1. Contents 10-1 Lewis Theory: An Overview
10-2 Covalent Bonding: An Introduction
10-3 Polar Covalent Bonds
10-4 Writing Lewis Structures
10-5 Resonance
10-6 Exceptions to the Octet Rule
10-7 The Shapes of Molecules
10-8 Bond Order and Bond Lengths
10-9 Bond Energies
Focus On Molecules in Space: Measuring Bond Lengths
General Chemistry: Chapter 10
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2. 10-1 Lewis Theory: An Overview
Chemistry 140 Fall 2002
10-1 Lewis Theory: An Overview
Valence e- play a fundamental role in chemical bonding.
e- transfer leads to ionic bonds.
Sharing of e- leads to covalent bonds.
e- are transferred or shared to give each atom a noble gas configuration
the octet.
General Chemistry: Chapter 10
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3. General Chemistry: Chapter 10
Lewis Symbols
A chemical symbol represents the nucleus and the core e-.
Dots around the symbol represent valence e-. • Si • • • N •• • P As Sb Bi •• Al • Se Ar I
General Chemistry: Chapter 10
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4. General Chemistry: Chapter 10
Chemistry 140 Fall 2002
EXAMPLE 10-2
Writing Lewis Structures of Ionic Compounds. Write Lewis structures for the following compounds: (a) BaO; (b) MgCl2 ; (c) aluminum oxide. Ba • O •• •• O Ba 2+ 2-
BaO
Note the use of the “fishhook” arrow to denote a single electron movement. A “double headed” arrow means that two electrons move.
Binary ionic compounds.
Note the types of arrows used to move electrons – fishhooks for single e-.
Write the Lewis symbol for each atom Determine how many e- each atom must gain or lose.
Use multiples of one or both ions to balance the number of electrons.
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5. General Chemistry: Chapter 10
EXAMPLE 10-2 Mg • Cl •• •• Cl Mg 2+ - 2
MgCl2
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6. 10-2 Covalent Bonding: An Introduction
General Chemistry: Chapter 10
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7. Coordinate Covalent Bonds
Chemistry 140 Fall 2002
Coordinate Covalent Bonds N H + N •• H •• Cl - H Cl
Note double headed arrow for two electron movement
Note the “double headed” arrow showing that two electrons move.
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8. Multiple Covalent Bonds
Often, more than one pair of electrons must be shared
for an atom to attain an octet. • • • C O • ••
• • O • C O • •
• • •
• • •
• • • C O •• C O ••
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9. Multiple Covalent Bonds• • N • •• •• N • • N •• • • N • •• N ••
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10. General Chemistry: Chapter 10
Polar Covalent Bonds
Most chemical bonds fall between 100% ionic and 100% covalent.
In a polar covalent bond, electrons are not shared equally between two atom.
In such a bond, electrons are displaced toward the more nonmetallic element.
General Chemistry: Chapter 10
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11. General Chemistry: Chapter 10
Electronegativity: an atom’s ability to compete for electrons with other atoms to which it is bonded.
General Chemistry: Chapter 10
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12. Percent Ionic Character of a bond based on ∆EN
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13. Electrostatic potential map
There are methods that allow us to display the electron density distribution within molecules.
The Electrostatic Potential map is obtained by hypothetically probing an electron density surface with a positive point charge.
General Chemistry: Chapter 10
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14. 10-3 Polar Covalent Bonds and Electrostatic Potential Maps
We can map the electron density
throughout a molecule.
The electrostatic potential
is the work
done in moving the
unit of +ve charge
from one region of a
molecule to another.
General Chemistry: Chapter 10
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15. Polar Molecules

16. Learn how to apply
Valence Shell Electron Pair Repulsion, VSEPR, Theory to predict the shapes of molecules.
The three-dimensional shape of a molecule is important in determining its chemical behavior, particularly for biologically important molecules.

17. Applying VSEPR Theory Draw a plausible Lewis structure.
Determine the number of electron groups around the central atom and identify them as bond or lone pairs.
Establish the electron group geometry.
Determine the molecular geometry.
Multiple bonds count as one group of electrons.

18. Trigonal
Planar
Linear
Octahedral
Tetrahedral
Trigonal
Bipyramidal

19. Dipole Moments and Polarity:
In molecules containing atoms with different electronegativities, there is an unequal sharing of electron density.
In other words, a polar covalent bond is formed.

21. Dipole Moments and Polarity:
Dipoles are vector quantities that are additive to produce an overall molecular dipole moment.
For Diatomic molecules from atoms of different electronegativity there is always a dipole moment.

