Chemical Bonding and
Molecular Geometry
Valence-Shell Electron-Pair Repulsion
(VSEPR) Theory
-
Electron pairs repel each other, both bond pairs and unshared
(lone pairs)
-
Electron pairs assume orientations that minimize repulsions.
Applying VSEPR Theory
1. Draw a Lewis structure
2. Determine the number of electron groups around the
central atom and identify them as being either bond
pairs or lone pairs.
3. Establish the electron group geometry around the
central atom-linear,trigonal-planar,tetrahedral
4. Determine the molecular geometry from the
positions around the central atom occupied by the
other atomic nuclei.
Valence shell electron pair repulsion (VSEPR) model:
Predict the geometry of the molecule from the repulsions between
the electron (bonding and nonbonding) pairs.
# of atoms
bonded to
central atom
2
# lone
pairs on
central atom
Arrangement of
electron pairs
Molecular
Geometry
0
linear
linear
B
B
10.1
Cl
Be
Cl
0 lone pairs on central atom
2 atoms bonded to central atom
10.1
VSEPR
# of atoms
bonded to
central atom
2
3
# lone
pairs on
central atom
Arrangement of
electron pairs
Molecular
Geometry
0
linear
linear
0
trigonal
planar
trigonal
planar
10.1
10.1
VSEPR
# of atoms
bonded to
central atom
# lone
pairs on
central atom
3
0
2
1
Arrangement of
electron pairs
Molecular
Geometry
trigonal
planar
trigonal
planar
trigonal
planar
bent
10.1
VSEPR
# of atoms
bonded to
central atom
# lone
pairs on
central atom
Arrangement of
electron pairs
Molecular
Geometry
2
0
linear
linear
3
0
trigonal
planar
trigonal
planar
4
0
tetrahedral
tetrahedral
10.1
10.1
VSEPR
# of atoms
bonded to
central atom
# lone
pairs on
central atom
4
0
3
1
Arrangement of
electron pairs
Molecular
Geometry
tetrahedral
tetrahedral
tetrahedral
trigonal
pyramidal
10.1
10.1
Generic
Formula
Hybrid Atomic Orbitals
(1931 - Linus Pauling)
•Proposed that the outermost (valence) orbitals of an atom could be combined to form hybrid atomic orbitals.
Sigma bond (
The end-to-end overlapping of an s orbital with a p orbital to form a sp hybrid orbital.
Pi bond (
) - The side-to-side overlapping of two p orbitals.
•Single bonds are made up of one sigma bond.
•Double bonds are made up of one sigma bond and one pi bond.
•Triple bonds are made up of one sigma bond and two pi bonds.
Hybridization - A mixture of two or more atomic orbitals.
Numbe
of Place
Where
Electron
are
Found
MX
1
MX2
2
MX3
3
MX2E
3
MX4
4
MX3E
4
MX2E2
4
MX5
5
MX4E
5
MX3E2
5
MX2E3
5
MX6
6
MX5E
6
MX4E
6