Carbon and Its Compounds Unsaturated Hydrocarbons

These notes are based on the chapter Carbon and its Compounds from class 10 science of NCERT book and CBSE syllabus.

• Alkene: C_nH_2n
• Alkyne: C_nH_{2n − 2}
• Cyclic Hydrocarbon

Alkene: Unsaturated hydrocarbon with at least one double bond between two carbon atoms.

Alkyne: Unsaturated hydrocarbon with at least one triple bond between two carbon atoms.

Cyclic hydrocarbon:When carbon atoms form a ring, instead of chain.

Alkene

Hydrocarbons having at least one double bond between two carbon atoms are known as ALKENE. General formula of alkene is C_nH_2n where n is number of carbon atoms.

If C = 1 then C_nH_2n = C₁H_{2 × 1} = CH₂

Since, hydrocarbon having one carbon atom is known as Methane. Thus, Methane – ane + ene = Methene. But, alkene does not exist with one carbon atom, thus, methene does not exist.

If C = 2 then C_nH_2n = C₂H_{2 × 2} = C₂H₄

Name of this compound is ethane − ane + ene = ethene. This molecule can be shown by following structural formula.

If C = 3 then C_nH_2n = C₃H_{2 × 3} = C₃H₆

Name of this compound is: butane − ane + ene = butene. This molecule can be shown by following structural formula.

Other alkenes are formed in similar way.

Alkyne

Hydrocarbons having at least one triple bond between two carbon atoms are known as alkyne. (Alkane – ane + yne = Alkyne). Similarly,

Ethane – ane + yne = Ethyne
Propane – ane + yne = Propyne
Butane – ane + yne = Butyne
Pentane – ane + yne = Pentyne

General formula of alkyne is C_nH_{2n − 2}. As in case of alkene, minimum two carbon atoms are required to form alkyne.

If C = 2, then, C_nH_{2n − 2} = C₂H_{2 × 2 − 2} = C₂H₂

The name of this compound is ethyne. This can be shown by following structural formula.

If C = 3, then, C_nH_{2n − 2} = C₃H_{2 × 3 − 2} = C₃H₄

The name of this compound is propyne. This can be shown by following structural formula.

If C = 4, then, C_nH_{2n − 2} = C₄H_{2 × 4 − 2} = C₄H₆

The name of this compound is butyne. This can be shown by following structural formula.

Other alkynes are formed in similar way.

Cyclic Hydrocarbon:

Carbon can form cyclic structure combining with carbon atoms. Such hydrocarbons are known as cyclic hydrocarbon. Structural formulae of some of the cyclic hydrocarbons are as follows: