Molecular formula = C2H4 Empirical formula = CH2 Molecular mass = 28 Empirical formula mass = 14 Homologous series = alkene
COMPOSITION OF ETHENE: Ethene molecule consists of two carbon atoms and four H-atoms i.e. CH2=CH2 NATURE OF HYBRIDIZATION: In ethene molecule each C-atom is Sp2-hybridized. Due to Sp2-hybridization each C-atom generates three Sp2-hybrid orbitals. In this way there exist six Sp2-hybrid orbital. These Sp2-orbital are arranged in trigonal order and 120o apart. Remaining ‘2pz‘ unhybrid orbital of carbon atom are placed perpendicular to the plane of Sp2-orbitals. SIGMA BOND FORMATION: One Sp2-hybrid orbital of C-atom overlaps with One Sp2-hybrid orbital of second C-atom to produce one sigma bond between two carbon atoms. Remaining two Sp2-orbitals overlap with two H-atom to produce sigma bond. ‘2pz‘ orbitals of two C-atoms are un-hybridized and make parallel overlapping to produce pi-bond as shown below:
BOND LENGTH: C=C bond length is 1.34A. C-H bond length is 1.09A.
METHODS OF PREPARATION
BY VICINAL DIHALIDE: When vicinal dihalide is heated with zinc dust, two halide atoms are removed from the compound and ethene is formed. CH2-CH2 + Zn CH2=CH2 + ZnCl2 | | Cl Cl BY THE REDUCTION OF ETHYNE: Under control conditions, ethyne adds two H-atoms to form ethene in the presence of Nickel(Ni) at 200oC. + H2 H-C=C-H BY THE DEHYDROHALOGENATION OF ALKYL HALIDE: When alkyl halide (ethyl chloride) is treated with alcoholic KOH, b-elimination takes place and ethene is obtained. CH3-CH2Cl + KOH CH2=CH2 + KCl + H2O BY THE DEHYDRATION OF ALCOHOL: When ethyl alcohol is heated with conc.H2SO4 at 170oC, dehydration of alcohol takes place and ethene is formed. C2H5OH C2H4 + H2O
OR Ethyl alcohol may also be converted into ethene by passing vapors of ethyl alcohol over a catalyst (Al2O3, H3PO4/Al2O3). The reaction is carried out at 350C in the presence of Al2O3 and at 250C when H3PO4/Al2O3 is used. C2H5OH C2H4 + H2O
ADDITION REACTIONS OF ETHENE: Addition of chlorine: CH2=CH2 + Cl2 CH2Cl-CH2Cl (1,2-dichloroethane) Addition of bromine: CH2=CH2 +Br2 CH2Br-CH2Br (1,2-dibromoethane) Addition of iodine: CH2=CH2 + I2 CH2I-CH2I (1,2-diiodoethane) Order of reactivity: Cl2 > Br2 > I2 ADDITION OF HYDROGEN: CH2=CH2 + H2 CH3-CH3 ADDITION OF H2SO4: CH2=CH2 + H2SO4 CH3-CH2-HSO4 ADDITION OF H2O: CH2=CH2 + HOH CH3-CH2-OH ADDITION OF HCl: CH2=CH2 + HCl CH3-CH2-Cl ADDITION OF HBr: CH2=CH2 + HBr CH3-CH2-Br ADDITION OF HI: CH2=CH2 + HI CH3+CH2-I ADDITION OF HYPOHALOUS ACID: CH2=CH2 + HOCl OH-CH2-CH2-Cl (Ethane chlorohydrin) REACTION WITH CHLORINE WATER: When Cl2 is mixed with water, two molecules of acids are formed. Cl2 + H2O HCl + HOCl CH2=CH2 + HCl CH3-CH2-Cl CH2=CH2 + HOCl OH- CH2-CH2-Cl COMBUSTION REACTION: CH2=CH2 + 3O2 2CO2 + 2H2O OXIDATION REACTION: When ethene is treated with KMnO4 solution, purple colour of KMnO4 disappears due to deformation of a colorless compound “Ethylene Glycol”. CH2=CH2 + H2O +[O] OH-CH2-CH2-OH FORMATION OF MUSTARD GAS: b,b-Dichloroethyl Sulphide is commonly known as “Mustard gas”. It is a very poisonous gas. It can produce blisters on skin. 2CH2=CH2 + S2Cl2 Cl-CH2-CH2-S-CH2-CH2-Cl + S POLYMERIZATION: n(CH2=CH2) n(-CH2-CH2-)