9.4. Hybridization of Atomic Orbitals http://www.ck12.org
The threesp^2 hybrid orbitals lie in one plane, while the unhybridized 2pzorbital is oriented perpendicular to that
plane. The bonding in C 2 H 4 is explained as follows. One of the threesp^2 hybrids forms a bond by overlapping
with the identical hybrid orbital on the other carbon atom. The remaining two hybrid orbitals form bonds by
overlapping with the 1sorbital of a hydrogen atom. Finally, the 2pzorbitals on each carbon atom form another
bond by overlapping with one another sideways.
It is necessary to distinguish between the two types of covalent bonds in a C 2 H 4 molecule. Asigma bond (σbond)
is a bond formed by the overlap of orbitals in an end-to-end fashion, with the electron density concentrated between
the nuclei of the bonding atoms. Api bond (πbond)is a bond formed by the overlap of orbitals in a side-by-
side fashion, with the electron density concentrated above and below the plane of the nuclei of the bonding atoms.
Pictured below (Figure9.44) are the two types of bonding in C 2 H 4. Thesp^2 hybrid orbitals are orange and thepz
orbital is green. Three sigma bonds are formed by each carbon atom with its hybrid orbitals. The pi bond is the
“second” bond of the double bond between the carbon atoms and is shown as an elongated blue lobe that extends
both above and below the plane of the molecule, which contains the six atoms and all of the sigma bonds.
FIGURE 9.44
The C 2 H 4 molecule contains five sigma
bonds and one pi bond. Sigma bonds
are formed by a direct overlap of bonding
orbitals, while a pi bond is formed by
a side-to-side overlap of unhybridizedp
orbitals.In a conventional Lewis electron-dot structure, a double bond is shown as two lines between the atoms, as in C=C.
It is important to realize, however, that the two bonds are different; one is a sigma bond, while the other is a pi bond.
Ethyne (C 2 H 2 ) is a linear molecule with a triple bond between the two carbon atoms. Since each carbon atom is
bonded to two other atoms and has no lone pairs, the hybridization of each carbon issp.