That means there exists a sigma (σ) bond and a pi (π) bond between two
      carbon atoms in ethene molecule. Hence, the molecule ethene (C2H4) is 
      
                   figure of
      
                                                          C2H4

      The common name for Ethene is Ethylene.
   
 
     sp hybridisation
   
            Each carbon is only joining to two other atoms rather than four (as in
      methane or ethane) or three (as in ethene). Here the carbon atoms hybridise
      their outer orbitals before forming bonds, this time they only hybridise
      two of the orbitals.
      
            They use the ‘s’ orbital (2s) and one of the 2p orbitals, but leave the
      other 2p orbitals unchanged. The new hybrid orbitals formed are called sp
      hybrid orbitals, because they are made by an s-orbital and a p-orbital
      reorganizing themselves.
      
             How do you explain the ability of carbon atom to form one single
      bond and one triple bond?

             To know the ability of ‘C’ to form one single bond and one triple bond,
      let us consider ethyne (acetylene or C2H2) molecule as our example.
      
   
        
                                figure of C2H2