http://www.ck12.org Chapter 9. Covalent Bonding
Boron trifluoride (BF 3 ) is predicted to have a trigonal planar geometry by VSEPR. First, a paired 2selectron is
promoted to an empty 2porbital.
This is followed by hybridization of the three occupied orbitals to form a set of threesp^2 hybrids, leaving the 2pz
orbital unhybridized. The choice of whichporbital to leave unhybridized is arbitrary, but 2pzis conventionally
chosen in the case ofsp^2 hybrids.
The geometry of thesp^2 hybrid orbitals is trigonal planar, with the large lobe of each orbital pointing toward one
corner of an equilateral triangle (Figure9.40). The angle between any two of the hybrid orbital lobes is 120°. Each
can bond with a 2porbital from a fluorine atom to form the trigonal planar BF 3 molecule.
FIGURE 9.40
The process ofsp^2 hybridization involves
the mixing of onesorbital with a set of
twoporbitals (pxandpy) to form a set of
threesp 2 hybrid orbitals. Each large lobe
of the hybrid orbitals points to one corner
of a triangle.Other molecules with a trigonal planar electron domain geometry also formsp^2 hybrid orbitals. For example, the
electron domain geometry of ozone (O 3 ) is trigonal planar, although the presence of a lone pair on the central oxygen
atom makes the molecular geometry bent. The hybridization of the central O atom of ozone issp^2.
A beryllium hydride (BeH 2 ) molecule is predicted to be linear by VSEPR. The beryllium atom contains only paired
electrons, so it must also undergo hybridization. One of the 2selectrons is first promoted to an empty 2porbital.