Download VSEPR Model (cont.)

Section 8.4 Molecular Shapes
• Summarize the VSEPR
bonding theory.
• Predict the shape of,
and the bond angles in,
a molecule.
• Define hybridization.
atomic orbital: the
region around an atom’s
nucleus that defines an
electron’s probable
location
VSEPR model
hybridization
The VSEPR model is used to determine
molecular shape.
VSEPR Model
• The shape of a molecule determines many
of its physical and chemical properties.
• Molecular geometry (shape) can be
determined with the Valence Shell Electron
Pair Repulsion model, or VSEPR model
which minimizes the repulsion of shared and
unshared electrons around the central atom.
VSEPR Model (cont.)
• Electron pairs repel each other and cause
molecules to be in fixed positions relative
to each other.
• Unshared electron pairs also determine the
shape of a molecule.
• Electron pairs are located in a molecule as far
apart as they can be.
VSEPR Theory
Types of e- Pairs (around central atom)


Bonding Areas - from bonds (single, double,
triple) all count as one pair
Lone pairs - nonbonding e-
Lone pairs repel
more strongly than
bonding pairs!!!
Determining Molecular Shape
Draw the Lewis Diagram.
Tally up e- pairs on central atom.

Single/double/triple bonds = ONE pair
(AREA)
Shape is determined by the # of
bonding AREAS and LONE PAIRS.
Know the 8 common shapes
& their bond angles!
Common Molecular Shapes
e- Tally
2 total
2 bond areas
0 lone pairs
LINEAR
BeH2
180°
Common Molecular Shapes
e- Tally
3 total
3 bond areas
0 lone pairs
BF3
TRIGONAL PLANAR
120°
Common Molecular Shapes
e- Tally
4 total
4 bond areas
0 lone pairs
CH4
TETRAHEDRAL
109.5°
Common Molecular Shapes
e- Tally
4 total
3 bond areas
1 lone pair
NH3
TRIGONAL PYRAMIDAL
107°
Common Molecular Shapes
e- Tally
3 total
2 bond areas
1 lone pair
SO2
BENT
<120°
Common Molecular Shapes
e- Tally
4 total
2 bond areas
2 lone pairs
H2O
BENT
104.5°
Common Molecular Shapes
e- Tally
5 total
5 bond areas
0 lone pairs
PCl5
TRIGONAL
BIPYRAMIDAL
120°/90°
Common Molecular Shapes
e- Tally
6 total
6 bond areas
0 lone pairs
SF6
OCTAHEDRAL
90°
Examples
PF3
4 total
3 bond areas
1 lone pair
F P F
F
TRIGONAL
PYRAMIDAL
107°
Examples
CO2
2 total
2 bond areas
0 lone pair
O C O
LINEAR
180°
Hybridization
Is the process by which s, p, and d orbitals
combine to form new identical orbitals
The hybridization is equal to the total
number of Bonding Areas and lone pairs
around the central atom in the molecule.
For example: water has two bonding areas
and two lone pairs of electrons, so we need 4
total hybrid orbitals = one s orbital and three
p orbitals = sp3
Hybridization
(cont.)
• Single, double, and triple
bonds occupy only one hybrid
orbital (CO2 with two double
bonds forms an sp hybrid
orbital).
Hybridization
(cont.)
Hybridization
(cont.)
Hybridization
(cont.)
Section 8.4 Assessment
The two lone pairs of electrons on a water
molecule do what to the bond angle between
the hydrogen atoms and the oxygen atom?
A. They attract the hydrogen atoms and
increase the angle greater than 109.5°.
0%
A
B
C
D
0%
0%
D
0%
A
D. They create resonance structures
with more than one correct angle.
C
C. They do no affect the bond angle.
A.
B.
C.
D.
B
B. They occupy more space and squeeze
the hydrogen atoms closer together.
Section 8.4 Assessment
The sp3 hybrid orbital in CH4 has what
shape?
A. linear
B. trigonal planar
D
A
0%
C
D. octahedral
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. tetrahedral