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Free Study Guide forCracolice • Peters

Introductory Chemistry: An Active Learning ApproachSecond Edition

www.brookscole.com/chemistry

Chapter 11Chemical Bonding

Chapter 11–Assignment A: Ionic and Covalent Bonding

A chemical bond may be defined as a force that holds atoms together to form molecules orions (in this assignment) or metals (in Assignment B). The term chemical bond also refersto the force that holds oppositely charged ions together to form ionic compounds. In allcases, chemical bonds are formed in a system if the total energy of that system decreasesafter the bond is formed. There is a natural tendency towards minimization of energy.

Ionic bonds between atoms appear to form when atoms of a metal lose one, two, or threeelectrons to form a cation that is isoelectronic with a noble gas and atoms of a nonmetal gainone, two, or three electrons to form an anion that is also isoelectronic with a noble gas.Bonds also form between two nonmetals, both of which have atoms that are one, two, oreven three electrons short of a noble gas electron configuration. This is accomplishedthrough covalent bonding, in which electrons are shared. Look for these big ideas:

1) Many monatomic ions are isoelectronic with noble gas atoms, which have an octet(8) of valence electrons. The “complete octet” is a convenient memory aid.

2) An ionic bond, also called an electron-transfer bond, is formed because of theelectrostatic attraction between oppositely charged ions.

3) Covalent bonds form when two atoms achieve a noble gas octet by sharing one ormore pairs of electrons.

Learning Procedures

Study Sections 11.1–11.3. Focus on Goals 1–6 as you study.

Strategy As you study ionic and covalent bonds, compare and contrast these bonding types. We suggest that you set up a table, listing ionic bonding in one column and covalent bonding in another. Items for comparison should include: the periodic table and its relationship to ionic vs. covalent bonds, how atoms achieve noble gas configurations in each bonding type, and how the phrases electron transfer and electron sharing correlate with the bonding types.

Answer Questions, Exercises, and Problems 1–9. Check your answers with those at the end of the chapter.

Chapter 11 Chemical Bonding

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Workbook If your instructor recommends the Active Learning Workbook, doQuestions, Exercises, and Problems 1–9.

Chapter 11–Assignment B: More About Covalent Bonding; Metallic Bonds

In Assignment A you learned that covalent bonds are characterized by sharing of electrons.Are the bonding electrons shared equally? If the bonding electrons are not shared equally,can we predict which of the two atoms gets the bigger share?

We also see in this assignment that covalent bonding applies to many-atom molecules, andthat the bonds between atoms can involve more than one pair of electrons.

Finally, you will learn about bonding among metal atoms. These are appropriately calledmetallic bonds and can be thought of as positively charged metal cations floating in a sea ofnegatively charged electrons.

Watch for these key ideas:

1) In a nonpolar covalent bond, the bonding electrons are shared equally by the bondedatoms. In a polar covalent bond, one atom attracts the shared electrons morestrongly than the other.

2) The relative ability of atoms of an element to attract electron pairs in covalent bondsis expressed by the electronegativity of the element.

3) The polarity of a bond is estimated by the difference in electronegativities of thebonded atoms. The atom with the higher electronegativity is the negative end of thebond. The atom with the lower electronegativity is the positive end of the bond.

4) Metallic bonding occurs because of attractive forces between negatively chargedvalence electrons moving among positively charged metal ions.

Learning Procedures

Study Sections 11.4–11.8. Focus on Goals 7–12 as you study.

Strategy This is conceptual material. Study the text carefully, focusing on thevocabulary and its applications.

Answer Questions, Exercises, and Problems 10–20. Check your answers with thoseat the end of the chapter.

Workbook If your instructor recommends the Active Learning Workbook, doQuestions, Exercises, and Problems 10–20.

Study Guide for Introductory Chemistry: An Active Learning Approach

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Chapter 11–Assignment C: Summary and Review

Three models describe the chemical “glue” that holds compounds together. In thisintroductory course, we present these models as absolutes: a bond is either ionic (electron-donating) or covalent (electron-sharing) or metallic (electron-sea). In more advancedcourses, you will see that these three models are extremes, used to help you learn how atomsbond. As in most cases involving extreme positions, the truth is found somewhere in themiddle.

