Grade 10 ||Hydrocarbons and Their Compounds|| Notes

1. Introduction

Compounds are substances made of two or more elements chemically combined.

Compounds are classified into:

• Inorganic (non-carbonic) compounds – obtained from minerals (e.g., salts, oxides).
• Organic (carbonic) compounds – obtained from plants and animals.
• Note: All compounds of carbon except CO, CO₂, carbonates, bicarbonates, and carbides are organic compounds.
• Hydrocarbons are carbonic compounds that contain only carbon (C) and hydrogen (H).
• Examples of hydrocarbons: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈).
• Sources of hydrocarbons: Petroleum, natural gas, coal, and plant/animal sources.

2. Organic Compounds

Organic compounds consist mainly of carbon, hydrogen, and sometimes oxygen, nitrogen, halogens, sulfur, or phosphorus.

• They are covalently bonded compounds.
• Examples: Methane, Ethane, Ethene, Acetylene, Methanol, Proteins, Oils.
• Branch of chemistry that studies these compounds: Organic Chemistry or Carbon Chemistry.

Combustibility:

• Combustible substances (e.g., wood, kerosene) → Organic
• Non-combustible substances (e.g., glass, stone) → Inorganic

3. Hydrocarbons

Composed only of carbon and hydrogen.

Main source: Petroleum.

Types based on carbon-carbon bonds:

Saturated hydrocarbons (Alkanes) – single bonds only

Unsaturated hydrocarbons – double or triple bonds

3.1 Saturated Hydrocarbons (Alkanes)

Definition:
Hydrocarbons in which all carbon-carbon bonds are single bonds.

Also called paraffins.

Stable and less reactive compared to unsaturated hydrocarbons.

General formula: CₙH₂ₙ₊₂

Examples of Alkanes

Key Points:

Saturated → cannot add more hydrogen.

Reactivity: Low → undergo combustion and substitution reactions.

Physical state: Methane, ethane, propane → gases; higher alkanes → liquids/solids.

C–C–C–C–H

3.2 Unsaturated Hydrocarbons

Definition:
Hydrocarbons that have double or triple bonds between carbon atoms.

Less stable and highly reactive.

Often called olefins.

(a) Alkene – Double Bond Hydrocarbons

General formula: CₙH₂ₙ

Properties: Unsaturated, reactive, undergo addition reactions.

(b) Alkyne – Triple Bond Hydrocarbons

General formula: CₙH₂ₙ₋₂

Properties: Highly unsaturated, very reactive, undergo addition and combustion reactions.

Key Points:

Alkenes: Double bonds → addition reactions (e.g., hydrogenation).

Alkynes: Triple bonds → more reactive than alkenes.

Both are unsaturated → can form more bonds with hydrogen.

4. Differences between Saturated and Unsaturated Hydrocarbons

5. Homologous Series

• Definition: Series of hydrocarbons with similar structure, chemical properties, and the same general formula.
• Each member differs by CH₂ unit from the next.
• Example: Methane → Ethane → Propane → Butane
• Molecular weight difference between successive members: 14

6. Alkyl Radical

• Definition: A group formed by removing one hydrogen from an alkane molecule.
• General formula: CₙH₂ₙ₊₁
• Example: –CH₃, –C₂H₅

7. Functional Groups

Definition: Atom or group of atoms that determines the chemical reactivity of an organic compound.

Examples:

• Hydroxyl group: –OH (alcohols)
• Carbonyl group: –CHO (aldehydes)
• Carboxyl group: –COOH (acids)

8. Nomenclature of Hydrocarbons (IUPAC System)

Step 1: Find the root based on number of carbon atoms:

Step 2: Add suffix based on bond type:

Step 3: Combine Root + Suffix

Example: C₂H₆ → Ethane (2 carbons + single bond → -ane)

Example: C₃H₆ → Propene (3 carbons + double bond → -ene)

Example: C₄H₆ → Butyne (4 carbons + triple bond → -yne)

Key Points:

• Number carbon atoms from the end closest to the double/triple bond.
• For multiple double/triple bonds, use di-, tri-, etc. (e.g., Butadiene, Pentayne).
• Side chains/branches are named as alkyl groups (methyl-, ethyl-, propyl-, etc.) and their position is indicated by number.

9. Important Hydrocarbons and Their Uses

Methane (CH₄)

• Source: Marshy areas, biogas, sewage gas
• Properties: Colorless, odorless, tasteless, insoluble in water
• Uses:
• Cooking fuel (biogas)
• Making carbon black for ink, paint, polish
• Preparation of chloroform, carbon tetrachloride, methanol

Ethane (C₂H₆)

Found in natural gas, petroleum

Uses:

• Heat source in welding
• Making ethyl chloride, nitroethane

Propane (C₃H₈)

• Found in natural gas
• Uses: Fuel, coolant, raw material for carbon compounds

Butane (C₄H₁₀)

• Found in petroleum
• Uses: LPG fuel, synthetic rubber

10. Alcohols

1. Compounds derived from alkanes by replacing H with –OH group
2. General formula: CₙH₂ₙ₊₁OH
3. Functional group: Hydroxyl (–OH)

Types:

1. Monohydric (1 –OH) → Methanol, Ethanol
2. Dihydric (2 –OH) → Glycol (e.g., Ethane-1,2-diol)
3. Trihydric (3 –OH) → Glycerol

Uses

1. Methanol: Solvent, formaldehyde, fuels
2. Ethanol: Drinks, antiseptics, lab preservative, manufacturing
3. Glycol: Coolants, antifreeze
4. Glycerol: Soap, cosmetics, sweetening, skin protection

11. Hydrogenation

Process of converting unsaturated fatty acids to saturated fatty acids by adding hydrogen (H₂).

Example: Vegetable oil → Vanaspati ghee

12. Summary

1. Hydrocarbons: Only C and H, found in petroleum, natural gas
2. Saturated: Single bond, stable, alkanes
3. Unsaturated: Double/triple bonds, reactive, alkenes/alkynes
4. Organic compounds: Contain C, covalently bonded, derived from plants/animals
5. Functional groups define reactivity and type of organic compound
6. IUPAC nomenclature gives systematic names