http://www.ck12.org Chapter 9. Covalent Bonding
Again, the promotion of an electron in the carbon atom occurs in the same way. However, the hybridization now
involves only the 2sorbital and the 2pxorbital, leaving the 2pyand the 2pzorbitals unhybridized.
The sigma bond between the two carbon atoms is formed fromsphybrid orbitals, and the remaining hybrid orbitals
form sigma bonds to the two hydrogen atoms. Both thepyand thepzorbitals on each carbon atom form pi bonds
with each other. As with ethene, these side-to-side overlaps are not directly on the line between the two bonded
atoms. Additionally, these two pi bonds are perpendicular to one another (Figure9.45); one pi bond is above and
below the line of the molecule, while the other is in front of and behind the page.
FIGURE 9.45
The C 2 H 2 molecule contains a triple bond
between the two carbon atoms, one of
which is a sigma bond, and two of which
are pi bonds. The pi bonds come from
overlap between thepyand thepzorbitals
on each carbon.In general, single bonds between atoms are always sigma bonds. Double bonds are comprised of one sigma and one
pi bond. Triple bonds are comprised of one sigma bond and two pi bonds.
Lesson Summary
- Valence bond theory describes the formation of covalent bonds in terms of the overlap of singly occupied
atomic orbitals.