CHEM 107, Fall 2016
sp3 Hybrid Orbitals
Class #22
Molecular Geometry
CHEM 107
L.S. Brown
Texas A&M University
Other Hybridizations
•  Mix 4 orbitals, get 4 new identical
orbitals
•  Energy between s and p
•  Angles of 109.5°
•  Tetrahedral shape
•  Let’s us explain bonding in methane
(and lots of other molecules, too)
Steric Number & Hybridization
•  We can form other hybrids
s + 3p’s ! sp3
s + 2p’s ! sp2
s + p ! sp
•  Same ideas, but get orbitals at different
angles
Orbital Orientation vs.
Molecular Geometry
•  Molecular shape based on position of
ATOMS
•  All hybrids used for bonds à molecular
geometry same as orbital orientation
•  Lone pairs on central atom à molecular
shape differs from orbital orientation
© 2016, L.S. Brown
Steric Number of 2
•  sp hybrids, linear orientation
•  No lone pairs à linear molecule
CO2
1
CHEM 107, Fall 2016
Steric Number of 3
•  sp2 hybrids, trigonal planar orientation
•  No lone pairs à trigonal planar
molecule
BF3, NO3
–
•  One lone pair à bent triatomic
molecule
O3, NO2
Steric Number of 5
•  sp3d hybrids, trigonal bipyramid
orientation
•  No lone pairs à trigonal bipyramid
molecule
PCl5
•  Lone pairs: Positions not all equivalent!
Steric Number of 6
•  sp3d2 hybrids, octahedral
•  No lone pairs à octahedral
SF6
•  One lone pair à square pyramid
Steric Number of 4
•  sp3 hybrids, tetrahedral orientation
•  No lone pairs àtetrahedral
CH4, NH4+
•  One lone pair à trigonal pyramid
NH3
•  Two lone pairs à bent
H 2O
Steric Number of 5
•  One lone pair à “seesaw” molecule
SF4
•  Two lone pairs à T-shape molecule
ClF3
•  Three lone pairs à Linear molecule
I3–
Multiple Bonds
•  How can orbitals overlap to form double
or triple bonds?
•  Start with a simple example: C2H4
•  First draw a Lewis structure
ClF5
•  Two lone pairs à square planar
XeF4
© 2016, L.S. Brown
2
CHEM 107, Fall 2016
Ethylene - C2H4
H
C
Ethylene - C2H4
H
H
H
H
•  Double bond?
C
H
H
C
•  Carbons have steric number of 3 à sp2
•  Overlap of sp2 orbitals from each
carbon forms single bond.
•  Double bond?
C
H
•  “Sideways” overlap of unhybridized p
orbitals from carbon atoms
•  “π bond”
Acetylene - C2H2
Acetylene - C2H2
H
H
C
C
H
•  Carbons have steric number of 2 à sp
•  “Sigma bond” from
overlap of 2 sp hybrids
•  Triple bond?
C
C
H
•  Triple bond à 3 bonds
•  Need 2 π bonds in addition to σ bond
•  “Sideways” overlap of unhybridized p
orbitals on carbon atoms, this time
using 2 p orbitals from each carbon (px
and py )
Multiple Bonds
Large Molecules
•  In orbital overlap (or “localized bond”)
model:
– Single bond is a σ bond
– Double bond consists of a σ bond and
a π bond
– Triple bond consists of a σ bond and
two π bonds
•  Use same ideas as with small
molecules
•  Predict geometry around each inner
atom
•  Work your way up to a shape for the full
molecule
© 2016, L.S. Brown
3
CHEM 107, Fall 2016
Peroxyacetyl nitrate
O
H O
H C C O O N O
H
•  Finish Lewis structure
•  Determine hybridization of all inner
atoms
•  Predict bond angles
© 2016, L.S. Brown
4