Ionic Compounds and MetalsIonic Compounds and Metals

CHAPTER 7 SOLUTIONS MANUAL Ionic Compounds and Metals

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Section 7.1 Ion Formation

pages 206?209

Section 7.1 Assessment

page 209

1. Compare the stability of a lithium atom with that of its ion, Li.

The Li+ ion is more stable because it has a complete octet.

2. Describe two different causes of the force of attraction in a chemical bond.

The two causes are the attraction between the positive nucleus of one atom and the negative electrons of another atom, and the attraction between positive ions and negative ions.

3. Apply Why are all of the elements from group 18 relatively unreactive, whereas those in group 17 are very reactive?

The group 18 elements, known as noble gases, have complete outer energy levels and do not easily form ions. The group 17 elements are highly reactive because they need only to gain a single electron to form an octet.

4. Summarize ionic bond formation by correctly pairing these terms: cation, anion, electron gain, electron loss.

{anion, electron gain}, {cation, electron loss}

5. Apply Write out the electron configuration for each atom. Then predict the change that must occur in each to achieve a noble gas configuration. a. nitrogen

[He]2s22p3; gain 3 electrons (3 ion) or lose 5 electrons (5 ion)

b. sulfur

[Ne]3s23p4; gain 2 electrons (2 ion)

c. barium

[Xe]6s2; lose 2 electrons (2 ion)

d. lithium

[He]2s1; lose 1 electron (1 ion)

6. Model Draw models to represent the formation of the positive calcium ion and the negative bromide ion.

Models should show that the calcium atom loses two electrons, forming Ca2, and that bromine gains one electron, forming Br. The models should also show the addition of energy to form the calcium ion, and the release of energy to form the bromide ion.

Section 7.2 Ionic Bonds and Ionic Compounds

pages 210?217

Practice Problems

page 212

Explain how an ionic compound forms from these elements.

7. sodium and nitrogen

Three Na atoms each lose 1 e, forming 1 ions.

One N atom gains 3 e, forming a 3 ion. The

ions attract, forming Na3N.

(_) (_) 3 Na ions 1 1 N ion 3

Na ion

N ion

3(1) 1(3) 0

The overall charge on one formula unit of Na3N is zero.

8. lithium and oxygen

Two Li atoms each lose 1 e, forming 1 ions.

One O atom gains 2 e, forming a 2 ion. The

ions attract, forming Li2O.

(_) (_) 2 Li ions 1 1 O ion 2

Li ion

O ion

2(1) 1(2) 0

The overall charge on one formula unit of Li2O is zero.

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9. strontium and fluorine

One Sr atom loses 2 e, forming a 2 ion. Two F

atoms each gain 1 e, forming 1 ions. The ions

attract, forming SrF2.

(_) (_) 1 Sr ion 2 2 F ions 1

Sr ion

F ion

1(2) 2(1) 0

The overall charge on one formula unit of SrF2 is zero.

10. aluminum and sulfur

Two Al atoms each lose 3 e, forming 3 ions.

Three S atoms gain 2 e each, forming 2 ions.

The ions attract, forming Al2S3.

(_) (_) 2 Al ions 3 3 S ions 2

Al ions

S ion

2(3) 3(2) 0

The overall charge on one formula unit of Al2S3 is zero.

11. Challenge Explain how elements in the two groups shown on the periodic table at the right combine to form an ionic compound.

Group 1

Group 15

Three group 1 atoms loses 1 e, forming 1 ions. One group 15 atom gains 3 e, forming a 3 ion. The ions attract, forming X3Y, where X represents a group 1 atom and Y represents a group 15 atom.

Section 7.2 Assessment

page 217

12. Explain how an ionic compound made up of charged particles can be electrically neutral.

The total positive charge of the cations in the compound equals the total negative charge of the anions in the compound.

13. Describe the energy change associated with ionic bond formation, and relate it to stability.

Ionic bond formation is exothermic; the lowerenergy product is more stable than the original reactants.

14. Identify three physical properties of ionic compounds that are associated with ionic bonds, and relate them to bond strength.

Ionic compounds exist as crystals, have high melting and boiling points, and are hard, rigid, and brittle. They are conductive when dissolved or molten but not when solid. All of these properties are due to the strength of the electrostatic attraction of oppositely-charged ions in close proximity.

15. Explain how ions form bonds and describe the structure of the resulting compound.

Electrons are transferred between atoms forming ions. Electrostatic forces hold the ions together in the ionic compound. The ions are arranged in a regular repeating pattern in an ionic crystal.

16. Relate lattice energy to ionic-bond strength.

As lattice energy becomes more negative, the stronger is the attraction between the ions and, thus, the stronger the ionic bond.

17. Apply Use electron configurations, orbital notation, and electron-dot structures to represent the formation of an ionic compound from the metal strontium and the nonmetal chlorine.

Drawing should include one Sr atom losing 2 e and forming an Sr2 ion, and two Cl atoms each gaining 1 e and forming two Cl ions. These ions attract, forming SrCl2.

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104 Chemistry: Matter and Change ? Chapter 7

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Electron Configuration

[Ne]3s23p5

[Kr]5s2 +

[Ne]3s23p5

[Ar] [Kr] +

[Ar]

Sr

2Cl

Sr2+ 2Cl-

Orbital Notation

1s 2s 2p 3s 3p 4s

3d

Sr

e-

+ 1s 2s

2p

3s

3p

4p 5s

1s 2s

2p

3s

3p

e-

2Cl

1s 2s 2p 3s 3p 4s

3d

Sr2+

Electron-dot Structures

e-

Sr +

e-

CCll

[Sr]2+

[ +

[

CCll

]- ]-

18. Design a concept map that shows the relationships among ionic bond strength, physical properties of ionic compounds, lattice energy, and stability.

