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Chapter 4
Molecular Geometry and Bonding Theories
Examples
Dr.Harbi
Valence Shell Electron Pair Repulsion (VSEPR) Theory
• based on idea that regions of electron density in valence shell of central atom will be distributed in space such that electrostatic repulsions are minimized
• places regions of electron density as far apart as possible
• produces molecular geometry
Steps in Predicting Molecular Geometry
• draw Lewis structure of substance• count regions of electron density on
central atom• draw electron pair shape• derive and draw molecular geometry
Regions of Electron Density
• single covalent bond• double covalent bond• triple covalent bond• lone pair• unpaired electron
# Regions Shape
2 linear
180°
# Regions Shape
2
3
linear
trigonal planar
180°
120°
# Regions Shape
2
3
linear
trigonal planar
4 tetrahedral
180°
120°
109.5°
5 trigonal bypyramidal90°
120°
5 trigonal bypyramidal
6 octahedral
90°
90°
120°
Central Atoms Having Less than an Octet• Relatively rare.• Molecules with less than an octet are typical for
compounds of Groups 1A, 2A, and 3A.• Most typical example is BF3.
• Formal charges indicate that the Lewis structure with an incomplete octet is more important than the ones with double bonds.
Exceptions to the Octet Rule
Summary of VSEPR Molecular ShapesSummary of VSEPR Molecular Shapes
e-pairs Notation Name of VSEPR shape Examples2 AX2 Linear HgCl2 , ZnI2 , CS2 , CO2
3 AX3 Trigonal planar BF3 , GaI3
AX2E Non-linear (Bent) SO2 , SnCl2
4 AX4 Tetrahedral CCl4 , CH4 , BF4-
AX3E (Trigonal) Pyramidal NH3 , OH3-
AX2E2 Non-Linear (Bent) H2O , SeCl2
5 AX5 Trigonal bipyramidal PCl5 , PF5
AX4E Distorted tetrahedral (see-sawed)
TeCl4 , SF4
AX3E2 T-Shaped ClF3 , BrF3
AX2E3 Linear I3- , ICl2
-
6 AX6 Octahedral SF6 , PF6-
AX5E Square Pyramidal IF5 , BrF5
AX4E2 Square Planar ICl4- , BrF4
-
Examples
Determine the electron-pair (Domain) and molecular geometries of each of the following. Draw and name each.
Beryllium Chloride
Beryllium Chloride
BeCl2
Beryllium Chloride
BeCl2
1. Lewis structure
Beryllium Chloride
BeCl2
1. Lewis structure
Cl Be Cl
Beryllium Chloride
BeCl2
1. Lewis structure
Cl Be Cl
2. Count regions of electron density on central atom
Beryllium Chloride
BeCl2
1. Lewis structure
Cl Be Cl
2. Count regions of electron density on central atom 2
Beryllium Chloride
BeCl2
1. Lewis structure
Cl Be Cl
2. Count regions of electron density on central atom 2
3. Draw and name electron-pair shape
Cl Be Cl
linear
Beryllium Chloride
BeCl2
3. Draw and name electron-pair shape
Cl Be Cl
linear
3. Derive and name molecular shape
Cl Be Cl
linear
Carbon Dioxide
Carbon Dioxide
CO2
Carbon Dioxide
CO2
O C O
Carbon Dioxide
CO2
O C O
2 regions
Carbon Dioxide
CO2
O C O
2 regions
Electron-pair shape, linear
O C O
Carbon Dioxide
CO2
O C O
2 regions
Electron-pair shape, linear
O C O
Molecular shape, linear
O C O
Aluminum Bromide
Aluminum BromideAlBr3
Aluminum BromideAlBr3
Al
Br
Br Br
Aluminum BromideAlBr3
Al
Br
Br Br
3 regions
Aluminum BromideAlBr3
Al
Br
Br Br
3 regionsElectron-pair shapetrigonal planar
Al
Br
Br Br
Aluminum BromideAlBr3
Al
Br
Br Br
3 regionsElectron-pair shapetrigonal planar
Al
Br
Br Br
Molecular shapetrigonal planar
Al
Br
Br Br
Nitrite Ion
Nitrite Ion
NO2–
Nitrite Ion
NO2–
