I II III

Molecular Geometry

(p. 232 – 236)

Ch. 8 – Molecular Structure

A. VSEPR Theory

Valence Shell Electron Pair Repulsion Theory

Electron pairs orient themselves in order to minimize repulsive forces

A. VSEPR Theory

Types of e- Pairs Bonding pairs – form bonds Lone pairs – nonbonding e-

Total e- pairs– bonding + lone pairs

Lone pairs repel

more strongly than bonding

pairs!!!

A. VSEPR Theory Lone pairs reduce the bond angle

between atoms

Bond AngleBond Angle

Draw the Lewis Diagram Tally up e- pairs on central atom (bonds + lone pairs)

double/triple bonds = ONE pair Shape is determined by the # of bonding pairs and

lone pairs

Know the 13 common shapes & their bond angles!

B. Determining Molecular Shape

C. Common Molecular Shapes # 1

2 total

2 bond

0 lone

LINEAR180°

BeH2

→ Electronic Geometry = linear

Hybridization = sp

3 total

3 bond

0 lone

TRIGONAL PLANAR

120°

BF3

C. Common Molecular Shapes # 2

→ Electronic Geometry = trigonal planar

Hybridization = sp2

C. Common Molecular Shapes # 33 total

2 bond

1 lone

BENT

<120°

NO21-

→ Electronic Geometry = trigonal planar

Hybridization = sp2

4 total

4 bond

0 lone

TETRAHEDRAL

109.5°

CH4

C. Common Molecular Shapes # 4

→ Electronic Geometry = tetrahedral

Hybridization = sp3

4 total

3 bond

1 lone

TRIGONAL PYRAMIDAL

107°

NCl3

C. Common Molecular Shapes # 5

→ Electronic Geometry = tetrahedral

Hybridization = sp3

<109.5°

4 total

2 bond

2 lone

BENT

104.5°

H2O

C. Common Molecular Shapes # 6

→ Electronic Geometry = tetrahedral

Hybridization = sp3

<109.5°

5 total

5 bond

0 lone

TRIGONAL BIPYRAMIDAL

120°/90°

PI5

C. Common Molecular Shapes # 7

→ Electronic Geometry = trigonal bipyramidal

Hybridization = sp3d

5 total

4 bond

1 lone

SEESAW

<120°/<90°

SF4

C. Common Molecular Shapes # 8

→ Electronic Geometry = trigonal bipyramidal

Hybridization = sp3d

5 total

3 bond

2 lone

T-SHAPE

<90°

ClF3

C. Common Molecular Shapes # 9

→ Electronic Geometry = trigonal bipyramidal

Hybridization = sp3d

5 total

2 bond

3 lone

LINEAR

180°

I31-

C. Common Molecular Shapes # 10

→ Electronic Geometry = trigonal bipyramidal

Hybridization = sp3d

6 total

6 bond

0 lone

OCTAHEDRAL

90°

SH6

C. Common Molecular Shapes # 11

→ Electronic Geometry = octahedral

Hybridization = sp3d2

6 total

5 bond

1 lone

SQUARE PYRAMIDAL

<90°

IF5

C. Common Molecular Shapes # 12

→ Electronic Geometry = octahedral

Hybridization = sp3d2

6 total

4 bond

2 lone

SQUARE PLANAR

90°

KrF4

C. Common Molecular Shapes # 13

→ Electronic Geometry = octahedral

Hybridization = sp3d2

SeO3

3 total

3 bond

0 lone

D. ExamplesO

O Se O

E.G. = TRIGONAL PLANARM.G. = TRIGONAL PLANAR

120°Hybridization = sp2

AsH3

4 total

3 bond

1 lone E.G. = TETRAHEDRALM.G. = TRIGONAL

PYRAMIDAL

107° (<109.5°)

H As HH

D. Examples

Hybridization = sp3

E. Hybridization

Provides information about molecular bonding and molecular shape

Several atomic orbitals mix to form same total of equivalent hybrid orbitals

E. Hybridization

Carbon is common example (orbital diagram)

One of 2s electrons is promoted to 2p 4 identical orbitals form sp3 hybridization

E. Hybridization Other types of hybridization

BeH2 forms

AlCl3 forms

SiF4 forms

KrF4 forms

SF4 forms

Remember the superscript is the orbital, not e-

configuration!

exceptions

sp

sp2

sp3

d2sp3 or sp3d2

dsp3 or sp3d

F. Hybridization Example Compare shapes and hybrid orbitals:

PF3 PF5

E.G. Tetrahedral Trigonal bipyramidal

M.G. Trigonal pyramidal Trigonal bipyramidal

HYB sp3 dsp3