22. General Chemistry: Chapter 10
For polyatomic molecules the resultant dipole moment is a vector sum of the individual bond dipoles. As a result not all molecules with polar covalent bonds have a net molecular dipole.
General Chemistry: Chapter 10
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23. General Chemistry: Chapter 10
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25. General Chemistry: Chapter 10
Chemistry 140 Fall 2002
Dipole Moments
Ana electrical condenser (or capacitor) consists of a pair of electrodes separated by a medium that does not conduct electricity. When the field is off the molecules orient randomly. When the filed is on the molecules align with the field. The alignment can be detected.
General Chemistry: Chapter 10
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26. General Chemistry: Chapter 10
Chemistry 140 Fall 2002
Dipole Moments
HCl is a polar molecule
General Chemistry: Chapter 10
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27. Electrostatic potential map
There are methods that allow us to display the electron density distribution within molecules.
The Electrostatic Potential map is obtained by hypothetically probing an electron density surface with a positive point charge.
General Chemistry: Chapter 10
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28. 10-3 Polar Covalent Bonds and Electrostatic Potential Maps
We can map the electron density
throughout a molecule.
The electrostatic potential
is the work
done in moving the
unit of +ve charge
from one region of a
molecule to another.
General Chemistry: Chapter 10
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29. Polar Molecules

30. Bond Order and Bond Length
Single bond, order = 1
Double bond, order = 2
Bond Length
Distance between two nuclei
Higher bond order
Shorter bond
Stronger bond
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31. General Chemistry: Chapter 10
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32. General Chemistry: Chapter 10
Bond Energies
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33. General Chemistry: Chapter 10
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34. General Chemistry: Chapter 10
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35. General Chemistry: Chapter 10
A phase is a homogenous part of the system in
contact with other parts of the system but separated
From them by a well-defined boundary
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36. General Chemistry: Chapter 10
Intermolecular Forces: are attractive forces between molecules. These are the
forces primarily responsible for the bulk physical properties of matter, such as
boiling point.
Intramolecular Forces: are forces that hold molecules together (bonds). These
stabilize individual molecules.
Types of Intermolecular Forces:
• Ion-Ion interaction
• Ion-Dipole interaction
• Dipole-Dipole interaction
• Hydrogen-Bonding
• Ion-Induced dipole interaction
• Dipole-Induced dipole interaction
• Dispersion (induced dipole-induced dipole or van der Waals forces)
General Chemistry: Chapter 10
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37. General Chemistry: Chapter 10
Intermolecular Forces: are attractive forces between molecules. These are the
forces primarily responsible for the bulk physical properties of matter, such as
boiling point.
Intramolecular Forces: are forces that hold molecules together (bonds). These
stabilize individual molecules.
Types of Intermolecular Forces:
• Ion-Ion interaction
• Ion-Dipole interaction
• Dipole-Dipole interaction
• Hydrogen-Bonding
• Ion-Induced dipole interaction
• Dipole-Induced dipole interaction
• Dispersion (induced dipole-induced dipole or van der Waals forces)
General Chemistry: Chapter 10
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38. General Chemistry: Chapter 10
Ion-Ion interaction: The force of attraction between ions is described by Coulomb’s
law.
General Chemistry: Chapter 10
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39. General Chemistry: Chapter 10
Chemistry 140 Fall 2002
EXAMPLE 10-15
Calculating an Enthalpy of Reaction from Bond Energies. The reaction of methane (CH4) and chlorine produces a mixture of products called chloromethanes. One of these is monochloromethane, CH3Cl, used in the preparation of silicones. Calculate H for the reaction.
ΔHrxn =  ΔH(product bonds) - ΔH(reactant bonds)
=  ΔH bonds formed -  ΔH bonds broken
= -770 kJ/mol – (657 kJ/mol) = -113 kJ/mol
You can use bond energies in exactly the same way you can use enthalpies of formation. Enthalpy of formation is more accurately known and bond energy is usually an average, but it can be used effectively if formation data is unavailable.
General Chemistry: Chapter 10
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42. The Lewis Structure is a representation of a molecule that shows how the valence electrons are arranged among the atoms in the molecule.

43. 1. Skeletal structure; determine central and terminal atoms; low EN atoms central, O and H usually terminal. 2. Determine # of valence electrons. 3.Determine # of electrons needed for each atom to achieve octet. 4. # of electrons in step 3 minus # of electrons in step 2 will give you # of bonding electrons. 5. Place bonding electrons among atoms in the structure (connect atoms and use all of the bonding electrons; you may get more than one plausible structure).
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44. General Chemistry: Chapter 10
6. Did you use all of the valence electrons from step 2? If yes, you are done, go to step 8. if no, go to step 7.
7. Place the left over valence electrons
( from step 2) as non-bond pairs on the atoms for each atom to achieve octet ( exception, H must achieve duet).
8. Check if structure(s) are valid by determining the formal charges on the atoms.
General Chemistry: Chapter 10
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45. Writing Lewis Structures
All the valence e- of atoms must appear.
Usually, the e- are paired.
Usually, each atom requires an octet.
H only requires 2 e-.
Multiple bonds may be needed.
Readily formed by C, N, O, S, and P.
General Chemistry: Chapter 10

46. FC = #valence e- - #lone pair e- - #bond pair e-
Chemistry 140 Fall 2002
Formal Charge: The formal charge on an atom in a Lewis structure is the number of valence e- in the free atom minus the number of e- assigned to that atom in the Lewis structure.
FC = #valence e- - #lone pair e- - 1
#bond pair e- 2
Formal charges is a measure of the extent to which an atom
has gained or lost an electron in the process of forming a
covalent bond.
The formal charge on an atom in a Lewis structure is the number of valence e- in the free atom minus the number of e- assigned to that atom in the Lewis structure.

