I II
III

YouTube
Video on VSPER Theory

Learning Objectives
 TLW predict molecular structure for molecules using Valence Shell Electron
Pair Repulsion (VSEPR) Theory (TEKS
7.E)

A. VSEPR Theory
1. V alence S hell E lectron P air R epulsion
Theory gives us a three-dimensional picture of atomic bonding that the
Electron Dot Structure does not.
2. Electron pairs orient themselves in order to minimize repulsive forces.

VSEPR:
3. Predicts three dimensional geometry of molecules.
4. The name tells you the theory:
5. Valence shell - outside electrons.
6. Electron Pair repulsion - electron pairs try to get as far away as possible.
7. Can determine the angles of bonds.

A. VSEPR Theory
Types of e Pairs
1. Bonding pairs - form bonds
2. 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
1. Draw the Lewis Diagram.
2. Tally up e pairs on central atom.
a. double/triple bonds = ONE pair
3. Shape is determined by the # of bonding pairs and lone pairs.
Know the 3 most common shapes
& their bond angles!

C. Common Molecular Shapes 1
2 total
2 bond
0 lone
BeH
2
180 °

Examples
 CO
2
2 total
2 bond
0 lone
O C O
LINEAR
180 °

C. Common Molecular Shapes 2
3 total
2 bond
1 lone
SO
2 BENT
<120 °

C. Common Molecular Shapes 3
3 total
3 bond
0 lone
BF
3
TRIGONAL PLANAR
120 °

C. Common Molecular Shapes 4
4 total
4 bond
0 lone
CH
4
109.5
°

C. Common Molecular Shapes 5
4 total
3 bond
1 lone
NH
3
TRIGONAL PYRAMIDAL
107 °

Examples
 PF
3
4 total
3 bond
1 lone
F P F
F
TRIGONAL
PYRAMIDAL
107 °

C. Common Molecular Shapes 6
4 total
2 bond
2 lone
H
2
O
104.5
°

C. Common Molecular Shapes 7
5 total
5 bond
0 lone
PCl
5
TRIGONAL
BIPYRAMIDAL
120 °/90°

C. Common Molecular Shapes 8
6 total
6 bond
0 lone
SF
6
90 °

Examples










 linear: BeH
2
, CO
2
, MgF
2
, I
3 bent (angular): SO
2
, H
2
O, H square planar: XeF
4
, IF
4
-
2
S, SF
2 trigonal planar : SO
3
, BF
3 square pyramidal: IF
5
, BrF
5 trigonal pyramidal: NH
3
, PF
3
, AsCl
3 trigonal bipyramidal: PF
5
, PCl
5
, AsF tetrahedral : CH
4
, CF
4
, SO
4
2-
5 octahedral: SF
6
, PF
6
, SiF
6
2seesaw: SF
4
T-shaped: ClF
3

D. Orbital Hybridization
 VSEPR Theory works well when accounting for molecular shapes, but doesn’t help describing the types of bonds formed.
 In hybridization, several atomic orbitals mix to form the same total number of equivalent hybrid orbitals
 YouTube video

D. Orbital Hybridization
 For Example ~ Methane (CH
4
)

C = 1s 2 2s 2 2p 2

H = 1s 1 (and there are four H atoms)

C re-configures its one 2s and three 2p orbitals into four sp 3 orbitals, which overlap the 1s orbitals of the 4 hydrogen atoms

Group Practice
 Molecular Geometry Construction
Game Revisited

E. One Other Note on Bonding
 Electronegativity determines bonding which contributes to the bond angle

Greater than 1.7  ionic bonds

0.3 – 1.7  polar covalent bonds

0 – 0.3  covalent
See handout for trends through periodic table

Electronegativities
•
Greater than 1.7
 ionic bonds
•
0.3 – 1.7
 polar covalent bonds
•
0 – 0.3
 covalent

Independent Practice
 Building 3-D Examples of Molecular
Geometry

VSEPR Marshmellow Lab
 VSEPR Exercise – 2