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.
Orbital structure of methane

 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  CH4 + Mg-I-OH
 BY THE CATALYTIC REDUCTION OF METHYL IODIDE:
    CH3-I + H2    CH4 +HI
 BY THE REDUCTION OF METHYL IODIDE WITH NASCENT HYDROGEN:
 CH3I + 2[H]  CH4 + HI
 BY SODIUM ACETATE AND NaOH:
     CH3COONa + NaOH  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  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  CH3Cl + HCl (chloro methane)
 CH3Cl + Cl2  CH2Cl2 +HCl (dichloro methane)
 CH2Cl2 + Cl2  CHCl3 + HCl (chloroform)
 CHCl3 + Cl2  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  Clo + Clo (free radical)
 PROPAGATION STEP:
  Chlorine free radical attacks methane molecule to produce methyl free radical.
   CH4 + Clo  CH3o + HCl
 CH3o + Cl2  CH3Cl + HCl
 TERMINATION STEP:
  This reaction comes to halt when any two free radicals combine.
   Clo + Clo  Cl2
 CH3o + Clo  CH3-Cl
 CH3o + CH3o  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, odourless 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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