Review Chapter 10:
Theories of Bonding &
Structure
Chemistry: The Molecular Nature of Matter, 6th edition
By Jesperson, Brady, & Hyslop
Chapter 10 Concepts
 VESPR theory
 Predict molecular geometry & overall dipole moment
 Valence Bond Theory
 Identify & draw hybridization of orbitals at central atom
 Predict molecular geometry & overall dipole moment
 Identify & draw σ and π bonds
 Molecular Orbital Theory
 Draw MO Energy Diagrams to identify
 Bond Order
 Number of Unpaired Electrons
2
Memorize
Linear
Trigonal Planar
or
Planar Triangular
Trigonal Bipyramidal
Tetrahedral
Octahedral
Memorize
Trigonal
Pyramidal
T-shaped
Bent
Square
Pyramid
Seesaw or
Distorted
Tetrahedron
Square
Planar
Determining 3-D VESPR Stuctures
1. Draw Lewis Structure of Molecule
– Don't need to compute formal charge
– If several resonance structures exist, pick only one
2. Count electron pair domains
– Lone pairs and bond pairs around central atom
– Multiple bonds count as one set (or one effective pair)
3. Arrange electron pair domains to minimize repulsions
• Lone pairs
– Require more space than bonding pairs
– May slightly distort bond angles from those predicted.
– In trigonal bipyramid lone pairs are equatorial
– In octahedron lone pairs are axial
4. Name molecular structure by position of atoms—only bonding
electrons
Polarity
If symmetrical polar bonds around a central atom then
they cancel and there is no overall dipole moment.
Molecule is usually polar if
– All atoms attached to central atom are NOT same, OR
– There are one or more lone pairs on central atom
EXCEPT:
Valence Bond Theory
Valence Bond Theory
Individual atoms, each have their own orbitals and orbitals overlap to form bonds. Extent
of overlap of atomic orbitals is related to bond strength
Hybridization = mixing atomic orbitals
sp: Linear
sp3d: Trigonal
Bipyramidal
sp2: Planar
Triangular
sp3: Tetrahedral
sp3d2: Octahedral
Valence Bond Theory
1) Draw lewis dot structure
1) How many lone pairs & bonded atoms will repel one another? That is the
number of hybrid orbitals needed
2: sp
3: sp2 4: sp3 5: sp3d
6: sp3d2
2) Convert the needed number of atomic orbitals into hybridized orbitals.
1) Fill in valence electrons. Remember that any p orbitals will be close
enough in energy that they both hybrid & remaining p orbitals will fill half
way with electrons before they pair.
1) Draw hybrid orbitals equally spaced around the central atom:
a) Form σ bonds using hybrid orbitals with one electron
b) Hybrid orbitals with two electrons are likely lone pairs
c) If any lone electrons are in p orbitals π bonds will form
2) Describe molecular geometry around central atom(s).
Valence Bond Theory: Example N2
:NN:
p
E
p
sp
s
AO of N
• Lone pair and atom bonded to
Nitrogen will repel each other.
• Therefore, need to hybridize 2 orbitals
• One hybrid orbital with one electron
will participate in a σ bond with the
other nitrogen
• The other hybrid orbital contains a
lone pair
• 2 p orbitals each have 1 electron so
form 2 π bonds to the other nitrogen
Hybrid & AO of N
Molecular Orbital Theory
Molecular Orbital Theory
Views molecule as collection of positively charged nuclei having a set of molecular
orbitals that are filled with electrons (similar to filling atomic orbitals with electrons).
Doesn't worry about how atoms come together to form molecule
(number of bonding e – ) - (number of antibonding e – )
Bond order =
2 electrons/bond
Molecular Orbital Theory
Li2  N2
2p Lower in energy than 2p
O2, F2 and Higher 2p Lower in
energy than 2p
Can ignore filled 1s bonding & antibonding and focus on valence electrons
Molecular Orbital Theory: Diagrams
σ*
π*
p
π
E
σ
σ*
s
AO of one atom
σ
AO of second atom
Problem
Set A
1. For the following molecules:
a.
b.
c.
d.
e.
AsF5
Draw a lewis dot structure.
Determine the molecular geometry at each central atom.
Identify the bond angles.
Identify all polar bonds: δ+ / δAssess the polarity of the molecule & indicate the overall
dipole moment if one exists
AsF3
ICl2-
SeO2
GaH3
SiO4-4
TeF6
13
Problem
Set B
2.
3.
4.
5.
What is the hybridization of oxygen in OCl2?
For the species and XeF4O, determine the following:
a. electron domain geometry (geometry including non-bonding
pairs)
b. molecular geometry
c. Hybridization around central atom
d. Polarity
How many  and  bonds are there in CH2CHCHCH2, and what is
the hybridization around the carbon atoms?
Draw & list the bonding orbitals for HCN.
14
Problem
Set C
6. What is the MO Energy Diagram for B2? How many
unpaired electrons does B2 have?
6. What is the bond order & number of unpaired electrons
in O2 , O2+ , and O2- ?
6. Draw the MO Energy Diagram for BN.
15
Problem
Set A
16
Problem
Set A
17
Problem
Set A
18
Problem
Set B
2.
sp3
3.
XeF4O: octahedral, square pyramid, sp3d2, polar
3.
9, 2, sp2
3.
HCN: C will be create a σ bond to H and N with sp2 hybridized
orbitals and use 2 p orbitals to participate in 2 π bonds with N. N
will participate in the σ bond with C with an sp2 hybridized orbital,
the other will hold the N lone pair, and then N will use 2 p orbitals
to π bond with C.
19
Problem
Set C
B2
BN
σ*
σ*
6. MO B2:
unpaired e- = 2
7. O2: BO = 2
unpaired e- = 2
O2+: BO = 5/2 unpaired e- = 1
O2- : BO = 3/2 unpaired e- = 1
8. MO BN:
π*
π*
σ
σ
π
π
σ*
σ*
σ
σ
20
More Practice Problems:
Analyze the following compounds:
1. Draw the lewis dot structure
2. Determine the Geometry using VESPR theory
3. Determine the hybridization at any central atoms using VB Theory
4. Draw & Describe bonding in VB terms: ie # of sigma vs pi bonds
H2S
SO2
H2C=C=CH2
HCOCl