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.