Concepts maps will vary but should correlate greater bond strength to increased stability and a more negative lattice energy, and that physical properties such as high melting and boiling points, brittleness, and conductivity are due to the strength of ionic bonds.

Section 7.3 Names and Formulas for Ionic Compounds

pages 218?224

Practice Problems

pages 221?223

Write formulas for the ionic compounds formed by the following ions. 19. potassium and iodide

KI

20. magnesium and chloride

MgCl2

+ 1s 2s

2p

3s

3p

4p

1s 2s

2p

3s

3p

2Cl-

21. aluminum and bromide

AlBr3

22. cesium and nitride

Cs3N

23. Challenge Write the general formula for the ionic compound formed by elements from the two groups shown on the periodic table at the right.

Group 17 Group 2

The general formula is XY2, where X represents the group 2 element and Y represents the group 17 element.

Write formulas for ionic compounds composed of the following ions. 24. sodium and nitrate

NaNO3

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25. calcium and chlorate

Ca(ClO3)2

26. aluminum and carbonate

Al2(CO3)3

27. Challenge Write the formula for an ionic compound formed by ions from a group 2 element and polyatomic ions composed of only of carbon and oxygen.

The polyatomic ion is carbonate (CO32). The general formula is XCO3, where X is the symbol of a group 2 element.

Name the following compounds. 28. NaBr

sodium bromide

29. CaCl2

calcium chloride

30. KOH

potassium hydroxide

31. Cu(NO3)2

copper(II) nitrate

32. Ag2CrO4

silver chromate

33. Challenge The ionic compound NH4ClO4 is key reactant used in solid rocket boosters, such as those that power the space shuttle into orbit. Name this compound.

ammonium perchlorate

Section 7.3 Assessment

page 224

34. State the order in which the ions associated with a compound composed of potassium and bromine would be written in the chemical formula and the compound name.

The cation (potassium) is stated first, followed by the anion (bromide).

35. Describe the difference between a monatomic ion and a polyatomic ion and give an example of each.

Monatomic ions are one-atom ions (example, Cl); polyatomic ions are two or more atoms grouped together having a net charge (example, ClO3).

36. Apply Ion X has a charge of 2 and ion Y has a charge of 1. Write the formula unit of the compound formed from the ions.

XY2

37. State the name and formula for the compound formed from Mg and Cl.

magnesium chloride, MgCl2

38. Write the name and formula for the compound formed from sodium ions and nitrite ions.

sodium nitrite, NaNO2

39. Analyze What subscripts would you most likely use if the following substances formed an ionic compound? a. an alkali metal and a halogen

1, 1

b. an alkali metal and a nonmetal from group 16

2, 1

c. an alkaline earth metal and a halogen

1, 2

d. an alkaline earth metal and a nonmetal from group 16

1, 1

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106 Chemistry: Matter and Change ? Chapter 7

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Section 7.4 Metallic Bonds and the Properties of Metals

pages 225?228

Section 7.4 Assessment

pages 228

40. Contrast the structures of ionic compounds and metals.

Ions in ionic compounds are arranged in a repeating pattern of alternating charges, whereas metals consist of fixed cations surrounded by a sea of mobile, or delocalized, electrons.

41. Explain how the conductivity of electricity and the high melting points of metals are explained by metallic bonding.

Delocalized electrons can move through the solid to conduct an electric current. The number of delocalized electrons and the strength of a metallic bond determine the melting point.

42. Contrast the cause of the attraction in ionic bonds and metallic bonds.

Ionic bonds are held together by the electrostatic force of attraction between ions, whereas a metallic bond is due to the attraction of metallic cations for delocalized electrons.

43. Summarize alloy types by correctly pairing these terms and phrases: substitutional, interstitial, replaced, filled in.

{substitutional, replaced}, {interstitial, filled in}

44. Design an Experiment Describe an experiment that could be used to distinguish between a metallic solid and an ionic solid. Include at least two different methods for comparing the solids. Explain your reasoning.

A typical student experiment might have steps similar to the following:

1. Test each solid with a conductivity tester.

2. Place the solid in water to determine if it forms a solution.

3. Test the solution with a conductivity tester to determine if it conducts an electric current.

4. Use a hammer to strike the solid and record your observations.

Metallic solids conduct an electric current in the solid state, whereas ionic compounds do not. Metals may react with water, but they do not dissolve in water. Solutions containing ionic compounds conduct an electric current. Metallic solids are malleable and will deform when struck with a hammer, whereas ionic compounds are brittle and will break into pieces when struck with a hammer.

45. Model Draw a model to represent the physical property of metals known as ductility, or the ability to be drawn into a wire. Base your drawing on the electron sea model shown in Figure 7.11.

+ -

+

-

+ -

+ -

+

-

+ -

+-+

+

-

+-

-

-+

+ -

+

+

-

+ -

-+ --

+ -

-+ -

+-

+

Diagrams should show metal ions being moved into a longer, thinner form through a sea of electrons.

Everyday Chemistry

Writing in Chemistry

Sense of Danger Our sense of taste can detect certain toxins found naturatlly in plants. Researcg other modern toxins, such as lead and antifreeze, to find out why they don't eicit a negative response from our taste buds. For more on green chemistry, visit .

Student research should cite speculation by scientists that becsause humans and their ancestors did not often encounter elemental lead (or other modern toxins) in the natural environment, we have evolved having no natural aversion to eating the toxin. In fact, certain lead compounds found in paint (such as lead acetate) have a sweet taste. Research might also discuss how, contrary to the situation with lead, many plant-produced toxins have a bitter taste. This is likely due to the fact that humans and plants have co-evolved for millions of years.

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