47. O≡N—O Sum of FC is the overall charge.
FC should be as small as possible.
Negative FC usually on most electronegative elements.
FC of same sign on adjacent atoms is unlikely. + ••
O≡N—O -

48. Exceptions to the Octet Rule
Chemistry 140 Fall 2002
Exceptions to the Octet Rule
Odd e- species.
N=O • •• •• •• H •• •
O—H
H—C—H H • ••
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49. Exceptions to the Octet Rule
Incomplete octets. •• B F - + •• B F - •• + •• F •• B •• F F •• •• •• •• ••

50. Exceptions to the Octet Rule
Expanded octets. S F •• •• P Cl •• •• Cl •• P •• •• Cl Cl •• •• •• •• ••

51. Learn how to apply
Valence Shell Electron Pair Repulsion, VSEPR, Theory to predict the shapes of molecules.
The three-dimensional shape of a molecule is important in determining its chemical behavior, particularly for biologically important molecules.

52. Valence Shell Electron Pair Repulsion VSEPR Theory
Chemistry 140 Fall 2002
Valence Shell Electron Pair Repulsion VSEPR Theory
Electron Pairs in the Valence Shell of the central atom Repel each other whether they are in chemical bonds (bond pairs) or unshared (lone pairs).
Electron pairs assume orientations about an atom to minimize repulsions. .. .. .. .. .. ..

53. General Chemistry: Chapter 10
Balloon Analogy
General Chemistry: Chapter 10
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54. Applying VSEPR Theory Draw a plausible Lewis structure.
Determine the number of electron groups around the central atom and identify them as bond or lone pairs.
Establish the electron group geometry.
Determine the molecular geometry.
Multiple bonds count as one group of electrons.

55. Trigonal
Planar
Linear
Octahedral
Tetrahedral
Trigonal
Bipyramidal

56. Methane, Ammonia and Water

57. Table 10.1 Molecular Geometry as a Function of Electron Group Geometry

63. Applying VSEPR Theory Draw a plausible Lewis structure.
Determine the number of e- groups and identify them as bond or lone pairs.
Establish the e- group geometry.
Determine the molecular geometry.
Multiple bonds count as one group of electrons.
More than one central atom can be handled individually.

64. General Chemistry: Chapter 10
Chemistry 140 Fall 2002
Dipole Moments
Ana electrical condenser (or capacitor) consists of a pair of electrodes separated by a medium that does not conduct electricity. When the field is off the molecules orient randomly. When the filed is on the molecules align with the field. The alignment can be detected.
General Chemistry: Chapter 10
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65. General Chemistry: Chapter 10
Chemistry 140 Fall 2002
Dipole Moments
HCl is a polar molecule
General Chemistry: Chapter 10
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66. General Chemistry: Chapter 10
The difference in electronegativity values between two atoms in a
bond (ΔEN) may be used to predict if a bond is:
a) non-polar, covalent b) polar, covalent c) ionic
For the following compounds predict whether the bond type is
a), b) or c) and justify your answer.(a bond is
considered to be ionic if ΔEN > 1.7). Find the melting point of these compounds from the library ('The Handbook of Chemistry and Physics')
and confirm whether the melting point agrees with the predicted bond type.
NCl3 AlCl3 SO3 KI CH4 CF4
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67. General Chemistry: Chapter 10
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68. General Chemistry: Chapter 10
Of the following compounds of sulfur, which, if any, do not possess a permanent dipole. Take the Pauling
electronegativity value for a lone pair = 3.7.
SF SF SF3− SF SF SF5− SF6
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69. Bond Order and Bond Length
Single bond, order = 1
Double bond, order = 2
Bond Length
Distance between two nuclei
Higher bond order
Shorter bond
Stronger bond
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70. General Chemistry: Chapter 10
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71. General Chemistry: Chapter 10
Bond Energies
General Chemistry: Chapter 10
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72. General Chemistry: Chapter 10
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73. General Chemistry: Chapter 10
Chemistry 140 Fall 2002
EXAMPLE 10-15
Calculating an Enthalpy of Reaction from Bond Energies. The reaction of methane (CH4) and chlorine produces a mixture of products called chloromethanes. One of these is monochloromethane, CH3Cl, used in the preparation of silicones. Calculate H for the reaction.
ΔHrxn =  ΔH(product bonds) - ΔH(reactant bonds)
=  ΔH bonds formed -  ΔH bonds broken
= -770 kJ/mol – (657 kJ/mol) = -113 kJ/mol
You can use bond energies in exactly the same way you can use enthalpies of formation. Enthalpy of formation is more accurately known and bond energy is usually an average, but it can be used effectively if formation data is unavailable.
General Chemistry: Chapter 10
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74. Focus on Molecules in Space: Measuring Bond Lengths
General Chemistry: Chapter 10
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75. End of Chapter Questions
Testing your decisions:
If you get an error or a nonsense result, then climb back to an intersection where you KNOW you were correct, and take another route. a b c c d? e
e?!# f
Answer
General Chemistry: Chapter 10
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