O N O
–
Nitrite Ion
NO2–
O N O
–
3 regions
Nitrite Ion
NO2–
O N O
–
3 regions
Electron-pair shapetrigonal planar
NO O
–
Nitrite Ion
NO2–
O N O
–
3 regions
Electron-pair shapetrigonal planar
NO O
–
Nitrite Ion
NO2–
O N O
–
3 regions
Electron-pair shapetrigonal planar
NO O
–Molecular shape bent
NO O
–
Carbon Tetrabromide
Carbon TetrabromideCBr4
Carbon TetrabromideCBr4
C
Br
Br Br
Br
Carbon TetrabromideCBr4
C
Br
Br Br
Br
4 regions
Carbon TetrabromideCBr4
C
Br
Br Br
Br
4 regions
Electron-pair shapetetrahedral
C
Br BrBr
Br
Carbon TetrabromideCBr4
C
Br
Br Br
Br
4 regions
Electron-pair shapetetrahedral
C
Br BrBr
Br
Molecular shapetetrahedral
Arsine
ArsineAsH3
ArsineAsH3
As
H
H H
ArsineAsH3
As
H
H H
4 regionselectron-pair shape, tetrahedral
ArsineAsH3
As
H
H H
4 regionselectron-pair shape, tetrahedral
As
HH
H
ArsineAsH3
As
H
H H
4 regionselectron-pair shape, tetrahedral
As
HH
H
molecular shapetrigonal pyramidor tripod
ArsineAsH3
As
H
H H
4 regionselectron-pair shape, tetrahedral
As
HH
H
molecular shapetrigonal pyramidor tripod
AsH
HH
WaterH2O
WaterH2O
O
HH
WaterH2O
O
HH
4 regionselectron-pair shapetetrahedral
WaterH2O
O
HH
4 regionselectron-pair shapetetrahedral
O
HH
WaterH2O
O
HH
4 regionselectron-pair shapetetrahedral
O
HH
molecular shapebent
WaterH2O
O
HH
4 regionselectron-pair shapetetrahedral
O
HH
molecular shapebent
OHH
Phosphorus Pentafluoride
Phosphorus PentafluoridePF5
PF
FF
FF
Phosphorus PentafluoridePF5
PF
FF
FF
5 regionselectron-pair shapetrigonal bipyramidal
F
F
F
F
F
P
Phosphorus PentafluoridePF5
PF
FF
FF
5 regionselectron-pair shapetrigonal bipyramidal
F
F
F
F
F
P
molecular shapetrigonal bipyramidal
Sulfur Tetrafluoride
Sulfur TetrafluorideSF4
Sulfur TetrafluorideSF4
SF F
FF
Sulfur TetrafluorideSF4
SF F
FF
5 regionstrigonal bipyramidal
Sulfur TetrafluorideSF4
SF F
FF
5 regionstrigonal bipyramidal
F
F
FF
S
Sulfur TetrafluorideSF4
SF F
FF
5 regionstrigonal bipyramidal
F
F
FF
S
F
F
FF
S
molecular shapedistorted tetrahedral
Sulfur TetrafluorideSF4
SF F
FF
5 regionstrigonal bipyramidal
F
F
FF
S
molecular shapesee saw
S
F
F F
F
Chlorine Trifluoride
Chlorine TrifluorideClF3
Chlorine TrifluorideClF3
F
FF
Cl
Chlorine TrifluorideClF3
F
FF
Cl 5 regionselectron-pair shapetrigonal bipyramidal
Chlorine TrifluorideClF3
F
FF
Cl 5 regionselectron-pair shapetrigonal bipyramidal
Cl
F
F
F
Chlorine TrifluorideClF3
F
FF
Cl 5 regionselectron-pair shapetrigonal bipyramidal
Cl
F
F
F
Chlorine TrifluorideClF3
F
FF
Cl 5 regionselectron-pair shapetrigonal bipyramidal
Cl
F
F
F
molecular shapeT-shape
Cl
F
F
F
Sulfur Hexafluoride
Sulfur HexafluorideSF6
Sulfur HexafluorideSF6
SF
FF
FF
F
Sulfur HexafluorideSF6
SF
FF
FF
F
6 regionselectron-pair shapeoctahedral
S
F
F
F
F
F
F
Sulfur HexafluorideSF6
SF
FF
FF
F
6 regionselectron-pair shapeoctahedral
S
F
F
F
F
F
F
molecular shapeoctahedral
Bromine Pentafluoride
Bromine PentafluorideBrF5
Bromine PentafluorideBrF5
BrF F
FF
F
Bromine PentafluorideBrF5
BrF F
FF
F
6 regionselectron-pair shapeoctahedral
Bromine PentafluorideBrF5
BrF F
FF
F
6 regionselectron-pair shapeoctahedral
Br
F
F
F
F
F
Bromine PentafluorideBrF5
BrF F
FF
F
6 regionselectron-pair shapeoctahedral
Br
F
F
F
F
F
Bromine PentafluorideBrF5
BrF F
FF
F
6 regionselectron-pair shapeoctahedral
Br
F
F
F
F
F
molecular shapesquare pyramidal
Br
F
F
F
F
F
