21 Chemistry -- Chemical Bonding and Shapes of Molecules

Draw the orbital picture of Ethene


Draw the orbital picture of Ethene


Each carbon has two half-filled orbitals in ground state (1s2, 2s2, 2px1 2py 1, 2pz 0). It has four half-filled orbitals in excited state since one electron is promoted from 2s to empty 2p orbital during chemical combination (1s2, 2s2, 2px1 2py 1, 2pz 0).

Now, one 2s and two 2p orbitals undergo sp2 hybridization to form three sp2 hybrid orbitals of equivalent energy and identical shape and size which take trigonal planar geometry with bond angle 120º. Unhybridized 2pz half-filled orbital remains perpendicular to the plane of hybrid orbitals.



One half-filled sp2 orbital of one carbon atom overlaps with half-filled sp2 orbital of another carbon atom forming carbon to carbon sigma bond. Each half filled sp2 hybrid orbitals of both carbons atoms overlap with half-filled 1s orbital of four hydrogen atoms forming four carbon to hydrogen sigma bonds. The remaining half filled 2pz orbital of one carbon which is perpendicular to the plane of hybrid orbitals overlaps with that of another carbon atom laterally forming carbon to carbon pi bond. Hence, ethene is flat molecule (all carbon and hydrogen atoms lying in a plane) with pi electron cloud above and below the plane of the molecule. The geometry is trigonal planar with respect to each carbon.

 

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