1. Theories of Bonding and Structure
CHAPTER 10
Chemistry: The Molecular Nature of Matter, 6th edition
By Jesperson, Brady, & Hyslop

2. 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

3. Basic Molecular Geometries
Molecular Geometry
Basic Molecular Geometries
Linear
3 atoms
Trigonal Planar or
Planar Triangular
4 atoms
Trigonal Bipyramidal
6 atoms
Tetrahedral:
5 atoms
Octahedral:
7 atoms
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

4. Valence Shell Electron Pair Repulsion Model
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

5. Valence Shell Electron Pair Repulsion Model
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

6. 6 bonding bonding domains
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

7. When Lone Pairs or Multiple Bonds Present
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

8. Electrons that are Bonding & Not Bonding
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

9. 3 2 1 VESPR 3 atoms or lone pairs Number of Bonding Domains
Number of Nonbonding Domains 1
Structure
Molecular Shape
Planar Triangular
(e.g. BCl3)
All bond angles 120
Nonlinear
Bent or V-shaped
(e.g. SnCl2)
Bond <120
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

10. 4 3 2 1 2 VESPR 4 atoms or lone pairs Number of Bonding Domains
Number of Nonbonding Domains 1 2
Structure
Molecular Shape
Tetrahedron
(e.g. CH4)
All bond angles 
Trigonal pyramidal
(e.g. NH3)
Bond angle less than 109.5
Nonlinear, bent
(e.g. H2O)
Bond angle
less than109.5
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

11. Two atoms in axial position 90 to atoms in equatorial plane
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

12. 5 4 1 VESPR 5 atoms or lone pairs Number of Bonding Domains
Number of Nonbonding Domains 1
Structure
Molecular Shape
Trigonal bipyramid
(e.g. PF5)
Ax-eq bond angles 90
Eq-eq 120
Distorted Tetrahedron, or Seesaw
(e.g. SF4)
Ax-eq bond angles < 90
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

13. Lone pair takes up more space Goes in equatorial plane
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

14. 3 2 2 3 VESPR 5 atoms or lone pairs Number of Bonding Domains
Number of Nonbonding Domains 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

15. 6 5 1 VESPR 6 atoms or lone pairs Number of Bonding Domains
Number of Nonbonding Domains 1
Structure
Molecular Shape
Octahedron
(e.g. SF6)
Square Pyramid
(e.g. BrF5)
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

16. 4 2 VESPR 6 atoms or lone pairs Number of Bonding Domains
Number of Nonbonding Domains 2
Structure
Molecular Shape
Square planar
(e.g. XeF4)
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

17. Determining 3-D Structures
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
Name molecular structure by position of atoms—only bonding electrons
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

18. 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

19. Molecular Shape & Polarity
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
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

20. Symmetrical Nonpolar Molecules
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

21. Symmetrical Nonpolar Molecules
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

22. Molecule is usually polar if
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

23. Water and ammonia both have non-bonding domains
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

24. Exception to these general rules for identifying polar molecules:
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

25. For the following molecules:
Problem
Set A
For the following molecules:
Draw a lewis dot structure.
Determine the molecular geometry at each central atom.
Identify the bond angles.
Identify all polar bonds: δ+ / δ-
Assess the polarity of the molecule & indicate the overall dipole moment if one exists
AsF5 AsF3 SeO2 GaH3
ICl2- SiO TeF6