1. Section 12.1 Characteristics of Chemical Bonds Steven S. Zumdahl Susan A. Zumdahl Donald J. DeCoste Gretchen M. Adams University of Illinois at Urbana-Champaign Chapter 12 Chemical Bonding

2. Section 12.1 Characteristics of Chemical Bonds 1.To learn about ionic and covalent bonds and explain how they are formed 2.To learn about the polar covalent bond 3.To understand the nature of bonds and their relationship to electronegativity 4.To understand bond polarity and how it is related to molecular polarity Objectives

3. Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds Bond – force that holds groups of atoms together and makes them function as a unit Bond energy – energy required to break a chemical bond

4. Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds Ionic compound results when a metal reacts with a nonmetal. Ionic Bonding

5. Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds A covalent bond results when electrons are shared by nuclei. Covalent Bonding

6. Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds A polar covalent bond results when electrons are shared unequally by nuclei. Covalent Bonding  One atom attracts the electrons more than the other atom.

7. Section 12.1 Characteristics of Chemical Bonds B. Electronegativity Electronegativity – the relative ability of an atom in a molecule to attract shared electrons to itself  Increases from left to right across a period  Decreases down a group of representative elements

8. Section 12.1 Characteristics of Chemical Bonds Concept Check If lithium and fluorine react, which has more attraction for an electron? Why? In a bond between fluorine and iodine, which has more attraction for an electron? Why?

9. Section 12.1 Characteristics of Chemical Bonds Concept Check What is the general trend for electronegativity across rows and down columns on the periodic table? Explain the trend.

10. Section 12.1 Characteristics of Chemical Bonds B. Electronegativity The polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bond.

11. Section 12.1 Characteristics of Chemical Bonds B. Electronegativity

12. Section 12.1 Characteristics of Chemical Bonds Exercise Arrange the following bonds from most to least polar: a) N–FO–FC–F b)C–FN–OSi–F c)Cl–ClB–ClS–Cl a) C–F, N–F, O–F b) Si–F, C–F, N–O c) B–Cl, S–Cl, Cl–Cl

13. Section 12.1 Characteristics of Chemical Bonds Concept Check Which of the following bonds would be the least polar yet still be considered polar covalent? Mg–O C–O O–O Si–O N–O

14. Section 12.1 Characteristics of Chemical Bonds Concept Check Which of the following bonds would be the most polar without being considered ionic? Mg–O C–O O–O Si–O N–O

15. Section 12.1 Characteristics of Chemical Bonds C. Bond Polarity and Dipole Moments A dipole moment results when a polar molecule has a center for positive charge separate from a center for negative charge.

16. Section 12.1 Characteristics of Chemical Bonds C. Bond Polarity and Dipole Moments Water molecule dipole moment

17. Section 12.1 Characteristics of Chemical Bonds C. Bond Polarity and Dipole Moments The polarity of water affects its properties.  Causes water to remain liquid at higher temperature  Permits ionic compounds to dissolve in it

18. Section 12.2 Characteristics of Ions and Ionic Compounds 1.To learn about stable electron configurations 2.To learn to predict the formulas of ionic compounds 3.To learn about the structures of ionic compounds 4.To understand factors governing ionic size Objectives

19. Section 12.2 Characteristics of Ions and Ionic Compounds A. Stable Electron Configurations and Charges on Ions

20. Section 12.2 Characteristics of Ions and Ionic Compounds A. Stable Electron Configurations and Charges on Ions

21. Section 12.2 Characteristics of Ions and Ionic Compounds A. Stable Electron Configurations and Charges on Ions Atoms in stable compounds usually have a noble gas electron configuration.  Metals lose electrons to reach noble gas configuration.  Nonmetals gain electrons to reach noble gas configuration.

22. Section 12.2 Characteristics of Ions and Ionic Compounds A. Stable Electron Configurations and Charges on Ions Chemical compounds are always electrically neutral. Predicting Formulas of Ionic compounds

23. Section 12.2 Characteristics of Ions and Ionic Compounds B. Ionic Bonding and Structures of Ionic Compounds Ions are packed together to maximize the attractions between ions. Structures of Ionic Compounds

24. Section 12.2 Characteristics of Ions and Ionic Compounds B. Ionic bonding and Structures of Ionic Compounds Cations are always smaller than the parent atom. Structures of Ionic Compounds Anions are always larger than the parent atom.

25. Section 12.2 Characteristics of Ions and Ionic Compounds B. Ionic bonding and Structures of Ionic Compounds Polyatomic ions work in the same way as simple ions.  The covalent bonds hold the polyatomic ion together so it behaves as a unit. Ionic Compounds Containing Polyatomic Ions

26. Section 12.3 Lewis Structures 1.To learn to write Lewis structures 2.To learn to write Lewis structures for molecules with multiple bonds Objectives

27. Section 12.3 Lewis Structures A. Writing Lewis Structures In writing Lewis structures, we include only the valence electrons. Most important requirement  Atoms achieve noble gas electron configuration (octet rule, duet rule).

28. Section 12.3 Lewis Structures A. Writing Lewis Structures Bonding pairs are shared between 2 atoms. Unshared pairs (lone pairs) are not shared and not involved in bonding.

29. Section 12.3 Lewis Structures A. Writing Lewis Structures

30. Section 12.3 Lewis Structures B. Lewis Structures of Molecules with Multiple Bonds Single bond – covalent bond in which 1 pair of electrons is shared by 2 atoms Double bond – covalent bond in which 2 pairs of electrons are shared by 2 atoms Triple bond – covalent bond in which 3 pairs of electrons are shared by 2 atoms

31. Section 12.3 Lewis Structures B. Lewis Structures of Molecules with Multiple Bonds

32. Section 12.3 Lewis Structures B. Lewis Structures of Molecules with Multiple Bonds  Boron – incomplete octet Some Exceptions to the Octet Rule  Molecules containing odd numbers of electrons – NO and NO 2

33. Section 12.3 Lewis Structures Concept Check Draw a Lewis structure for each of the following molecules: H2H2 F2F2 HF

34. Section 12.3 Lewis Structures Concept Check Draw a Lewis structure for each of the following molecules: NH 3 CO 2 CCl 4