9. Molecular Orbitals and      Molecular Structure   Previous PageNext Page
     Double Bonds and sp2 Hybridisation

Bond angles close to 120 suggest three equal orbitals in a plane. This geometry can be obtained by combining the s. orbital and two of the three p orbitals of each carbon into a set of three Sp2 hybrid atomic orbitals. The third, unhybridized p orbital extends vertically above and below the plane of the page. In ethylene, two of the three Sp2 orbitals on each carbon are combined with hydrogen Is orbitals, and the third is involved in the bond with the other carbon. These all are a- bonds because they are symmetrical about the individual bond axes. This s framework of the ethylene molecule uses ten of the twelve available bonding electrons, and all of the outer-shell atomic orbitals except one unhybridized 2p, orbital on each carbon.

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