms in the chain.

3. Identify and name the functional group.

4. Use prefixes (e.g., meth-, eth-, prop-) to indicate the number of carbon atoms.

5. Use suffixes (e.g., -ane, -ene, -ol) to indicate the type of compound.

10. Chemical Properties of Carbon Compounds

1. Combustion:

Hydrocarbons burn in the presence of oxygen to produce carbon dioxide, water, and heat.

Example: CH₄ + 2O₂ → CO₂ + 2H₂O + Heat.

2. Oxidation:

Alcohols are oxidized to carboxylic acids in the presence of oxidizing agents.

Example: C₂H₅OH + 2[O] → CH₃COOH + H₂O.

3. Addition Reaction:

Unsaturated hydrocarbons (alkenes and alkynes) undergo addition reactions.

Example: C₂H₄ + H₂ → C₂H₆.

4. Substitution Reaction:

Saturated hydrocarbons (alkanes) undergo substitution reactions.

Example: CH₄ + Cl₂ → CH₃Cl + HCl.

11. Important Carbon Compounds

1. Ethanol (C₂H₅OH):

• Used as a solvent, in alcoholic beverages, and as a fuel.
• Produced by the fermentation of sugars.

2. Ethanoic Acid (CH₃COOH):

• Commonly known as acetic acid.
• Used in vinegar and as a preservative.

12. Soaps and Detergents

Soap:

• Made by the saponification of fats/oils with sodium hydroxide.
• Structure: Hydrophobic tail (non-polar) and hydrophilic head (polar).
• Cleans by forming micelles that trap dirt and oil.

Detergents:

• Synthetic cleaning agents.
• Work in both hard and soft water.

13. Differences Between Soaps and Detergents

Property	Soap	Detergent
Source	Natural (fats/oils)	Synthetic
Effect in hard water	Forms scum (insoluble precipitate)	No scum (works well in hard water)
Biodegradability	Biodegradable	Some are non-biodegradable

14. Previous Year Questions with Answers

Question 1: What is the difference between saturated and unsaturated hydrocarbons?

Answer: Saturated hydrocarbons contain only single bonds between carbon atoms (e.g., alkanes like C_nH_2n+2). Unsaturated hydrocarbons contain double or triple bonds (e.g., alkenes like C_nH_2n and alkynes like C_nH_2n-2).

Question 2: What is a homologous series? Give an example.

Answer: A homologous series is a group of organic compounds with the same functional group and similar chemical properties. Example: Alkanes (C_nH_2n+2) like Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈).

Question 3: Why does carbon form a large number of compounds?

Answer: Carbon forms a large number of compounds due to catenation, tetravalency, and isomerism.

Question 4: What is the role of soap in cleaning?

Answer: Soap molecules have a hydrophobic tail and a hydrophilic head. They form micelles that trap dirt and oil, allowing them to be washed away with water.