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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