ICSE Class 10 Chemistry: Introduction to Hydrocarbons

Introduction to Hydrocarbons

Ever wondered why gasoline powers your bike? The secret lies in tiny carbon‑hydrogen chains called hydrocarbons.

💡 In Simple Words: Hydrocarbons are molecules made only of carbon and hydrogen atoms. They can be as simple as methane (one carbon) or as long as the wax on a candle. All the fuels we use, like petrol and natural gas, belong to this family.

What is a Hydrocarbon?

A hydrocarbon is any organic compound that contains only carbon (C) and hydrogen (H) atoms. No oxygen, nitrogen or other elements are present. Think of it like a LEGO train: the carbon pieces are the sturdy cars and the hydrogen pieces are the tiny connectors that link them together.

Why Do Hydrocarbons Matter in ICSE Chemistry?

• They form the foundation of the organic chemistry syllabus.
• All major fuels (petrol, diesel, natural gas) are hydrocarbons, so they connect classroom theory to everyday life.
• Understanding their structure helps you grasp concepts like isomerism and reactions later on.

Classification of Hydrocarbons

Hydrocarbons fall into two big families based on the type of bonds between carbon atoms.

• Saturated hydrocarbons – every carbon‑carbon link is a single bond. No extra hydrogen can be added without breaking a bond. These are called alkanes.
• Unsaturated hydrocarbons – at least one carbon‑carbon link is a double or triple bond, so they can “take in” more hydrogen. These are split into alkenes (double bond) and alkynes (triple bond).

General Properties

• They are mostly non‑polar, so they don’t mix well with water but dissolve in oils.
• Low boiling points for short chains (e.g., methane boils at –161°C) and higher for long chains.
• Combustion (burning) releases energy, carbon dioxide and water – the basis of most fuels.

Simple Examples

Methane (CH4) – the simplest alkane, used as household gas.

Ethene (C2H4) – a key alkene; it’s the building block for making plastics.

Acetylene (C2H2) – an alkynes famous for welding torches.

Comparison of Alkanes, Alkenes & Alkynes

Quick Summary

• Hydrocarbons = only C and H.
• Alkanes: single bonds, formula CnH2n+2 (saturated).
• Alkenes: at least one double bond, formula CnH2n (unsaturated).
• Alkynes: at least one triple bond, formula CnH2n-2 (unsaturated).
• Properties: non‑polar, combustible, low solubility in water.

📝 Likely Exam Questions

1. Define a hydrocarbon and give two examples.
   Answer: A hydrocarbon is an organic compound containing only carbon and hydrogen atoms. Examples: methane (CH4) and ethene (C2H4).
2. Write the general formulas for alkanes, alkenes and alkynes.
   Answer: Alkanes – CnH2n+2; Alkenes – CnH2n; Alkynes – CnH2n-2.
3. Explain why hydrocarbons are poor solvents for salts.
   Answer: Hydrocarbons are non‑polar, meaning they have no significant charge separation. Salts are ionic (charged) and dissolve best in polar solvents like water that can stabilize the ions.
4. List three differences between alkanes and alkenes.
   Answer: (i) Bond type – alkanes have only single bonds; alkenes have at least one double bond. (ii) General formula – CnH2n+2 vs CnH2n. (iii) Reactivity – alkenes undergo addition reactions, alkanes are relatively inert.
5. What is the product when ethene reacts with hydrogen in the presence of a catalyst?
   Answer: Ethane (C2H6) – the double bond is “hydrogenated” to a single bond.