Theories of Bonding
and Structure
CHAPTER 10
Chemistry: The Molecular Nature of Matter, 6th edition
By Jesperson, Brady, & Hyslop
CHAPTER 10: Bonding & Structure
Learning Objectives
 VESPR theory:
 Determine molecular geometry based on molecular formula
and/or lewis dot structures.
 Effect of bonded atoms & non-bonded electrons on geometry
 Molecular polarity & overall dipole moment
 Assess overall dipole moment of a molecule
 Identify polar and non-polar molecules
 Valence Bond Theory
 Hybridized orbitals
 Multiple bonds
 Sigma vs pi orbitals
 Molecular Orbital Theory
 Draw & label molecular orbital energy diagrams
 Bonding & antibonding orbitals
 Predict relative stability of molecules based on MO diagrams
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Molecular
Geometry
Basic Molecular Geometries
Linear
3 atoms
Trigonal Planar
or
Planar Triangular
Trigonal Bipyramidal
6 atoms
4 atoms
Tetrahedral:
5 atoms
Octahedral:
7 atoms
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Molecular Nature of Matter, 6E
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VESPR
Definition
Valence Shell Electron Pair Repulsion Model
Electron pairs (or groups of electron pairs) in the valence shell of an atom
repel each other and will position themselves so that they are far apart as
possible, thereby minimizing the repulsions.
Electron pairs can either be lone pairs or bonding pairs.
Tetrahedral arrangement
of electron pairs
Bent geometry
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
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VESPR
Definition
Valence Shell Electron Pair Repulsion Model
Electron pairs (or groups of electron pairs) in the valence shell of an atom
repel each other and will position themselves so that they are far apart as
possible, thereby minimizing the repulsions.
Text uses “electron domain” to describe electron pairs:
Bonding domain: contains electrons that are shared between
two atoms. So electrons involved in single, double, or triple are
part of the same bonding domain.
Nonbonding Domain: Valence electrons associated with one
atom, such as a lone pair, or a unpaired electron.
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
Basic Examples
2 bonding
domains
3 bonding
domains
5 bonding domains
4 bonding
domains
6 bonding bonding
domains
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
When Lone Pairs or Multiple Bonds Present
Including lone pairs:
• Take up more space around central atom
• Effect overall geometry
• Counted as nonbonded electron domains
Including multiple bonds (double and triple)
• For purposes of determining geometry focus on the number
of atoms bonded together rather then the number of bonds
in between them: ie, treat like a single bond.
• Treat as single electron bonding domain
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
Electrons that are Bonding & Not Bonding
Bonding Electrons
– More oval in shape
– Electron density focused
between two positive nuclei.
Nonbonding Electrons
– More bell or balloon shaped
– Take up more space
– Electron density only has
positive nuclei at one end
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
3 atoms or lone pairs
Number of
Bonding
Domains
Number of
Nonbonding
Domains
3
0
Planar Triangular
(e.g. BCl3)
All bond angles 120
1
Nonlinear
Bent or V-shaped
(e.g. SnCl2)
Bond <120
2
Structure
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
Molecular Shape
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VESPR
Number of
Bonding
Domains
4
4 atoms or lone pairs
Number of
Nonbonding
Domains
Structure
Molecular Shape
Tetrahedron
(e.g. CH4)
All bond angles 109.5 
0
Trigonal
pyramidal
3
(e.g. NH3)
Bond angle
less than 109.5
1
Nonlinear, bent
2
2
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
(e.g. H2O)
Bond angle
less than109.5
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VESPR
5 atoms or lone pairs
Trigonal Bipyramidal
• Two atoms in axial position
– 90 to atoms in equatorial
plane
• Three atoms in equatorial
position
– 120 bond angle to atoms
in axial position
– More room here
– Substitute here first
90
120
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
5 atoms or lone pairs
Number of
Bonding
Domains
Number of
Nonbonding
Domains
5
0
4
Structure
Molecular Shape
Trigonal bipyramid
(e.g. PF5)
Ax-eq bond angles 90
Eq-eq 120
Distorted
Tetrahedron, or
Seesaw
(e.g. SF4)
1
Ax-eq bond angles < 90
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
•
•
•
•
5 atoms or lone pairs
Lone pair takes up more space
Goes in equatorial plane
Pushes bonding pairs out of way
Result: distorted tetrahedron
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
5 atoms or lone pairs
Number of Number of
Bonding
Nonbonding
Domains Domains
3
2
2
3
Structure
Molecular Shape
T-shape
(e.g. ClF3)
Bond angles 90
Linear
(e.g. I3–)
Bond angles 180
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
6 atoms or lone pairs
Number of Number of
Bonding
Nonbonding
Domains
Domains
6
0
5
1
Structure
Molecular Shape
Octahedron
(e.g. SF6)
Square Pyramid
(e.g. BrF5)
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
6 atoms or lone pairs
Number of Number of
Bonding
Nonbonding
Domains
Domains
4
Structure
Molecular Shape
Square planar
(e.g. XeF4)
2
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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VESPR
Determining 3-D Structures
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
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Molecular
Polarity
Polar Molecules
• Have net dipole moment
– Negative end
– Positive end
• Polar molecules attract each other.
– Positive end of polar molecule attracted to
negative end of next molecule.
– Strength of this attraction depends on
molecule's dipole moment
– Dipole moment can be determined
experimentally
• Polarity of molecule can be predicted by taking
vector sum of bond dipoles
• Bond dipoles are usually shown as crossed
arrows, where arrowhead indicates negative end
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Molecular
Polarity
Molecular Shape & Polarity
• Many physical properties (melting and boiling points)
affected by molecular polarity
• For molecule to be polar:
– Must have polar bonds
• Many molecules with polar
bonds are nonpolar
- Possible because certain
arrangements of bond
dipoles cancel
- For molecules with more
than two atoms, must
consider the combined
effects of all polar bonds
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
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Molecular
Polarity
Symmetrical Nonpolar Molecules
• Symmetrical molecules
– Nonpolar because bond dipoles cancel
• All five shapes are symmetrical when all domains attached to
them are composed of identical atoms
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Molecular
Polarity
Symmetrical Nonpolar Molecules
Cancellation of Bond Dipoles In Symmetrical Trigonal Bipyramidal and
Octahedral Molecules
•
•
•
All electron pairs around central atom are bonding pairs and
All terminal groups (atoms) are same
The individual bond dipoles cancel
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Molecular
Polarity
Polar Molecules
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
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Molecular
Polarity
Polar Molecules
 Water and ammonia both have non-bonding domains
 Bond dipoles do not cancel
 Molecules are polar
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Molecular
Polarity
Polar Molecules: Execption
Exception to these general rules for identifying polar
molecules:
Nonbonding domains (lone pairs) are symmetrically
placed around central atom
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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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
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