Xenon Tetrafluoride
Xenon TetrafluorideXeF4
Xenon TetrafluorideXeF4
XeF F
FF
Xenon TetrafluorideXeF4
XeF F
FF
6 regionselectron-pair shapeoctahedral
Xenon TetrafluorideXeF4
XeF F
FF
6 regionselectron-pair shapeoctahedral
Xe
F
F
F
F
Xenon TetrafluorideXeF4
XeF F
FF
6 regionselectron-pair shapeoctahedral
Xe
F
F
F
F
Xenon TetrafluorideXeF4
XeF F
FF
6 regionselectron-pair shapeoctahedral
Xe
F
F
F
F
Xe
F
F
F
F
molecular shapesquare planar
Tribromide Ion Br3
–
Tribromide Ion Br3
–
Br
BrBr
Tribromide Ion Br3
–
Br
BrBr 5 regionselectron-pair shapetrigonal bipyramidal
Tribromide Ion Br3
–
Br
BrBr 5 regionselectron-pair shapetrigonal bipyramidal
Br
Br
Br
Tribromide Ion Br3
–
Br
BrBr 5 regionselectron-pair shapetrigonal bipyramidal
Br
Br
Br
Tribromide Ion Br3
–
Br
BrBr 5 regionselectron-pair shapetrigonal bipyramidal
Br
Br
Br
molecular shapelinear
Br
Br
Br
Polarity of Molecules
• molecules in which dipole moments of the bonds do not cancel are polar molecules
• molecules that do not contain polar bonds or in which all dipole moments cancel are non-polar molecules
CO2 vs H2O
CO OO
H H
CO2 vs H2O
CO OO
H H
+–
+ +
––
CO2 vs H2O
CO OO
H H
+–
+ +
––
CO2 vs H2O
CO OO
H H
+–
+ +
––
0
CO2 vs H2O
CO OO
H H
+–
+ +
––
0
CO2 vs H2O
CO O
O
H H
+
–
+ +
––
0
y
x
y
x
CO2 vs H2O
CO O
O
H H
+
–
+ +
––
y
x
y
x
CO2 vs H2O
CO OO
H H
+ –
+ +
––
nonpolar polar
Study and Know
9.2 Polarity of Molecules
VSEPR Theory only explains molecular shapes
says nothing about bonding in molecules
Enter Valence Bond (VB) Theory
atoms share electron pairs by allowing their atomic orbitals to overlap
+
H H
+
H H
bond
+
H H
bond
1sE
H
+
H H
bond
1s
E
H
H
+
F F
F2
+
F F
F2
bond
1s
2s
2pE
F
1s
2s
2p
F
E
F
Methane
CH4
1s
2s
2p
E
C
Methane
CH4
1s
2s
2p
E
C
H H
Methane
CH4
1s
2s
2p
E
C
H H
H+
Methane
CH4
1s
2s
2p
E
C
H H
H+
H–
Methane
CH4
1s
2s
2p
E
C
H H
H+
H–
C
H
H
H
H
90°
90°
Methane
CH4
C
H
HH
H
109.5°
Tetrahedral Geometry 4 Identical Bonds
Problem and Solution
C must have 4 identical orbitals in valence shell for bonding
solution: hybridization
Methane
CH4
1s
2s
2p
E
Methane
CH4
1s
2s
2p
E
1s
2s 2p
E
Methane
CH4
1s
2s
2p
E
1s
2s 2p
E
Methane
CH4
1s
2s
2p
E
1s
2s 2p
E
Methane
CH4
1s
2s
2p
E
1s
Esp3
– ++
+
2p2s
– ++
+
=2p2s
an sp3 hybrid orbital
4 identical sp3 hybrid orbitals
4 identical sp3 hybrid orbitals
tetrahedral geometry
4 identical sp3 hybrid orbitals
tetrahedral geometry
4 identical sp3 hybrid orbitals
tetrahedral geometry
Methane
CH4
1s
2s
2p
E
1s
Esp3
H H H H
Hybridization vs Shape (e– pair)
• sp linear• sp2 trigonal planar• sp3 tetrahedral• sp3d trigonal bipyramidal• sp3d2 octahedral
Predict the Hybridization of the Central Atom in tribromide ion
Predict the Hybridization of the Central Atom in tribromide ion
Br3–
Predict the Hybridization of the Central Atom in tribromide ion
Br3–
Br
BrBr 5 regionselectron-pair shapetrigonal bypyramidal
Predict the Hybridization of the Central Atom in tribromide ion
Br3–
Br
BrBr 5 regionselectron-pair shapetrigonal bypyramidal
sp3d
Predict the Hybridization of the Central Atom in carbon dioxide
CO2
Predict the Hybridization of the Central Atom in carbon dioxide
CO2
O C O
2 regions
Electron-pair shape, linear
Predict the Hybridization of the Central Atom in carbon dioxide
CO2
O C O
2 regions
Electron-pair shape, linear
sp
