Molecular Geometry

Lecture 7.4

Molecular Geometry = the 3-D arrangement of atoms in a molecule

- This arrangement affects the physical and chemical properties of a molecule

- The geometry that the polyatomic molecule assumes minimizes the valence shell electron repulsions

- The study of molecular geometry is called the Valence Shell Electron-Pair Repulsion model

VSEPR Model!!

VSEPR Model

1) All bonds from the central atom are called

a) always consider a multiple bond as a

2) If there are any lone pairs of e^- on the central atom, they are also

Have to draw the correct Lewis dot structure to determine!!

Ex:

BeCl₂

C₂H₄

H₂O

VSEPR Model

3) We will use the following terminology to help us describe the e^- pair arrangement and molecular geometry

A = central atom

B = bonded e^- cloud

E = lone pair e^- cloud

2 Charge Clouds =

1) AB₂

Ex: BeCl₂

A) Charge clouds = 2 (2 bonded) , AB₂

B) Geometry =

C) Bond angle =

2 Charge Clouds =

2) AB₁E₁

Ex: CO

A) Charge clouds = 2 (1 bonded, 1 lone) , AB₁E₁

B) Geometry =

C) Bond angle =

3 Charge Clouds =

1) AB₃

Ex: BF₃

A) Charge clouds = 3 (3 bonded) , AB₃

B) Geometry =

C) Bond angle =

3 Charge Clouds =

2) AB₂E₁

Ex: SO₂

A) Charge clouds = 3 (2 bonded, 1 lone) , AB₂E₁

B) Geometry =

C) Bond angle =

4 Charge Clouds =

1) AB₄

Ex: CH₄

A) Charge clouds = 4 (4 bonded) , AB₄

B) Geometry =

C) Bond angle =

4 Charge Clouds =

2) AB₃E₁

Ex: NH₃

A) Charge clouds = 4 (3 bonded, 1 lone) , AB₃E₁

B) Geometry =

C) Bond angle =

4 Charge Clouds = Tetrahedral distribution of e^-

3) AB₂E₂

Ex: H₂O

A) Charge clouds = 4 (2 bonded, 2 lone) , AB₂E₂

B) Geometry = bent/v-shaped

C) Bond angle = <109.5°

5 Charge Clouds =

1) AB₅

Ex: PCl₅

A) Charge clouds = 5 (5 bonded) , AB₅

B) Geometry =

C) Bond angle =

expanded valence!

5 Charge Clouds =

2) AB₄E₁

Ex: SF₄

A) Charge clouds = 5 (4 bonded, 1 lone) , AB₄E₁

B) Geometry =

C) Bond angle =

5 Charge Clouds =

3) AB₃E₂

Ex: BrF₃

A) Charge clouds = 5 (3 bonded, 2 lone) , AB₃E₂

B) Geometry =

C) Bond angle =

6 Charge Clouds =

1) AB₆

Ex: SF₆

A) Charge clouds = 6 (6 bonded) , AB₆

B) Geometry =

C) Bond angle =

6 Charge Clouds =

2) AB₅E₁

Ex: ClF₅

A) Charge clouds = 6 (5 bonded, 1 lone) , AB₅E₁

B) Geometry =

C) Bond angle =

6 Charge Clouds =

3) AB₄E₂

Ex: XeF₄

A) Charge clouds = 6 (4 bonded, 2 lone) , AB₄E₂

B) Geometry =

C) Bond angle =