Ch. 9: Molecular Geometry & VSEPR Theory
1. VSEPR theory enables us to predict the shape (molecular geometry) of molecules based on the
representative Lewis structure for each molecule. VSEPR stands for:
V- _________________________
P- _________________________
S- _________________________
R- _________________________
E- _________________________
2. VSEPR theory predicts the _______ ______________ of molecules based on the fact that there is
______________________ between the valence electrons surrounding the central atom of molecule.
a. Bonding electrons pairs (single/double/triple bonds) take up space in a molecule and
repel one another
b. Nonbonding electron pairs also take up ___________ space in a molecule and repel
electrons ___________ strongly than bonding electron pairs
c.
As a result of this repulsion, the atoms in a molecule space themselves out ______
__________ _________________ from one another as possible.
VSEPR  “The best arrangement of a given number of electron domains is the one
that minimizes the repulsions among them.”
3. Fill in the table below:
Name &
Formula
Lewis
structure
#
atoms
bonded
to
central
# nonbonding
electron
pairs
around
central
# of
domains
around
central
ABN type*
Molecular Shape
Polar (P)
or
Nonpolar
(NP)
Methane
CH4
Ammonia
NH3
Water
H2O
* Write the ABN formula for each of these molecules.
A= central atom, B= number of attached atoms, N= Number of nonbonding electron pairs.
The VSEPR chart (found in your reference sheets) lists possible shapes of molecules, based
on their Lewis structure and ABN type.
Be comfortable with interpreting this information…like you just did!
The website below is excellent for visualizing the 3D orientation of each different molecular
geometry or for building example molecules
Online Simulator: http://phet.colorado.edu/en/simulation/molecule-shapes
4. Polarity:

Polarity: physical property of a substance which results from an uneven distribution of
positive and negative charge in a molecule or chemical bond

Polar Bonds: We know (from chapter 8) that polar bonds result from having a significant
difference in the _____________________________ of the two bonding atoms


Molecular Polarity: When it comes to an entire molecule being polar, it must contain
polar bonds and be arranged in space 3-dimensionally so that there is an uneven
distribution of positive and negative charge (ie: the molecular geometry is important!!!)

a.
This results in one portion of the bond being partially negative (ϭ-) and the other
half being partially positive (ϭ+)
A molecule could contain polar bonds without the entire molecule being polar
Polar Molecules:

A polar molecule must contain polar bonds and have those polar bonds arranged in space
3-dimensionally (aka: the molecular geometry) so that one side of the molecule is partially
negative (ϭ-) and the other side is partially positive (ϭ+)

These molecules are considered to be ____________________________ in shape (most
often due to the presence of _______________________ electron pairs on the central
atom).

Polar molecules form opposite “poles” within the molecule: one positive, one negative
b.
Nonpolar Molecules:

These molecules are considered to be very __________________________ in shape
(“no poles”).

Either these molecules contain NO polar bonds, or any polar bonds it does contain are
“canceled” out by the 3D shaping of the molecule
Now You Try:
Molecule
ClO3–
CHO–
Lewis structure
# atoms
bonded
to
central
# nonbonding
electron
pairs
around
central
# of
domains
around
central
ABN type*
Molecular Shape
Polar (P)
or
Nonpolar
(NP)
VSEPR – Predicting Molecular Shapes
Directions: Fill in the table below by drawing the Lewis Structure of the molecule and determining its
ABN type and molecular shape
Molecule
CCl4
CO2
ClF3
XeBr2
Lewis structure
# atoms
bonded
to
central
# nonbonding
electron
pairs
around
central
# of
domains
around
central
ABN type*
Molecular Shape
Polar (P)
or
Nonpolar
(NP)
Molecule
IBr5
PH5
NO2–
XeF4
Lewis structure
# atoms
bonded
to
central
# nonbonding
electron
pairs
around
central
# of
domains
around
central
ABN type*
Molecular Shape
Polar (P)
or
Nonpolar
(NP)
Molecule
HCN
CHBr3
HCl
O3
I3–
Lewis structure
# atoms
bonded
to
central
# nonbonding
electron
pairs
around
central
# of
domains
around
central
ABN type*
Molecular Shape
Polar (P)
or
Nonpolar
(NP)