Chemistry XI Content
CHEMISTRY OF METHANE
| 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.
| 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.
| Bond Angles:
HCH-bond angles are 109.5o.
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
| 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
Replacement of halogen atom with H-atom of an organic compound is called Halogenation. It is a substitution reaction.
CH4 + Cl2 CH3Cl + HCl (chloro methane)
CH3Cl + Cl2 CH2Cl2 +HCl (dichloro methane)
CH2Cl2 + Cl2 CHCl3 + HCl (chloroform)
CHCl3 + Cl2 CCl4 +HCl (carbon tetra chloride)
It is a photochemical reaction.
In the presence of sunlight Cl2 molecule undergoes homolytic fission to produce Cl-free radical.
Cl-Cl Clo + Clo (free radical)
Chlorine free radical attacks methane molecule to produce methyl free radical.
CH4 + Clo CH3o + HCl
CH3o + Cl2 CH3Cl + HCl
This reaction comes to halt whe
n any two free radicals combine.
Clo + Clo Cl2
CH3o + Clo CH3-Cl
CH3o + CH3o CH3-CH3
Since it is a chain reaction, therefore, it gives a mixture of different compounds.
| 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.
Manufacture of methyl alcohol.