Ethene

CHEMISTRY OF ETHENE
INTRODUCTION
  Molecular formula = C2H4
  Empirical formula = CH2
  Molecular mass = 28
  Empirical formula mass = 14
  Homologous series = alkene
ORBITAL STRUCTURE
OF ETHENE
 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:Orbital structure of ethene
 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 vapours of ethyl alcohol over 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
CHEMICAL PROPERTIES
 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+C
H2-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 colourless 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-)