Learn well the trends in electronegativity. It increases from left to right across a period andalso increases from bottom to top in a group. If you remember that F is the mostelectronegative element, you can easily remember those trends. Electronegativity is the keyto determining electrostatic attractions in bonds and compounds. In your later chemistrycourses, you will see that electronegativity is the link between many different concepts, andit makes them all fit together. Don't underestimate its value.

In this chapter and also in Chapter 12 you use the idea of a noble gas electron configuration,or complete octet. There is no magic in a complete octet; Section 11.8, Exceptions to theOctet Rule, is proof that the octet rule is fallible. An ionic bond forms because ofelectrostatic attractions of the ions, not because of the noble gas electron configurationsthose ions happen to have. Use the octet rule for what it is, a memory aid, and no more.

Learning Procedures

Review your lecture and textbook notes.

the Chapter in Review and the Key Terms and Concepts, and read the StudyHints and Pitfalls to Avoid.

Answer Concept-Linking Exercises 1–6. Check your answers with those at the endof the chapter.

Questions, Exercises, and Problems 21–27. Include Questions 28–32 ifassigned by your instructor. Check your answers with those at the end of thechapter.

Workbook If your instructor recommends the Active Learning Workbook, doQuestions, Exercises, and Problems 21–24. Include Questions 25–29 ifassigned by your instructor.

Take the chapter summary test that follows. Check your answers with those at theend of this assignment.

Chapter 11 Sample Test

Instructions: You may use a “clean” periodic table.

1) Which of the following is not an anion?a) F— b) NO3

– c) HPO42 – d) K+ e) N3 –

2) Which of the following is not isoelectronic with a noble gas?a) Na+ b) Cl– c) S2 – d) Al3+ e) Zn2+

Chapter 11 Chemical Bonding

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3) A bond formed by the transfer of an electron from one atom to another is called a(n)_____ bond.a) ionic b) covalent c) metallic d) nonpolar e) Lewis

4) Identify the incorrect statement among the following.a) The bond between hydrogen atoms in H—H is a covalent bond.b) When two bonding electrons are shared by two atoms, they count as valence

electrons for only the least electronegative atom.c) The Cl2 bond is formed by the overlap of half-filled 3p orbitals of two chlorine

atoms.d) The stability of a noble-gas electron configuration contributes to the formation

of a covalent bond.e) When a covalent bond forms, the charge density is concentrated in the region

between the two nuclei.

5) How many bonding electron pairs (_____) and how many lone pairs (_____) are ina nitrogen molecule? : N ≡ N :

6) Identify each of the following bonds as either primarily ionic or primarily covalent:a) Na—F b) Ba—Br c) C—H d) N—O

7) Identify the incorrect statement among the following:a) The bond between two atoms of the same element is probably less polar than the

bond between two atoms of different elements.b) The distribution of electronic charge in a polar bond is not symmetrical.c) A bonding electron pair does not tend to be closer to either of the bonded atoms

if the bond is polar.d) One end of a polar bond is said to be the negative pole.e) You can estimate the polarity of a bond by calculating the difference between the

electronegativity values for the bonded elements.

8) Which of the following best describes the C—O bond?a) Nonpolarb) Polar covalent with C as the + end of the bondc) Polar covalent with O as the + end of the bondd) Ionice) Metallic

9) Rank the following bonds in order of decreasing polarity:C—C C—H C—N C—O

10) Identify the incorrect statement among the following.a) An alloy is a solid mixture of two or more elements that has macroscopic

metallic properties.b) The fact that metals are good electrical conductors can be explained theoretically

by the nature of the metallic bond.c) The electrons in a metallic bond are localized.d) A metal effectively consists of metal ions surrounded by an electron sea.e) Metals are found to the left of the stair-step line in the periodic table.

Study Guide for Introductory Chemistry: An Active Learning Approach

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Answers to Chapter 11 Sample Test

1) d 2) e 3) a 4) b 5) 3 bonding electron pairs and 2 lone pairs6) a and b are primarily ionic; c and d are primarily covalent7) c 8) b 9) C—O > C—N > C—H > C—C 10) c