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Saturated and Unsaturated Hydrocarbons

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Carbon compounds are referred to as organic compounds. Most organic compounds contain hydrogen, and many organic compounds contain oxygen or other elements in addition to carbon. As a result, the vast majority of organic compounds are hydrocarbons, which contain only hydrogen and carbon. Let’s talk about hydrocarbons and their various types.

What are Hydrocarbons?

Hydrocarbon is a chemical compound that consists only of hydrogen and carbon. Hydrocarbon is made up of two elements: hydrogen and carbon. 

Since methane (CH4), ethane (C2H6), ethyne (C2H2), and so on are all made up of only two elements: hydrogen and carbon, so these are all hydrocarbons. 

Petroleum, often known as crude oil, is the most important natural source of hydrocarbons. It is extracted from underground oil deposits by drilling oil wells. Hydrocarbons can also be found in natural gas found above petroleum deposits.

Types of Hydrocarbons: Hydrocarbons are of two types which are saturated hydrocarbons and unsaturated hydrocarbons.

Saturated Hydrocarbons

A saturated hydrocarbon is one in which all of the carbon atoms are connected by a single bond. Saturated hydrocarbons are also called alkanes. 

An alkane is a hydrocarbon in which the carbon atoms are only connected together by a single covalent bond. In an alkane, there are no double or triple bonds. As a result, the hydrocarbons methane, ethane, propane, and butane form a series of compounds known as alkanes.  All of these saturated hydrocarbons have ‘ane’ at the end of their names. 

The general formula of saturated hydrocarbons or alkanes is CnH2n+2 where n is the number of carbon atoms in one molecule of the alkane. 

  • If an alkane has 1 carbon atom in its molecules, then n= 1, and its molecular formula will be C1H2(1)+2 or CH4.
  • If an alkane has 2 carbon atoms in its molecule, then n= 2, and its molecular formula will be C2H2(2)+2 or C2H6.
  • If an alkane has 3 carbon atoms in its molecule, then n= 3, and its molecular formula will be C3H2(3)+2 or C3H8.
  • If an alkane has 4 carbon atoms in its molecule, then n= 4, and its molecular formula will be C4H2(4)+2 or C4H10.

Methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H10), are all saturated hydrocarbons which contain only carbon-carbon single bonds are shown below. 

Structural formulae of some alkanes.

Unsaturated Hydrocarbons

An unsaturated hydrocarbon is one in which two carbon atoms are connected by a double bond or triple bond. Two important unsaturated hydrocarbons are ethene (C2H4) and ethyne (C2H2) because ethyne contains a triple bond and ethene contains a double bond between the two carbon atoms. 

A double bond is formed by sharing two pairs of electrons between two carbon atoms whereas, a triple bond is formed by sharing three pairs of electrons between two carbon atoms. 

Unsaturated hydrocarbons are typically obtained from petroleum through a process known as cracking. Unsaturated hydrocarbons are of two types,

  • those containing carbon-carbon double bonds called alkenes and 
  • those containing carbon-carbon triple bonds called alkynes. 

Alkenes 

An alkene is an unsaturated hydrocarbon with two carbon atoms connected together by a double bond. Alkenes have a double bond between two carbon atoms that are formed by sharing two pairs of electrons, resulting in a total of four electrons. 

Since they have a double bond between two carbon atoms, ethene (CH) and propene (CH) are alkenes. Since an alkene has a double bond between two carbon atoms, the molecule of the most simple alkene will have two carbon atoms. There can not be only a single carbon atom in an alkene. Alkene has the general formula CnH2n where n is the number of carbon atoms in one molecule of the alkene.

  • If an alkene has 2 carbon atoms in its molecules, then n= 2, and its molecular formula will be C2H2(2) or C2H4.
  • If an alkene has 3 carbon atoms in its molecule, then n= 3, and its molecular formula will be C3H2(3) or C3H6.
  • If an alkene has 4 carbon atoms in its molecule, then n= 4, and its molecular formula will be C4H2(4) or C4H8.

Alkynes 

An alkyne is an unsaturated hydrocarbon with two carbon atoms connected together by a triple bond. Alkynes have a triple bond between two carbon atoms that are formed by sharing three pairs of electrons, resulting in a total of six electrons. 

Since they have a triple bond between two carbon atoms, ethyne and propyne are alkynes. Since an alkyne has a triple bond between two carbon atoms, the molecule of the most simple alkyne will have two carbon atoms. There can not be only a single carbon atom in an alkyne. Alkyne has the general formula CnH2n-2 where n is the number of carbon atoms in one molecule of the alkyne.

  • If an alkyne has 2 carbon atoms in its molecules, then n= 2, and its molecular formula will be C2H2(2)-2 or C2H2.
  • If an alkyne has 3 carbon atoms in its molecules, then n= 3, and its molecular formula will be C3H2(3)-2 or C3H4.
  • If an alkyne has 4 carbon atoms in its molecules, then n= 4, and its molecular formula will be C4H2(4)-2 or C4H6.

The simplest alkene is ethene and the simplest alkyne is ethyne.

Structural formulae of ethene and ethyne.

Sample Questions

Question 1: Mention an important difference between a saturated hydrocarbon and an unsaturated hydrocarbon.

Answer: 

Saturated hydrocarbons have only single bonds and are unreactive whereas unsaturated hydrocarbons have double or triple bonds and are quite reactive.

Question 2: How many carbon atoms does the simplest alkene have?

Answer:

An alkene has a double bond between two carbon atoms, so a simplest alkene will have two carbon atoms.

Question 3: Mention an important difference between an alkane and alkene.

Answer:

An alkane has carbon-carbon single bonds only and an alkene has carbon-carbon double bonds only.

Question 4: Identify if the given compound C3H4 is an alkene or alkyne.

Answer:

The alkenes have carbon-carbon double bonds and their general formula is CnH2n. The alkynes have carbon-carbon triple bonds and their general formula is CnH2n-2. Here in the given compound n= 3. Now put n= 3 in the general formula of alkene, we get C3H2(3) i.e., C3H6 which does not match the given compound, so it is not alkene. Now put n= 3 in the general formula of alkyne, we get C3H2(3)-2 i.e., C3H4 which is the given compound. So the given compound is an alkyne.

Question 5: Write the molecular formula of alkane, if the hydrocarbon molecule has 3 carbon atoms.

Answer:

The general formula of alkane is CnH2n+2 where n is the number of carbon atoms in a molecule. Given that there are 3 carbon atoms in the given hydrocarbon, so  n= 3. Now put n= 3 in the general formula of alkane, we get C3H2(3)+2 i.e., C3H8. So the molecular formula of alkane having 3 carbon atoms is C3H8.


Last Updated : 26 Oct, 2021
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