Predict the Hybridization of the Central Atom in aluminum bromide
Predict the Hybridization of the Central Atom in aluminum bromide
Al
Br
Br Br
3 regionsElectron-pair shapetrigonal planar
Predict the Hybridization of the Central Atom in aluminum bromide
Al
Br
Br Br
3 regionsElectron-pair shapetrigonal planar
sp2
Predict the Hybridization of the Central Atom in xenon tetrafluoride
Predict the Hybridization of the Central Atom in xenon tetrafluoride
XeF F
FF
6 regionselectron-pair shapeoctahedral
Predict the Hybridization of the Central Atom in xenon tetrafluoride
XeF F
FF
6 regionselectron-pair shapeoctahedral
sp3d2
Consider Ethylene, C2H4
Consider Ethylene, C2H4
C CH H
HH
Consider Ethylene, C2H4
C CH H
HH
3 regionstrigonal planar
Consider Ethylene, C2H4
C CH H
HH
3 regionstrigonal planar
sp2
Consider Ethylene, C2H4
C CH H
HH
3 regionstrigonal planar
sp2
1s
2s
2p
E
1s
2s
2p
E
1s
2s 2p
E
1s
2s
2p
E
1s
sp22p
E
sp2
sp2
sp2 2p
sp2
sp2
sp2
2p
bond framework
bond
bond
Consider Acetylene, C2H2
C C HH
Consider Acetylene, C2H2
C C HH
2 regionslinear
Consider Acetylene, C2H2
C C HH
2 regionslinearsp
Consider Acetylene, C2H2
C C HH
2 regionslinearsp
1s
2s
2p
E
1s
2s 2p
E
1s
2s
2p
E
1s
sp 2p
E
sp sp
2p
2p
bond framework
bonds
bonds
Generally
• single bond is a bond• double bond consists of 1 and 1
bond• triple bond consists of 1 and 2
bonds
Molecular Orbital (MO) Theory
when atoms combine to form molecules, atomic orbitals overlap and are then combined to form molecular orbitals
orbitals are conserved
a molecular orbital is an orbital associated with more than 1 nucleus
like any other orbital, an MO can hold 2 electrons
consider hydrogen atoms bonding to form H2
+
H H
add
subtract
add
subtract
bonding
antibonding
add
subtract
bonding
antibonding
*1s
1s
1s 1s
1s
*1s
H HH2
E E
1s 1s
1s
*1s
H HH2
E E
1s 1s
1s
*1s
H HH2
E E
1s 1s
1s
*1s
H HH2
E E
1s 1s
1s
*1s
H HH2
E E
(1s ) 2
1s 1s
1s
*1s
H HH2
E E
(1s ) 2
total spin = 0
• Diamagnetic: slightly repelled by a magnetic field
total spin = 0• paramagnetic: attracted to a
magnetic fiels
total spin not 0• Bond Order = 1/2 (bonding e– –
antibonding e–)
1s 1s
1s
*1s
H HH2
E E
(1s ) 2
total spin = 0diamagnetic
1s 1s
1s
*1s
H HH2
E E
BO = 1/2 ( 2 – 0) = 1
Consider He2
1s 1s
1s
*1s
He HeHe2
E E
1s 1s
1s
*1s
He HeHe2
E E
1s 1s
1s
*1s
He HeHe2
E E
(1s ) 2 ( *1s ) 2
1s 1s
1s
*1s
He HeHe2
E E
diamagnetic
1s 1s
1s
*1s
He HeHe2
E E
BO = 1/2 ( 2 – 2 ) = 0
Combination of p Atomic Orbitals
2p 2p
subtract
add
bonding MO
antibonding MOsubtract
add
bonding MO
antibonding MO *2p
2p
subtract
add
2p 2p
subtract
add
antibonding MO
bonding MO
subtract
add
2p
*2p
subtract
add
2p
*2p
subtract
add
Consider Li2
2s 2s
2s
*2s
Li LiLi2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
Li LiLi2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
Be BeBe2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
Be BeBe2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
B BB2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
B BB2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
C CC2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
N NN2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
O OO2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
F FF2
E E
2p 2p
*2p
2p
2p
*2p
2s 2s
2s
*2s
Ne NeNe2
E E
2p 2p
*2p
2p
2p
*2p