Molecular Predicting Geometry
1. Draw Lewis structure for molecule.
2. Count number of lone pairs on the central atom and
number of atoms bonded to the central atom.
3. Use VSEPR to predict the geometry of the molecule.
10.1
Predicting Molecular Geometry
Example: What is the molecular geometry of SO2 ?
O
S
trigonal
planar
O
bent
AB2E
1. Draw Lewis structure for molecule.
2. Count number of lone pairs on the central atom and number of
atoms bonded to the central atom.
3. Use VSEPR to predict the geometry of the molecule.
10.1
Predicting Molecular Geometry
Example: What is the molecular geometry of SF4?
trigonal
bipyramidal
F
F
AB4E
S
distorted
tetrahedron
F
F
1. Draw Lewis structure for molecule.
2. Count number of lone pairs on the central atom and number of
atoms bonded to the central atom.
3. Use VSEPR to predict the geometry of the molecule.
10.1
1
Recall: we talked about how water has a dipole:
2
e
=
e
+
+
electrons are shared
unequally btw O & H
+
4.1
Dipole Moments and Polar Molecules
electron poor
region
electron rich
region
H
F
+
The moment dipole of a molecule is given by:
=Qxr
where Q is the charge and r is the distance between charges.
The unit is the Debye, where 1 D = 3.36 x 10-30 C m.
10.2
10.2
2
10.2
Which of the following molecules have a dipole moment?
H2O, CO2, SO2 , and CH4
O
H
H
dipole moment
polar molecule
S
O
O
dipole moment
polar molecule
H
O
C
O
no dipole moment
nonpolar molecule
H
C
H
H
no dipole moment
nonpolar molecule
10.2
Does BF3 have a
dipole moment?
10.2
3
Does CH2 Cl2 have
a dipole moment?
10.2
10.2
Lewis theory explains bonding as sharing of two
electrons between the two atoms, but offers no
explanation why and treats all single bonds equally.
Overlap Of
Bond Dissociation Energy
Bond Length
H2
436.4 kJ/mole
74 pm
2 1s
F2
150.6 kJ/mole
142 pm
2 2p
HF
568.2 kJ/mole
92 pm
1s + 2p
Valence bond theory bonds are formed by
sharing of e- from overlapping atomic orbitals.
10.3
4
Change in Potential Energy of Two Hydrogen Atoms
as a Function of Their Distance of Separation
10.3
Change in electron
density as two hydrogen
atoms approach each
other.
10.3
5