Chapter 9: Molecular Geometry
VSEPR Theory and Lewis Dot Diagrams:
VSEPRTotal
Electron
Covalent
Sites and Compound
Geometry
Hydrogen
Hydrogen
fluoride
Oxygen
Molecular
Nonbonding
Lewis
Bonding
Shape
Polar/Nonpolar
Sites on
Diagram Sites
and
Molecule
central atom
Angle
Total
Electron
Covalent
Sites and Compound
Geometry
Nitrogen
Carbon
Dioxide
Beryllium
Hydride
Boron
Fluoride
Molecular
Nonbonding
Lewis
Bonding
Shape
Polar/Nonpolar
Sites on
Diagram Sites
and
Molecule
central atom
Angle
Total
Electron
Covalent
Sites and Compound
Geometry
NO2-1
Methane
Ammonia
Water
Molecular
Nonbonding
Lewis
Bonding
Shape
Polar/Nonpolar
Sites on
Diagram Sites
and
Molecule
central atom
Angle
Total
Electron
Covalent
Sites and Compound
Geometry
Phosphorous
Pentachloride
Sulfur Tetra
Chloride
Chlorine
Trifluoride
Sulfur
Hexafluoride
Molecular
Nonbonding
Lewis
Bonding
Shape
Polar/Nonpolar
Sites on
Diagram Sites
and
Molecule
central atom
Angle
Total
Electron
Covalent
Sites and Compound
Geometry
Molecular
Nonbonding
Lewis
Bonding
Shape
Polar/Nonpolar
Sites on
Diagram Sites
and
Molecule
central atom
Angle
Xenon
Bromine
Pentafluoride
Bent vs. Linear. Discuss.
H2 O
Polarity
Polar Bonds vs. Polar Molecules
CO2
Dipole Moments
HF
BeH2
NH3
AlCl3
CCl4
CHCl3
Zero Dipole Moment:
Resonance Structures
Draw SO3
Draw AsO3-
Draw CO3-2
Draw SO2
Geometry Chart Summary and Trends
# of
#bonding
attachments
sites
# non
bonding
sites
Electron geometry
Molecule geometry
Hybridization
Polarity
(assume
bonded
atoms are
the same)
Angle
Covalent Bonding: Hybrid Orbitals
Covalent Bonding- Electrons are shared between two nonmetals. A molecule with a covalent bond is
called a ________________________.
Bonds are made by the overlap between 2 unpaired valence electrons.
Ex. H2
H
H
Making Bonds- Release
Energy and Create Stability!
Configuration:
Shape:
Bond!
HYBRIDIZATION- The mixing of atomic orbitals attempts to explain observed shapes in polyatomic
molecules and the formation of bonds.
Ex. BeH2
H electron configurationCheck for unpaired eBe electron configuration-
Draw filling model for valence shell electrons
_______
2s
______ ______ ______
2p
Because there are no unpaired electrons, Be is not likely to bond. In order to bond, electrons must be
_____________________.
_______
2s
______ ______
2p
______
_______
______ ______
2s
______
2p
Now there are 2 unpaired electrons available for bonding
***When this happens, s and p orbitals combine or mix or hybridize to make 2
identical orbitals called ________ orbitals. ***
These new sp orbitals align to minimize repulsions and therefore determines the shape of the molecule.
Draw BeH2
Geometries
Linear
Bonding/Nonbonding Sites
Hybridization
Trigonal Planar
Tetrahedral
Trigonal Bipyramidal
Octahedral
Hybrid orbitals are used to explain why geometric shapes occur!
Steps in predicting the hybrid orbitals used by an atom in bonding:
1. Draw the Lewis structure
2. Determine the electron pair geometry using the VSEPR model
3. Specify the hybrid orbitals needed to accommodate the electron pairs in the geometric arrangement
Ex. NH3
Ex. H2S
Ex. CO2
AP Bonding Free Response Questions
1. Answer the following questions using principles of chemical bonding and molecular structure.
a. Consider the carbon dioxide molecule, CO2 , and the carbonate ion, CO32-.
i. Draw the complete Lewis electron-dot structure for each species and identify their molecular
geometry.
ii. Account for the fact that the carbon-oxygen bond length in CO32- is greater than the carbonoxygen bond length in CO2.
b. Consider the molecules CF4 and SF4.
i.
Draw the complete Lewis electron-dot structure for each molecule.
ii. In terms of molecular geometry, account for the fact that the CF4 molecule is nonpolar,
whereas the SF4 molecule is polar.
2. Consider the molecules PF3 and PF5.
a) Draw the Lewis electron-dot structures for PF3 and PF5 and predict the hybridization, bond angles,
and molecular geometry of each.
b) Is the PF3 molecular polar, or is it nonpolar? Explain.
c) On the basis of bonding principles, predict whether each of the following compounds exists. In
each case, explain your prediction.
(i) NF5
(ii) AsF5