9.1 Saturated and Unsaturated Hydrocarbons

Introduction

Hydrocarbons are organic compounds composed solely of carbon (C) and hydrogen (H). Carbon atoms attach to each other to form the backbone of the compound. Hydrogen atoms attach to the carbon atoms in a variety of ways.

Hydrocarbons make up the major component of petroleum and natural gas (methane). They are raw materials for plastics, fibers, explosives, and many industrial chemicals.

Hydrocarbons are classified into two main types based on the types of bonds between carbon atoms:

• Saturated hydrocarbons — contain only single bonds.
• Unsaturated hydrocarbons — contain at least one multiple bond (double or triple).

This section explains the difference between saturated and unsaturated hydrocarbons.

Definition

Hydrocarbons: Hydrocarbons are compounds containing carbon and hydrogen only.

Saturated Hydrocarbons: Hydrocarbons whose carbon-carbon bonds are all single bonds are called saturated.

Unsaturated Hydrocarbons: Hydrocarbons containing carbon-carbon multiple bonds are called unsaturated.

In simple words:

• Saturated = only single bonds.
• Unsaturated = at least one double or triple bond.

Main Idea

• Hydrocarbons are compounds containing only carbon and hydrogen.
• Saturated hydrocarbons contain only single bonds between carbon atoms.
• They are also called alkanes.
• Their general formula is C_nH_2n+2.
• Unsaturated hydrocarbons contain at least one multiple bond (double or triple).
• They are further divided into:
• Alkenes — contain at least one carbon-carbon double bond.
• Alkynes — contain at least one carbon-carbon triple bond.
• Alkenes have the general formula C_nH_2n.
• Alkynes have the general formula C_nH_2n-2.

Core Concept

Key point: Saturated hydrocarbons have only single bonds; unsaturated hydrocarbons have at least one double or triple bond.

Detailed Explanation

What are Hydrocarbons?

Hydrocarbons are organic compounds composed solely of carbon (C) and hydrogen (H).

• Carbon atoms attach to each other to form the backbone of the compound.
• Hydrogen atoms attach to the carbon atoms in a variety of ways.
• Hydrocarbons make up the major component of petroleum and natural gas (methane).
• They are raw materials for plastics, fibers, explosives, and many industrial chemicals.

Key point: Hydrocarbons contain only carbon and hydrogen.

Saturated Hydrocarbons

Definition: Hydrocarbons whose carbon-carbon bonds are all single bonds are called saturated.

Key features:

• Saturated hydrocarbons are also called alkanes.
• In alkanes, each carbon atom is bonded to four other atoms.
• Methane is the simplest alkane.
• Other examples are ethane, propane, butane, etc.
• The general formula of alkanes is C_nH_2n+2, where n is the number of carbon atoms.

Examples:

• Methane (CH₄): 1 carbon atom
• Ethane (C₂H₆): 2 carbon atoms
• Propane (C₃H₈): 3 carbon atoms
• Butane (C₄H₁₀): 4 carbon atoms

Key point: Saturated hydrocarbons contain only single bonds and are called alkanes.

Unsaturated Hydrocarbons

Definition: Hydrocarbons containing carbon-carbon multiple bonds are called unsaturated.

Unsaturated hydrocarbons are further divided into:

(i) Alkenes

• Unsaturated hydrocarbons containing at least one carbon-carbon double bond.
• They have the general formula C_nH_2n.
• Example: Ethene (CH₂ = CH₂).

(ii) Alkynes

• Unsaturated hydrocarbons that have at least one carbon-carbon triple bond.
• They have the general formula C_nH_2n-2.
• Example: Ethyne (H - C ≡ C - H).

Key point: Unsaturated hydrocarbons contain at least one double or triple bond.

Examples of Saturated and Unsaturated Hydrocarbons

Key point: The type of hydrocarbon depends on the types of bonds between carbon atoms.

Summary Table

Intermediate Level

Saturated hydrocarbons:

• Contain only single bonds.
• Called alkanes.
• General formula: C_nH_2n+2.
• Each carbon atom is bonded to four other atoms.
• Examples: Methane, Ethane, Propane, Butane.

