1. Chapter 11: Chemical Bonding I: Basic Concepts
Chemistry 140 Fall 2005
General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th Edition
Chapter 11: Chemical Bonding I: Basic Concepts
Philip Dutton
University of Windsor, Canada
N9B 3P4
Prentice-Hall © 2002
(modified 2003 by Dr. Paul Root and
2005 by Dr. David Tramontozzi)
Thermochemistry branch of chemistry concerned with heat effects accompanying chemical reactions.
Direct and indirect measurement of heat.
Answer practical questions: why is natural gas a better fuel than coal, and why do fats have higher energy value than carbohydrates and protiens.
Prentice-Hall © 2002
General Chemistry: Chapter 9

2. General Chemistry: Chapter 9
Contents
11-1 Lewis Theory: An Overview
11-2 Covalent Bonding: An Introduction
11-3 Polar Covalent Bonds
11-4 Writing Lewis Structures
11-5 Resonance
11-6 Exceptions to the Octet Rule
11-7 The Shapes of Molecules
11-8 Bond Order and Bond Lengths
11-9 Bond Energies
Focus on Polymers— Macromolecular Substances
Prentice-Hall © 2002
General Chemistry: Chapter 9

3. 11-1 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 RULE.
Prentice-Hall © 2002
General Chemistry: Chapter 9

4. General Chemistry: Chapter 9
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 • •• I •• Ar • • •• • • •• ••
Prentice-Hall © 2002
General Chemistry: Chapter 9

5. Lewis Structures for Ionic Compounds
Chemistry 140 Fall 2005
Lewis Structures for Ionic Compounds Ba • O •• 2+ •• 2-
BaO Ba •• O •• •• Mg • Cl •• 2+ •• -
MgCl2 Mg 2 •• Cl •• ••
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.
Prentice-Hall © 2002
General Chemistry: Chapter 9

6. General Chemistry: Chapter 9
Chemistry 140 Fall 2005
11-2 Covalent Bonding
Notice the octets of electrons attained by each atom through covalent bond formation.
One covalent bond represents two electrons – one being donated from each atom
Lone pairs are pairs of electrons not used in bonding – they play a role in molecular shape
Hydrogen is an exception since it only requires 2 electrons to fill its outer shell.
Prentice-Hall © 2002
General Chemistry: Chapter 9

7. Coordinate Covalent Bonds
Chemistry 140 Fall 2005
Coordinate Covalent Bonds
A covalent bond in which a single atom contributes both of the electrons to be shared N H + N •• H •• Cl - H Cl
Note double headed arrow for two electron movement
Coordinate covalent bond is a shared pair of electrons in which both electrons used for the bond come from one of the atoms.
Once formed a coordinate covalent bond is indistinguishable from a regular covalent bond.
Prentice-Hall © 2002
General Chemistry: Chapter 9

8. Multiple Covalent Bonds
Chemistry 140 Fall 2005
Multiple Covalent Bonds
Single covalent bond formation results in a situation where both oxygen and carbon do not have complete octets of electrons. • • • C O • ••
• • O • C • O •
• • •
• • •
• •
Shifting the unpaired electrons to form additional bonds (a double bond in this case) gives each atom a complete octet.
Double bonds involve two pairs, or four electrons • C O •• C O ••
Prentice-Hall © 2002
General Chemistry: Chapter 9

9. Multiple Covalent Bonds
Chemistry 140 Fall 2005
Multiple Covalent Bonds
We see for N2 that the formation of a triple bond is required to satisfy the octet of each nitrogen atom. • • N • •• •• N • • N •• • • N • •• N ••
Triple bonds involve three pairs, or six electrons
Multiple bond lengths are shorter than single bonds and release more energy when broken
Prentice-Hall © 2002
General Chemistry: Chapter 9

10. General Chemistry: Chapter 9
Chemistry 140 Fall 2005
11-3 Polar Covalent Bonds δ+ δ- H Cl
Nonpolar covalent bonds involve equa sharing of a pair of electrons.
This occurs when the two atoms involved have similar electronegativities
Polar covalent bonds involve the unequal sharing of a pair of electrons
The electrons spend more time around the atom with stronger electron attracting ability, higher electronegativity
This gives the more electronegative atom a partial negative charge and the lesser electronegative atom a partial positive charge.
Prentice-Hall © 2002
General Chemistry: Chapter 9

11. Electronegativity An atoms ability to compete for shared electrons.
Chemistry 140 Fall 2005
Electronegativity
An atoms ability to compete for shared electrons.
Related to ionization energy and electron affinity
Electronegativity follows the same trend as electron affinity and ionization energy.
Flourine has the highest electronegativity, Fancium has the least electronegativiy
The polarity of a bond is determined by the difference in electronegativity
Prentice-Hall © 2002
General Chemistry: Chapter 9

12. Percent Ionic Character
Chemistry 140 Fall 2005
Percent Ionic Character
The larger the difference in electronegativity between two bonded atoms, the higher the % ionic character of the bond.
The greater the difference in electronegativity, the more polar the bond.
Ionic bonds are the extreme polar bond, ΔEN greater than 1.7
Prentice-Hall © 2002
General Chemistry: Chapter 9

13. Writing Lewis Structures
Chemistry 140 Fall 2005
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.
Reintroduce Lewis structures
Prentice-Hall © 2002
General Chemistry: Chapter 9

14. General Chemistry: Chapter 9
Skeletal Structure
Identify central and terminal atoms. H H H C C O H H H
Many times this becomes apparent with the way that the molecular formula is written (CH3CH2OH) and using some intuition.
Prentice-Hall © 2002
General Chemistry: Chapter 9

15. Some general trends and rules
Chemistry 140 Fall 2005
Skeletal Structure
Some general trends and rules
Hydrogen atoms are always terminal atoms.
Central atoms are generally those with the lowest electronegativity.
Carbon atoms are always central atoms.
Generally structures are compact and symmetrical.
H can only accommodate two electrons
H and O are common exceptions to rule 2
Organic compounds are not compact nor symmetrical.
Prentice-Hall © 2002
General Chemistry: Chapter 9

16. Strategy for Writing Lewis Structures
Prentice-Hall © 2002
General Chemistry: Chapter 9