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. | ||
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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 ![]() | ||
– BY THE CATALYTIC REDUCTION OF METHYL IODIDE: CH3-I + H2 ![]() – BY THE REDUCTION OF METHYL IODIDE WITH NASCENT HYDROGEN: CH3I + 2[H] ![]() – BY SODIUM ACETATE AND NaOH: CH3COONa + NaOH ![]() | ||
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 ![]() HALOGENATION: Replacement of halogen atom with H-atom of an organic compound is called Halogenation. It is a substitution reaction. CHLORINATION: CH4 + Cl2 ![]() CH3Cl + Cl2 ![]() CH2Cl2 + Cl2 ![]() CHCl3 + Cl2 ![]() 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 ![]() PROPAGATION STEP: Chlorine free radical attacks methane molecule to produce methyl free radical. CH4 + Clo ![]() CH3o + Cl2 ![]() TERMINATION STEP: This reaction comes to halt when any two free radicals combine. Clo + Clo ![]() CH3o + Clo ![]() CH3o + CH3o ![]() 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. |