I II
III

A. VSEPR Theory
 V alence Shell Electron Pair
Repulsion Theory
 Electron pairs orient themselves so that valence electrons are as far apart as possible

A. VSEPR Theory
 Types of e Pairs

Bonding pairs - form bonds

Lone pairs - nonbonding e -
Lone pairs repel more strongly than bonding pairs!!!

A. VSEPR Theory
 Lone pairs reduce the bond angle between atoms.
Bond Angle

B. Determining Molecular Shape
 Draw the Lewis Diagram.
 Count up e pairs on central atom.
 double/triple bonds = ONE pair
 Shape is determined by the # of bonding pairs and lone pairs.
Know the 8 common shapes
& their bond angles!

C. Common Molecular Shapes
2 total electron pairs
*2 bonding pairs
*0 lone pairs
BeH
2
Note: Beryllium does not follow the octet rule. Beryllium is complete with 4 valence electrons
180 °

C. Common Molecular Shapes
3 total electron pairs
*3 bonding pairs
*0 lone pairs
BF
3 TRIGONAL PLANAR
Note: Boron is also an exception to the octet rule. Boron is complete with
6 valence electrons
120 °

C. Common Molecular Shapes
3 total pairs
*2 bonding pairs
*1 lone pair
SO
2 BENT
<120 °

C. Common Molecular Shapes
4 total pairs
*4 bonding pairs
*0 lone pairs
CH
4
109.5
°

C. Common Molecular Shapes
4 total pairs
*3 bonding pairs
*1 lone pair
NH
3
TRIGONAL PYRAMIDAL
107 °

C. Common Molecular Shapes
4 total pairs
*2 bonding pairs
*2 lone pairs
H
2
O
104.5
°

C. Common Molecular Shapes
5 total pairs
*5 bonding pairs
*0 lone
PCl
5
TRIGONAL
BIPYRAMIDAL
120 °/90°

C. Common Molecular Shapes
6 total pairs
*6 bonding pairs
*0 lone pairs
SF
6
90 °

D. Examples n
PF
3
4 total
3 bond
1 lone
F P F
F
TRIGONAL
PYRAMIDAL
107 °

D. Examples n
CO
2
2 total
2 bonding pairs
0 lone
O C O
LINEAR
180 °

I II
III

Molecular Polarity
• Polar Molecule : Molecule that has a partially positive end and a partially negative end. (It has electrical poles)
• There is an uneven distribution of electrons in the molecule

A. Dipole Moment
 Direction of the polar bond in a molecule.
 Arrow points toward the more electronegative atom.

+ H Cl

-

B. Determining Molecular Polarity
 Depends on:
 dipole moments
 molecular shape

B. Determining Molecular Polarity
 Nonpolar Molecules

Dipole moments are symmetrical and cancel out.
F
BF
3
B
F
F

B. Determining Molecular Polarity
 Polar Molecules

Dipole moments are asymmetrical and don’t cancel .
.. ..
O
H
2
O
H H net dipole moment

B. Determining Molecular Polarity
 Polar molecules have...
 asymmetrical shape (lone pairs) or
 asymmetrical atoms (attached atoms are different)

B. Determining Molecular
Polarity
 Nonpolar Molecules have…

No lone pairs

All attached atoms are the same