6/20/2015 one point quiz one quiz per table, list everyone’s name agree on an answer you have...
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04/18/23
One Point Quiz
One quiz per table, list everyone’s name Agree on an answer You have two minutes
04/18/23
Unknown Dues Dates
Unknown AFriday, Week 5 Unknown BFriday, Week 7 Unknown C Friday, Week 9 Unknown D Friday, Week 10
VSEPRValence Shell Electron Pair Repulsion
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
04/18/23
Bonding Theories
Ionic Model Skeleton Diagrams Lewis Dot Diagrams Molecular Orbital Theory Orbital Hybridization Valence Bond Theory Valence Shell Electron Pair Repulsion
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VSEPRValence Shell Electron Pair Repulsion
Allows the prediction of molecular geometry• An extension of the “groups of electrons”
(effective electron pair) concept• Involves sp and dsp types of hybridizations• The central atom may or may not obey the
octet rule.
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To Determine
Molecular Geometry
Count the number of valence electrons. Place a pair of electrons between the atoms bound
together. Each non-central (terminal) atom is given electrons to
fulfill its inert gas configuration. Any additional electron pairs become lone (unshared)
electrons pairs on the central atom. The geometry is determined by the number of
bonding and unshared pairs of electrons on the central atom.
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Consider the Possible Combinations
Atoms Bound to the Central Atom
1 2 3 4 5 6
0
1
2
3
Nu
mb
er o
fL
on
e E
lect
ron
Pai
rs
What is the preferred geometryfor the blocks shown in blue?
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Zero Lone Pairs of ElectronsAround the Central Atom
Number of AtomsBound to theCentral Atom
Arrangement Geometry Example
1 A B linear H2
2 AB B linear BeH2
3B
AB B
trigonalplanar
BF3
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Zero Lone Pairs of ElectronsAround the Central Atom
Number of AtomsBound to theCentral Atom
Arrangement Geometry Example
4 A
B
B BB
tetrahedral CH4
5 A
B
B B
BB
trigonalbipyramidal PCl5
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Zero Lone Pairs of ElectronsAround the Central Atom
Number of AtomsBound to theCentral Atom
Arrangement Geometry Example
6 A
BB
BB
BB
octahedral SF6
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AB Type Moleculeswith Unshared Pairs of Electrons
1 A B linear CO
A B2 linear O2
3 A B linear HF
Arrangement Geometry ExampleNumber of LoneElectron Pairs on
Central Atom
Molecular Models
Look at the various molecular modelsThe blue sphere represents an atomThe “paddle” represents a pair of electrons
Only atoms can be “seen”.
What is the shape of each molecule?
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AB2 Type Molecules
with Unshared Pairs of Electrons
1 AB B
bent120º) O3
2 AB B H2Obent109º)
3 A
B
B
linear XeF2
Arrangement Geometry ExampleNumber of LoneElectron Pairs on
Central Atom
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AB3 Type Molecules
with Unshared Pairs of Electrons
1 AB B
B
trigonalpyramidal NH3
A
B
B
B
2 T-shaped ClF3
Arrangement Geometry ExampleNumber of LoneElectron Pairs on
Central Atom
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AB4 Type Molecules
with Unshared Pairs of Electrons
A
BB
BB1
sawhorse,see-saw TeCl4
ABBB
B2squareplanar XeF4
Arrangement Geometry ExampleNumber of LoneElectron Pairs on
Central Atom
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AB5 Type Molecules
with Unshared Pairs of Electrons
A
BB
BB
Bsquare
pyramidal1 IF5
Arrangement Geometry ExampleNumber of LoneElectron Pairs on
Central Atom
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Lone Electron Pair Position
The lone pairs always occur in the equatorial plane.• Maximizes the angular separation between
lone pairs and other electron pairs.
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Summary of Observed Geometries
1
linear
linear
linear
linear
2
linear
bent(120º)
bent(109º)
linear
3trigonalplanar
trigonalpyramidal
T-shaped
4
tetrahedral
sawhorse,see-saw
squareplanar
5trigonal
bipyramidal
squarepyramidal
6
octahedral
Atoms Bound to the Central Atom
0
1
2
3Nu
mb
er
of
Lo
ne
Ele
ctro
n P
air
s
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Skeleton Diagrams of Molecules
N
H
H H
OH H
AB B A
B
B BB
A
B
B B
BB
AB B
A B
A B
A B
º
B
AB B
AB B
A
B
B
A
B
B
BA
BB
BB
AB B
B