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

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Skeleton Diagrams of Molecules

A

B

B B

B

N

H

H HB

AB BAB B

A B

A

B

B BB

A

B

B B

BB

A

BB

BB

BBA

BB

BB

B ABBB

B