Class 10, Science, Chapter-4, Lecture-5, Properties of Hydrocarbons (Notes)
ISOMERS:
Compounds having the same molecular formula but different structural arrangements of atoms in them are termed as isomers.
Example: butane and 2-methylpropane are isomers.
STRUCTURAL ISOMERS:
Compounds having the same molecular formula, but different structural formulas are termed as structural isomers.
Example: butane and 2-methylpropane are structural isomers
ISOMERS OF PENTANE:
Structural Formula |
IUPAC Name |
Common Name |
---|---|---|
${\rm{C}}{{\rm{H}}_3} - {\rm{ C}}{{\rm{H}}_2} - {\rm{C}}{{\rm{H}}_2} - {\rm{C}}{{\rm{H}}_2} - {\rm{C}}{{\rm{H}}_3}$ |
pentane |
n-Pentane |
$${\rm{C}}{{\rm{H}}_{\rm{3}}} - \mathop {{\rm{CH}}}\limits_{\mathop {\rm{|}}\limits_{{\rm{C}}{{\rm{H}}_{\rm{3}}}} }^{} - {\rm{C}}{{\rm{H}}_{\rm{2}}} - {\rm{C}}{{\rm{H}}_{\rm{3}}}$$ | 2-methylbutane | iso-pentane |
$${\rm{C}}{{\rm{H}}_{\rm{3}}} - \mathop {\rm{C}}\limits_{\mathop {\rm{|}}\limits_{{\rm{C}}{{\rm{H}}_{\rm{3}}}} }^{\mathop {{\rm{C}}{{\rm{H}}_{\rm{3}}}}\limits_{\rm{|}} } - {\rm{C}}{{\rm{H}}_{\rm{3}}}$$ | 2,2-dimethylpropane | neo-pentane |
CHEMICAL PROPERTIES OF HYDROCARBONS:
1. COMBUSTION:
Complete combustion takes place in the presence of excess of oxygen to produce carbondioxide and water.
$$\mathop {C{H_4}}\limits_{methane} + 2\mathop {{O_2}}\limits_{oxygen} \buildrel {} \over
\longrightarrow \mathop {C{O_2}}\limits_{carbondioxide} + 2\mathop {{H_2}O}\limits_{water} $$
$$\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{4}}}}\limits_{{\rm{ethene}}} {\rm{ + 3 }}\mathop {{{\rm{O}}_{\rm{2}}}}\limits_{{\rm{oxygen}}} \buildrel {} \over
\longrightarrow 2\mathop {{\rm{C}}{{\rm{O}}_{\rm{2}}}}\limits_{{\rm{carbondioxide}}} {\rm{ + 2 }}\mathop {{{\rm{H}}_{\rm{2}}}{\rm{O}}}\limits_{{\rm{water}}} $$
$$2{\rm{ }}\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{2}}}}\limits_{{\rm{ethyne}}} {\rm{ + 5 }}\mathop {{{\rm{O}}_{\rm{2}}}}\limits_{{\rm{oxygen}}} \buildrel {} \over
\longrightarrow {\rm{4}}\mathop {{\rm{C}}{{\rm{O}}_{\rm{2}}}}\limits_{{\rm{carbondioxide}}} {\rm{ + 2 }}\mathop {{{\rm{H}}_{\rm{2}}}{\rm{O}}}\limits_{{\rm{water}}} $$
Unsaturated hydrocarbons burn with a sooty flame.
Reason:
The percentage of carbon present in unsaturated hydrocarbons is more than that in a saturated hydrocarbon. Some of the carbons remain unburnt due to limited supply of oxygen. The unburnt carbon particles form the soot.
Unsaturated hydrocarbons burn with a yellow flame.
Reason:
The percentage of carbon present in unsaturated hydrocarbons is more than that in a saturated hydrocarbon. Some of the carbons remain unburnt due to limited supply of oxygen. The unburnt carbon particles glow when hot and give yellow colour to the flame.
2. ADDITION REACTION:
Unsaturated hydrocarbons undergo addition reaction in the presence of catalysts (PALLADIUM or NICKEL) to give saturated hydrocarbons.
$$\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{4}}}}\limits_{{\rm{ethene}}} {\rm{ + }}\mathop {{{\rm{H}}_{\rm{2}}}}\limits_{{\rm{hydrogen}}} \mathrel{\mathop{\kern0pt\longrightarrow}
\limits_{{\rm{Catalyst}}}^{{\rm{Nickel/Palladium}}}} \,\,\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{6}}}}\limits_{{\rm{ethane}}} $$
Hydrogenation:
The addition of hydrogen in the presence of catalysts (nickel) to convert unsaturated organic compounds into saturated organic compounds is termed as hydrogenation.
3. SUBSTITUTION REACTION with CHLORINE (CHLORINATION):
Saturated hydrocarbons undergo substitution reaction with chlorine in the presence of sunlight.
$$\mathop {{\rm{C}}{{\rm{H}}_{\rm{4}}}}\limits_{{\rm{methane}}} {\rm{ + }}\mathop {{\rm{C}}{{\rm{l}}_{\rm{2}}}}\limits_{{\rm{chlorine}}} \buildrel {{\rm{Sunlight}}} \over
\longrightarrow \,\mathop {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{Cl}}}\limits_{{\rm{chloromethane~or~methyl~chloride}}} $$