What determines molecular shape?

Bond angles: angle formed between two adjacent bonds on the same atom

e.g. CCl4

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

bond angle: ?

Lewis Structures

What determines molecular shapes?

=> tell us how atoms are physically connected

No information regarding the actual 3-D structure of molecules

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

Repulsion of valence electrons => largest possible separation of atoms

Valence-Shell Electron-Pair Repulsion Model

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

Different ways of depicting 3-D structure

bonds in plane of paper

bond in front of the paper plane

bond behind of the paper plane

"Ball and Stick" "Spacefilling"

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

nonbonding pair

bonding pair

Types of Electron Domains: ● nonbonding (or "lone") electrons● single OR double OR triple bonding

electrons

Lewis structures show number of electron domains

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

=> Bonding AND non-bonding electron pairs take up space

Molecular shape depends on electron domain geometry

Lewis Structures tell us …

● where bonds (bonding electron pairs) are

● the location of nonbonding electrons

Bonding AND non-bonding electron pairs take up space

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

} around the central atom

Possible Electron Domain Geometries:

Linear

Trigonal Planar Tetrahedral

TrigonalBipyramidal

Octahedral

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

180o

120o 109.5o

120o

90o

90o

90o

4 electron domains around central atom=> electron domain geometry: Tetrahedral

nonbonding pairbonding pair

Lewis structures → electron domain geometry → molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

3 non-bonding + 1 bonding electron domain

Lewis structures → electron domain geometry → molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

S FF

4 electron domains around central atom=> electron domain geometry: Tetrahedral

Lewis structures → electron domain geometry → molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

3 electron domains around central atom=> electron domain geometry: Trigonal planar

B

F

F F

Lewis structures → electron domain geometry → molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

2 electron domains around central atom=> electron domain geometry: Linear

CO O

Lewis structures → electron domain geometry → molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

3 electron domains around central atom=> electron domain geometry: Trigonal planar

N OO

4 electron domains:=> electron domain geometry

Tetrahedral

3 bonds, 1 nonbonding pair:=> molecular geometry

Trigonal pyramidal

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

Lewis structures → electron domain geometry → molecular geometry

Molecular Geometry depends on how many of the electron domains are actually bonds

Bond angles can be distorted:

109.5 o

107 o

104.5 o

● nonbonding electron pairs occupy more volume than bonding pairs

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

Bond angles can be distorted

● multiple bonds occupy a larger volume than single bonds

125.3 o

125.3 o

111.4 o

lone pairs => triple bonds => double bonds => single bondsVolume Volume

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

Elements from the 3rd period onward..

● have d -orbitals● can have an expanded valence shell● may have more than 4 electron domains surrounding them

e.g. phosphorous:

P: [Ne] 3s2 3p3 3s 3p 3d

"expanded" valence shell

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

Equatorial bond

Axial bond

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

TeF6

# electrondomains

electrondomain geometry

molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

Te

F

F

F

F

FF

H3O+

+

# electrondomains

electrondomain geometry

molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

NO2

# electrondomains

electrondomain geometry

molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

N OO

SO3

# electrondomains

electrondomain geometry

molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

SCl2

# electrondomains

electrondomain geometry

molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

SCl Cl

SbI5

# electrondomains

electrondomain geometry

molecular geometry

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories

SbI

II

I

I

The VESPR model can be extended to larger moleculese.g. glycine :

Electron-domain geometry:

predicted bond angles: ?

? ?

?

Chapter 9: Molecular Geometry and Bonding TheoriesChapter 9: Molecular Geometry and Bonding Theories