Notes 4. Carbon and its Compounds - Hydrocarbons | Class 10 Science - Toppers Study

Hydrocarbons

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Hydrocarbons: All carbon compounds which contain just carbon and hydrogen are called hydrocarbons.

                  

Formulae of organic compounds:

(i) General formula: General formula represents a function for n numbers of each atom in a molecule. 

Example: for alkane: C_nH_2n+2

(ii) Molecular formula: Molecular formula represents actual number of atoms of a molecule. 

Example: For Ethane: C₂H₆

(iii) Condensed formula: Condensed formula represents group of atoms linked together to each carbon atom. 

Example: For Ethane: CH₃CH₃

(iv) Structural formula: It represents exact arrangement of atom of a molecule. 

Example: For Ethane: 

(v) Electronic formula: Electronic formula represents the sharing of electrons amongs atoms of a molecules. 

Example: For Ethane: 

Saturated Carbon Compounds: 

Compounds of carbon, which are linked by only single bonds between the carbon atoms are called saturated compounds.

Example: Alkanes like methane, Ethane, propane butane etc.

General formula for Alkanes: C_nH_2n+2

Using formula for Methane;

C_nH_2n+2

Putting n =1 we get

C₁H_{2x1 + 2}

CH₄

Similarily; 

For Ethane:

Putting n =2 we get

C₂H_{2x2 + 2}

C₂H₆

Similarily we can find molecular formula for propane, butane, pentane and so on ....... 

Alkanes: The saturated hydrocarbons in which carbon atom linked together with single bond are called alkenes.

Name of Alkanes	Molecular Formula	Condensed structural Formula
Methane	CH4	CH4
Ethane	C2H6	CH3CH3
Propane	C3H8	CH3CH2CH3
Butane	C4H10	CH3CH2CH2CH3
Pentane	C5H12	CH3CH2CH2CH2CH3
Hexane	C6H14	CH3CH2CH2CH2CH2CH3
Heptane	C7H16	CH3CH2CH2CH2CH2CH2CH3
Octane	C8H18	CH3CH2CH2CH2CH2CH2CH2CH3
Nonane	C9H20	CH3CH2CH2CH2CH2CH2CH2CH2CH3
Decane	C10H22	CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Structure of Methane (single bond);

      

Single carbon atom has four unsatisfied valency Linked with Hydrogen atom like figure. 

                                               

Electrone Dot strucuture of Methane

 

Structure of Ethane (single bond);

  C - C [ carbon atoms linked together witha single bond] 

Next Linked with Hydrogen atom to carbon unsatisfied valency like given figure;  

             

                             

Electron Dot structure of Ethane 

Structure of propane (single bond);

Structure of Butane (single bond);

Structure of pentane (single bond);

Structure of hexane (single bond);

Unsaturated Carbon Compounds: 

Compounds of carbon having double or triple bonds between their carbon atoms are called unsaturated compounds.

Example: Alkenes like and Alkynes;

Structure of alkenes (Double bond);

General Formula for Alkenes: C_nH_2n

The simplest Alkenes is Ethene;

So Ethene has 2 carbon atoms; 

Now putting n = 2 in general formula;

C₂H_2x2 = C₂H₄

Propene has 3 carbon atoms;

Now putting n = 3 in general formula;

 C₃H_2x3 = C₃H₆

Similarily we can find the molecular formula for other Alkenes like butene, pentene and hexene etc.

Alkenes: The unsaturated hydrocarbons which contain one or
more double bonds are called alkenes.

Name of Alkenes	Molecular Formula	Condensed structural Formula
Ethene	C2H4	CH2=CH2
Propene	C3H6	CH3CH=CH2
Butene	C4H8	CH3CH2CH=CH2
Pentene	C5H10	CH3CH2CH2CH=CH2
Hexene	C6H12	CH3CH2CH2CH2CH=CH2
Heptene	C7H14	CH3CH2CH2CH2CH2CH=CH2
Octene	C8H16	CH3CH2CH2CH2CH2CH2CH=CH2
Nonene	C9H18	CH3CH2CH2CH2CH2CH2CH2CH=CH2
Decene	C10H20	CH3CH2CH2CH2CH2CH2CH2CH2CH=CH2

Structural Formula of Alkene: 

Name of Alkenes	Molecular Formula	Structural Formula
Ethene	C2H4
Propene	C3H6
Butene	C4H8
Pentene	C5H10
Hexene	C6H12
Heptene	C7H14
Octene	C8H16
Nonene	C9H18
Decene	C10H20	​

Electron Dot Sructure of Ethene: 

    

              Ethene (C₂H₄)

Electron Dot Sructure of Propene: 

                        Prooene (C₂H₄)

Similarily We can draw electron dot structure of other Akenes; 

Structure of Alkynes (Triple Bond):

General formula of Alkynes: C_nH_2n-2

The simplest alkynes is Ethyne;

Ethyne has two carbon atoms. Hence, Using the formula;

Putting n = 2 for Ethyne,

C₂H_2x2-2 = C₂H₂

  ∴ Ethyne = C₂H₂

Similarily we can find Propyne; 

Putting n=3 for Propyne; 

C₃H_2x3-2 = C₃H₄

  ∴ Propyne = C₃H₄

Alkynes: 

Name of Alkenes	Molecular Formula	Condensed structural Formula
Ethyne	C2H2	CH≡CH
Propyne	C3H4	CH≡CCH3
1-Butyne	C4H6	CH≡CCH2CH3
1-Pentyne	C5H8	CH≡CCH2CH2CH3
1-Hexyne	C6H10	CH≡CCH2CH2CH2CH3
1-Heptyne	C7H12	CH≡CCH2CH2CH2CH2CH3
1-Octyne	C8H14	CH≡CCH2CH2CH2CH2CH2CH3
1-Nonyne	C9H16	CH≡CCH2CH2CH2CH2CH2CH2CH3
1-Decyne	C10H18	CH≡CCH2CH2CH2CH2CH2CH2CH2CH3

Long chain formula is abbreviated as bellow;

[Nonyne] CH≡CCH₂CH₂CH₂CH₂CH₂CH₂CH₃ can be written as  

CH≡C (CH₂)₆CH₃

similarily;

[Decyne] CH≡CCH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₃ can be written as 

CH≡C (CH₂)₇CH₃

Defferences between saturated and unsaturated carbon compound:

Saturated Compound	Unsaturated Compound
1. It has single bond between carbon atoms. 2. There occurs substitution reaction in it. 3. Example: Alkanes. 4. They are less reactive than the unsaturated carbon compound.	1. It has double and triple bond between carbon atoms. 2. There occurs addition reaction in it. 3. Example: Alkenes, Alkynes. 4. They are more reactive than the saturated carbon compounds.