Unsaturated hydrocarbons:

• Contain at least one multiple bond.
• Divided into:
• Alkenes — at least one double bond; general formula C_nH_2n.
• Alkynes — at least one triple bond; general formula C_nH_2n-2.
• Examples: Ethene (alkene), Ethyne (alkyne).

Key point: The type of hydrocarbon depends on the types of bonds between carbon atoms.

Important Points

• - Hydrocarbons = compounds containing only carbon and hydrogen.
• - Saturated hydrocarbons = only single bonds; also called alkanes.
• - General formula: C_nH_2n+2
• - Examples: Methane, Ethane, Propane, Butane
• - Unsaturated hydrocarbons = at least one multiple bond.
• - Alkenes = at least one double bond; general formula C_nH_2n.
• - Example: Ethene (CH₂ = CH₂)
• - Alkynes = at least one triple bond; general formula C_nH_2n-2.
• - Example: Ethyne (H - C ≡ C - H)
• - Hydrocarbons make up the major component of petroleum and natural gas.
• - They are raw materials for plastics, fibers, explosives, and many industrial chemicals.

Remember

• - Hydrocarbons = carbon + hydrogen only.
• - Saturated = only single bonds = alkanes.
• - Unsaturated = at least one double or triple bond.
• - Alkenes = double bond; general formula C_nH_2n.
• - Alkynes = triple bond; general formula C_nH_2n-2.
• - Examples:
• - Saturated: Methane, Ethane, Propane
• - Unsaturated (alkene): Ethene, Propene
• - Unsaturated (alkyne): Ethyne, Propyne
• - Hydrocarbons are the main components of petroleum and natural gas.

Common Mistakes

Quick Revision

Saturated and Unsaturated Hydrocarbons:

Hydrocarbons are organic compounds composed solely of carbon (C) and hydrogen (H). Carbon atoms attach to each other to form the backbone of the compound. Hydrogen atoms attach to the carbon atoms in a variety of ways. Hydrocarbons make up the major component of petroleum and natural gas (methane). They are raw materials for plastics, fibers, explosives, and many industrial chemicals.

Saturated Hydrocarbons: Hydrocarbons whose carbon-carbon bonds are all single bonds are called saturated. Saturated hydrocarbons are also called alkanes. In alkanes, each carbon atom is bonded to four other atoms. Methane is the simplest alkane. Other examples are ethane, propane, butane, etc. The general formula of alkanes is C_nH_2n+2, where n is the number of carbon atoms.

• Unsaturated Hydrocarbons:
• Hydrocarbons containing carbon-carbon multiple bonds are called unsaturated. Unsaturated hydrocarbons are further divided into:

• (i) Alkenes:
• Unsaturated hydrocarbons containing at least one carbon-carbon double bond are called alkenes. They have the general formula C_nH_2n, for example, ethene.

• (ii) Alkynes:
• Unsaturated hydrocarbons that have at least one carbon-carbon triple bond are called alkynes. They have a general formula C_nH_2n-2, for example, ethyne.

• Concept Assessment Exercise 9.1:
• Choose saturated and unsaturated compounds from the following:
• (i) CH₃-CH₂-CH₃
• (ii) CH₃-C ≡ CH
• (iii) CH₃-CH = CH₂
• (iv) CH₂ = CH - CH = CH₂

• Saturated: (i) CH₃-CH₂-CH₃
• Unsaturated: (ii) CH₃-C ≡ CH, (iii) CH₃-CH = CH₂, (iv) CH₂ = CH - CH = CH₂

60-Second Revision

• Hydrocarbons = carbon + hydrogen only.
• Saturated = only single bonds = alkanes.
• Unsaturated = at least one double or triple bond.
• Alkenes = double bond; general formula C_nH_2n.
• Alkynes = triple bond; general formula C_nH_2n-2.
• Examples:
• Saturated: Methane, Ethane, Propane
• Unsaturated (alkene): Ethene, Propene
• Unsaturated (alkyne): Ethyne, Propyne
• Hydrocarbons are the main components of petroleum and natural gas.
• ⚠️ Warning: saturated hydrocarbons have only single bonds; unsaturated hydrocarbons have at least one double or triple bond.