Molecular Geometry( Textbook: page383-392)

Valence Electron Pair Repulsion

The arrangement of atoms within a given molecule.

Is based on simple electrostatic repulsions of electron pairs

Assumption

Electrons in chemical bonds( single, double, or triple) and unshared electron pairs are negative centers that repel each other

Molecular GeometryLinear Formula= AX2

Trigonal Planar Formula = AX3

V-shaped Formula = : AX2

Tetrahedral Formula = AX4

Trigonal Pyramidal Formula = : AX3

Trigonal Bipyramidal Formula = AX5

. .

T-shaped Formula = : A X3

See Saw Formula = : AX4

Octahedral Formula = AX6

Note: A –represents the central atom

X – represents the attached atom

( AX2)

2 Bonding pairs

0 lone pairs

Ex: BeCl2

Cl– Be—Cl

1800

Linear

Ex: CO2

O=C=O

1800

AX3

3 Bonding Pairs

0 lone pairs

Ex:BCl3

Cl

B 120

Cl Cl

Trigonal Planar

.. : AX2

2 Bonding pairs

2 lone pairs

Ex: H20

H– O –H since lone pair is more electronegative than the

bonding pairs it tends to push the bonding pairs closer together, thereby decreasing the angle between them

O H H v-shaped (less than 1090)

Tetrahedral ( AX4)

4 bonding pairs

0 lone pairs

Ex: CH4

H 109

H C H H

Ex: SO42-

O O S O O

Trigonal Pyramidal :AX3

3 bonding pairs

One lone pair

Ex: NH3

109.50

N

H H H

Exercises

Write the Lewis structure and predict the molecular geometry of the following using VSPER Model

1) OF2

2) PF3

3) CS2

4) NSF

5) SF4

6) SO42-

7) PH3

8) SO3