Chemistry XI Content

General
Organic Chemistry
Nomenclature of Organic Compounds
Introduction to Hydrocarbons
An Introduction to Benzene
Alkyl Halides
Inorganic Chemistry
Physical Chemistry
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Methane


CHEMISTRY OF METHANE
INTRODUCTION
 Molecular formula = CH4
Molecular mass = 16
Empirical formula = CH4
Empirical formula mass = 16
State: Gas at room temperature.
Occurrence: marsh, stagnant ponds.
It is the major constituent of natural gas. Natural gas contains 94.6% methane.
ORBITAL STRUCTURE
OF METHANE
    Composition of methane molecule:
Methane molecule consists of one carbon and four hydrogen atoms (CH4).
    Nature of Hybridization:
In methane C-atom is Sp3-hybridized. One s-orbital and three p-orbitals (2px,2py,2pz) of carbon atom    undergo Sp3-hybridization to produce four Sp3-hybrid orbitals. These Sp3-hybrid orbitals are 109.5o a    part.
    Sigma bond Formation:
Each Sp3-hybrid orbital overlaps 1s-orbital of H-atoms. In this way four s-bonds are produced    between C and four H-atoms.
    Geometry of methane:
Methane molecule is tetrahedral in structure in which carbon is central atom and four H-atoms are    surrounding it in three-dimensions.
methane2

methane1
   Bond Angles:
HCH-bond angles are 109.5o.
   Bond Length:
All C-H bonds are 1.09Ao.
METHOD OF PREPARATION OF METHANE
– FROM GRIGNARD’S REAGENT:
     Methane can be prepared by the hydrolysis of “Methyl Magnesium Iodide”.
CH3-Mg-I + HOH irreversible_arrow CH4 + Mg-I-OH
– BY THE CATALYTIC REDUCTION OF METHYL IODIDE:
   CH3-I + H2   irreversible_arrow CH4 +HI
– BY THE REDUCTION OF METHYL IODIDE WITH NASCENT HYDROGEN:
CH3I + 2[H] irreversible_arrow CH4 + HI
– BY SODIUM ACETATE AND NaOH:
   CH3COONa + NaOH irreversible_arrow Na2CO3 +CH4
CHEMICAL PROPERTIES
OF METHANE
   COMBUSTION REACTION:
   Combustion of methane is an exothermic reaction in which a large amount of energy is liberated. Due to    this property, methane is used as a domestic and industrial fuel.
               CH4 + 2O2 irreversible_arrow CO2 + 2H2O
   HALOGENATION:
   Replacement of halogen atom with H-atom of an organic compound is called Halogenation. It is a    substitution reaction.
   CHLORINATION:
                    CH4 + Cl2 irreversible_arrow CH3Cl + HCl (chloro methane)
CH3Cl + Cl2 irreversible_arrow CH2Cl2 +HCl (dichloro methane)
CH2Cl2 + Cl2 irreversible_arrow CHCl3 + HCl (chloroform)
CHCl3 + Cl2 irreversible_arrow CCl4 +HCl (carbon tetra chloride)
   MECHANISM:
   It is a photochemical reaction.
   INITIATION STEP:
   In the presence of sunlight Cl2 molecule undergoes homolytic fission to produce Cl-free radical.
               Cl-Cl irreversible_arrow Clo + Clo (free radical)
   PROPAGATION STEP:
   Chlorine free radical attacks methane molecule to produce methyl free radical.
               CH4 + Clo irreversible_arrow CH3o + HCl
CH3o + Cl2 irreversible_arrow CH3Cl + HCl
   TERMINATION STEP:
   This reaction comes to halt when any two free radicals combine.
               Clo + Clo irreversible_arrow Cl2
CH3o + Clo irreversible_arrow CH3-Cl
CH3o + CH3o irreversible_arrow CH3-CH3
   OUTPUT:
   Since it is a chain reaction, therefore, it gives a mixture of different compounds.
PHYSICAL PROPERTIES
OF METHANE
   Methane is a colorless, odorless and non-poisonous gas.
   Melting point = -182.5oC.
   Boiling point = -169.5oC.
   Its molecule is symmetrical.
   It is lighter than air.
USES OF METHANE
– Domestic and industrial fuel.
– Shoe polish.
– Printing ink.
– Tyre manufacturing.
– Manufacture of methyl alcohol.
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