Other Hybrid Orbitals
Hybrid orbitals can be formed by mixing more than just two simple
atomic orbitals. If an s and two p orbitals combine, three hybrid
orbitals, each similar in shape to the sp hybrids, are formed. they are
called sp2 hybrid orbitals, the superscript 2
specifying the number of p orbitals taking part in the formation
of the hybrids. Also, notice that the number of hybrids is the set is
equal to the number of simple atomic orbitals from which the hybrids are
formed.
BCl3 is a molecule in which the central boron atom
uses sp2 hybrids for bonding. A boron atom has the valence
shell configuration
To form three bonds, boron must have three half-filled orbitals,
so its 2s electrons must become unpaired. The resulting half-filled s
and p orbitals then become hybridized.
A chlorine atom has the valence shell configuration 1s2 2s2 2p5 ,
the half-filed 3pz orbital of each chlorine overlaps with one of the sp2
hybrids of boron to give the molecule.
These bonds are illustrated below. The geometry of the BCl3
molecules is planar triangular because all three hybrid orbitals fit
nicely into the plane of the equator, 120o apart.
The list below shows important types of hybrid orbitals. The
directional properties of the various hybrids are also shown.
sp hybrids 
sp2 hybrids 
sp3 hybrids 
sp3d hybrids 
sp3d2 hybrids 
The bonds in the ethane molecule. Notice the overlap in the
orbitals. The degree of overlap of the sp3 orbitals in the
carbon-carbon bond does not appreciably affect the rotation of the two
CH3- groups.
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