This is the hybridization seen in alkenes. The third p-orbital of each carbon is left unhybridized. This
is the orbital that participates in the π bond. The three sp^2 orbitals are oriented 120° apart, which
allows for maximum separation. We know that the unhybridized p-orbital is involved in the π
component of the double bond, but what about the hybrid orbitals? In ethene, two of the sp^2
hybridized orbitals will participate in C–H bonds, and the other hybrid orbital will line up with the π
bond and form the σ component of the C=C double bond.
Figure 3.6. sp^2 -Hybridized Orbitals
A molecule with these orbitals has trigonal planar geometry, and the one unhybridized p-orbital can
be used to form a π bond.sp
To form a triple bond, we need two of the p-orbitals to form π bonds, and the third p-orbital will
combine with the s-orbital to form two sp-orbitals, as shown in Figure 3.7. These orbitals have 50% s
character and 50% p character. These orbitals are oriented 180° apart, which explains the linear
structure of molecules containing sp-hybridized carbons. The two π bonds can be between the
carbon and one other atom (forming a triple bond, like ethyne), or between the carbon and two
different atoms (forming two double bonds in a row, like carbon dioxide). In both cases, the
molecule is linear about the sp-hybridized carbon.