Transcript Chapters 8 & 9

Chapters 9
Molecular Geometry &
Bonding Theories
Lewis structures can
be used to represent
bonds; however they do
NOT show the actual
3D arrangement with
correct bond angles!
VSEPR
Valence Shell Electron – pair Repulsion Model



Provides a description of the valence e- arrangement in
the molecule bases on Lewis structures.
Predicts the geometry of the molecule bases on e- pair
repulsion. Including:
• e- geometry : e- pairs repel each other and will
assume orientation about the atom to minimize
repulsion.
• Molecular geometry
• Bond angles
Provides a description of the type of atomic orbitals
used by atoms to share e- or to hold lone pair e- (nonbonding e-)
Bonding & Nonbonding electrons
Lone pair e-
Effect of Nonbonding e- on Bond Angles
Nonbonding pair of e- require more room than
bonding pair of e-. They experience less
attraction from nuclear charge than a bonding
pair that is between two nuclei. They tend to
compress angles between bonding pairs.
Molecular geometry shows the geometry arrangement of
the atomic nuclei in relation to each other.
When lone pair of e- are present, e- geometry and
molecular geometry are different.
All of these show tetrahedral e- geometry;
however, the molecular geometry is
different in all.
VSEPR Notation
A = central atom
 X = terminal atoms
 E = lone pair of e
AX4
AX3E
AX2E2
We are going to go through all possibilities for:
number of e- groups
e- geometry
molecular geometry
VSEPR notation
bond angles
examples of each
If gone when going over, some examples are as
follows. However, VSEPR notation and bond
angles are not shown.
Determine the complete geometry and notation for:
[ICl4]-1
Determine the complete geometry and notation for:
SO2
When there is more than one central atom, consider the
geometry and notation around each separately.
Determine the complete geometry and notation for each
central atom in:
CH3 NCO
Hybridization is the
mixing of native
atomic orbitals to
form special orbitals
for bonding.
Example: CH4 shows
sp3 hybridization.
4 new orbitals are formed
from 1 (2s) orbital and
3(2p) orbitals. They form
hybrid orbitals with
When put
identical shape.
together they
form tetrahedral
shape.
sp2 hybridization
Shown in the
molecule C2H4
around each
carbon. One (2s)
and two (2p)
orbitals
hybridize to
form 3
equivalent
orbitals in
trigonal planar
orientation.
sp hybridization
shown in the
carbon of CO2, it
has one (2s) and
one (2p) orbital
hybridized to form
2 equivalent
orbitals. The
molecule becomes
linear.
O=C=O
When bonds form, there is an overlapping of
the orbitals between the 2 nuclei. One pair
of e- share the area centered alone a line
running between 2 nuclei. This bond is called
a sigma bond (s)
A double bond consists of one sigma and bond pi bond.
The remaining 2p orbitals are in a plane
perpendicular to the other bonds. They will bend
and overlap to form a pi bond (p) which surround
the s bond both above and below the plane of the
s bond.
Imagine the s bond as a hot dog and the p bond as the bun
around it.
Labeling the bonds
consists of noting
the type of bond and
the orbitals that
overlap.
C2H4
This molecule contains:
one s bond C (sp2) – C (sp2)
four s bonds C (sp2) – H (1s)
one p bond C (2p) – C (2p)
A triple bond consists of one s bond and two p
bonds. The two p bonds should be viewed as one
above and below the s bond, the other on either
side of the s bond.
Localized p bond is a bond which the e- are associated
totally with 2 atoms.
Delocalized p bonds are bonds with the e- involved
with several atoms held in the same plane. There will
be resonant structures.
Molecular Orbitals (MO Theory)
Overlap of 2 orbitals in a molecule create:
1. Constructive combination bonding MO
Concentration of e- exist between two nuclei
Lower energy
More stable!
2. Destructive combination antibonding MO
Concentration of e- exist on opposite sides of 2 nuclei
Higher energy
Bond order = ½ (# of bonding e- - # of antibonding e-)
Magnetic Properties

Diamagnetic elements have all e- in pairs,
therefore all individual magnetic properties
resulting from electrical spin is cancelled.
Diamagnetic elements are repelled by magnetic fields so they will
weigh slightly less in a magnetic field.

Paramagnetic elements have unpaired e-,
therefore the individual magnetic properties
resulting from electrical spin is not cancelled.
There is an induced magnetic field due to the
spin of the unpaired e-.
Paramagnetic elements are attracted by a magnetic field so they
will weigh slightly more in a magnetic field.