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 Geometry
Linear
Trigonal Planar
V-shaped
Tetrahedral
Trigonal Pyramidal
Trigonal Bipyramidal
Formula= AX2
Formula = AX3
Formula = : AX2
Formula = AX4
Formula = : AX3
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: SO42O
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) SO427) PH3
8) SO3