VSEPR Theory – Introduction
What Is VSEPR?
The Valence Shell Electron Pair Repulsion...theory:
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is used to PREDICT MOLECULAR ______________
is based on the number of regions of high electron density around a ___________________ atom.
can be used to predict structures of molecules or ions that contain only _____________________by minimizing the electrostatic
_______________________between the regions of high electron density.
can also be used to predict structures of molecules or ions that contain multiple bonds or unpaired electrons.
does fail in some cases.
What steps need to be followed in order to apply the VSEPR theory?
1. Draw the Lewis structure for the molecule or ion.
2. Count the total number of regions of high electron density (i.e. the number of bonding and non-bonding lone electron pairs) around the
central atom.
o Double and triple bonds count as ___________ REGION OF HIGH ELECTRON DENSITY.
o An unpaired electron counts as ONE REGION OF HIGH ELECTRON DENSITY.
o For molecules or ions that have resonance structures, you may use any one of the resonance structures.
Some GUIDELINES to follow when applying VSEPR Theory:
*Keep in mind that there are some exceptions to the following...these are good “rules of thumb”.
1. Hydrogen only ever forms ___________ bond.
2. Carbon, Nitrogen, Oxygen and Fluorine always adhere to the _________________ RULE...they are “unable” to expand their octet.
*The OCTET RULE “Violators”:
3. Beryllium usually only forms ___________bonds...and yes, beryllium can form covalent bonds even though it is a metal.
4. Boron usually only forms _______________bonds.
5. Non-metals in period three and beyond ________ expand their octet(as a result of “available” ____-orbitals).
*(e.g. Sulfur, phosphorus, chlorine , bromine, iodine, xenon...can all have more than 8 electrons in their valence shell.)
Bond
Pairs
Lone
Pairs
General
Formula
Molecular
Geometry
(Name of
Shape)
Hybridization
Electron Domain
Geometry
Total e- pairs on
central atom
SHAPES OF MOLECULES: PART 1
Bond
Angle
e.g.
2
Linear
Bel2
3
Trigonal Planar
BCl3
SO2
4
Tetrahedral
CBr4
NCl3
OF2
Lewis Structure
3-D Shape Sketch
Bond
Pairs
Lone
Pairs
General
Formula
Molecular
Geometry
(Name of
Shape)
Hybridization
Electron Domain
Geometry
Total e- pairs on
central atom
SHAPES OF MOLECULES: PART II
Bond
Angle
e.g.
PCl5
5
Trigonal Bipyramidal
SCl4
ICl3
I3-
Lewis Structure
3-D Shape Sketch
SF6
6
Octahedral
BrF5
XeF4
*Multiple bonding in VSEPR models:
 Treat DOUBLE and TRIPLE bonds as if they were SINGLE bonds when applying VSEPR theory.
Examples: Draw Lewis Structures and predict the shape of the following:
a) CO2
d) PO43g) NO3j) methanoic acid, HCOOH
b) HCN
e) ethene, C2H4
h) CS2
k) methanol, CH3OH
2c) CO3
f) ethyne, C2H2
i) methanal, HCHO
l) SO42-
m) carbon monoxide, CO
n) ozone, O3
*o) benzene ring, C6H6
*m) NO2+
*n) NO2
*o) NO2-