Theories of Bonding and Structure
CHAPTER 10
Chemistry: The Molecular Nature of Matter, 6th editionBy Jesperson, Brady, & Hyslop
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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
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Linear3 atoms
Trigonal Planaror
Planar Triangular
4 atoms
Tetrahedral:5 atoms
Trigonal Bipyramidal6 atoms
Octahedral:7 atoms
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VESPR Definition
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E http://chemistry-desk.blogspot.com/2011/05/prediction-of-shape-of-molecules-by.html
Valence Shell Electron Pair Repulsion ModelElectron 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 pairsBent geometry
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VESPR Definition
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Valence Shell Electron Pair Repulsion ModelElectron 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.
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VESPR Basic Examples
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
2 bonding domains
3 bonding domains
4 bonding domains
5 bonding domains
6 bonding bonding domains
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VESPR When Lone Pairs or Multiple Bonds Present
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
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
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VESPR Electrons that are Bonding & Not Bonding
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
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
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VESPR 3 atoms or lone pairs
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Number of Bonding Domains
3
2
Number of Nonbonding Domains
0
1
Molecular Shape
Planar Triangular(e.g. BCl3)All bond angles 120
NonlinearBent or V-shaped(e.g. SnCl2)
Bond <120
Structure
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VESPR 4 atoms or lone pairs
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Number of Bonding Domains
4
3
2
Number of Nonbonding Domains
0
1
2
Molecular Shape
Tetrahedron(e.g. CH4)All bond angles 109.5
Trigonal pyramidal(e.g. NH3)Bond angle less than 109.5
Nonlinear, bent(e.g. H2O)Bond angle less than109.5
Structure
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VESPR 5 atoms or lone pairs
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
90
120
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
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VESPR 5 atoms or lone pairs
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Number of Bonding Domains
5
4
Number of Nonbonding Domains
0
1
Molecular Shape
Trigonal bipyramid(e.g. PF5)Ax-eq bond angles 90Eq-eq 120
Distorted Tetrahedron, or Seesaw(e.g. SF4)Ax-eq bond angles < 90
Structure
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5 atoms or lone pairs
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
• Lone pair takes up more space• Goes in equatorial plane• Pushes bonding pairs out of way• Result: distorted tetrahedron
VESPR
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VESPR 5 atoms or lone pairs
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Number of Bonding Domains
3
2
Number of Nonbonding Domains
2
3
Molecular Shape
T-shape(e.g. ClF3)Bond angles 90
Linear(e.g. I3
–)Bond angles 180
Structure
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VESPR 6 atoms or lone pairs
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Number of Bonding Domains
6
5
Molecular Shape
Octahedron(e.g. SF6)
Square Pyramid(e.g. BrF5)
StructureNumber of Nonbonding Domains
0
1
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VESPR 6 atoms or lone pairs
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Number of Bonding Domains
4
Number of Nonbonding Domains
2
Molecular Shape
Square planar(e.g. XeF4)
Structure
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VESPR Determining 3-D Structures
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
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
Molecular Polarity Polar Molecules
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
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• 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
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Molecular Polarity Molecular Shape & Polarity
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6Ehttp://wps.prenhall.com/wps/media/objects/3081/3155729/blb0903.html
• 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
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Molecular Polarity Symmetrical Nonpolar Molecules
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
• Symmetrical molecules – Nonpolar because bond dipoles cancel
• All five shapes are symmetrical when all domains attached to them are composed of identical atoms
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Molecular Polarity Symmetrical Nonpolar Molecules
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
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
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Molecular Polarity Polar Molecules
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
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
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Molecular Polarity Polar Molecules
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Water and ammonia both have non-bonding domains Bond dipoles do not cancel Molecules are polar
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Molecular Polarity Polar Molecules: Execption
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Exception to these general rules for identifying polar molecules:
Nonbonding domains (lone pairs) are symmetrically placed around central atom
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ProblemSet A
1. For the following molecules: a. Draw a lewis dot structure.b. Determine the molecular geometry at each central atom.c. Identify the bond angles.d. Identify all polar bonds: δ+ / δ-e. Assess the polarity of the molecule & indicate the overall
dipole moment if one exists
AsF5 AsF3 SeO2
GaH3
ICl2- SiO4-4
TeF6
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