Ionic Bonds and Ionic Compounds

Transcription

1 7 Study Guide BIGIDEA BONDING AND INTERACTIONS Atoms form positive ions (cations) by losing valence electrons and form negative ions (anions) by gaining valence electrons. The electrostatic forces between the oppositely charged ions hold the cations and anions together in an ionic compound. Ionic compounds generally have high melting points and can conduct an electric current in solution and in the molten state. Metals are made up of closely packed cations surrounded by a sea of electrons. The sea-of-electrons model explains why metals are good conductors of electric current and why they are ductile and malleable. 7.1 Ions To find the number of valence electrons in an atom of a representative element, simply look at its group number. A positively charged ion, or a cation, is produced when an atom loses one or more valence electrons. An anion is produced when an atom gains one or more valence electrons. valence electron (194) electron dot structure (195) octet rule (195) halide ion (199) 7.2 Ionic Bonds and Ionic Compounds Although they are composed of ions, ionic compounds are electrically neutral. Most ionic compounds are crystalline solids at room temperature. Ionic compounds generally have high melting points. Ionic compounds can conduct an electric current when melted or dissolved in water. ionic compound (201) ionic bond (201) chemical formula (202) formula unit (202) coordination number (205) 7.3 Bonding in Metals The valence electrons of atoms in a pure metal can be modeled as a sea of electrons. Alloys are important because their properties are often superior to those of their component elements. metallic bond (209) alloy (211) Evaluate Review and Assessment Materials E ONLINE O P R O B L E M S R O M VIRTUAL L A B PROBLEM SETS Have students practice more formula writing problems by using the Chapter 7 Online Problem Set. VIRTUAL LABS Have students complete a virtual lab as an in-class or take-home assignment to help reinforce the concept of ionic bonding. Study Tip Write and answer questions about the content of the chapter. For Chapter 7, you might ask the following questions, which require students to summarize the information contained in the chapter. What information does the electron dot structure of an element provide? (the number of valence electrons) In most cases, what is the stable electron configuration of an elemental ion? (In most cases, a stable configuration is characterized by an octet of valence electrons; the configuration is isoelectronic with that of a noble gas.) Why does NaCl dissolved in water conduct electricity? (In water, the ionic compound breaks apart into Na + and Cl ions that are free to move in the solution.) What is the theory of bonding in pure metals? (metal cations held together by a pool of mobile valence electrons) STUDY GUIDE Study Guide 213 Performance Tasks MODELING IONIC CRYSTALS Have students choose three ionic compounds and do research to find out their crystal structures. Then have students use modeling clay and toothpicks to make three-dimensional models of each crystal structure. QUENCHING NOT JUST FOR THIRST Alloys and metals are often quenched in water after being heated and shaped. Have students research and report on the effects of quenching on the crystalline structure of metals and alloys. Also, ask them to compare the resulting crystals to ionic crystals. Reports should include any necessary graphics and explain any changes in metal properties that occur as a result of the quenching process. Study Guide 213

2 ASSESSMENT LESSON an electron in the highest occupied energy level 28. a. Group 5A; 5 valence electrons b. Group 1A; 1 valence electron c. Group 5A; 5 valence electrons d. Group 2A; 2 valence electrons e. Group 7A; 7 valence electrons f. Group 4A; 4 valence electrons 29. a. Cl b. S c. Al d. Li 30. by gaining or losing electrons 31. a. 2 b. 3 c. 1 d a. Al 3+ b. Li + c. Ba 2+ d. K + e. Ca 2+ c. Sr Most nonmetals gain 1, 2, or 3 electrons to achieve a noble-gas electron configuration. 34. a. 3 b. 2 c. 1 d a. S 2 b. Na + c. F d. P a. gain of 1 electron b. loss of 1 electron c. gain of 3 electrons d. loss of 2 electrons e. loss of 2 electrons f. loss of 1 electron g. gain of 1 electron h. loss of 2 electrons 37. a. bromide anion b. sodium cation c. arsenide anion d. barium cation e. calcium cation f. copper(i) cation g. hydride anion h. copper(ii) cation LESSON the electrostatic force that holds ions together in ionic compounds 39. The positive charges balance the negative charges. 40. a, c, e 41. a, b, d 42. with the formula that reflects the ratio of ions in the compound 43. a. Ca 2+, F b. Al 3+, Br c. Li +, O 2 d. Al 3+, S 2 e. K +, N a. K +, Cl b. Ba 2+, S 2 c. Mg 2+, Br d. Li +, O Their network of electrostatic attractions and repulsions forms a rigid structure. 46. Ions are free to move in molten MgCl 2. O ONLINE P R O B L E M S R O E M 7 Assessment Lesson by Lesson 7.1 Ions 27. What is a valence electron? 28. To which group in the periodic table does each of the following elements belong? How many valence electrons do atoms of each element have? a. nitrogen d. barium b. lithium e. bromine c. phosphorus f. carbon 29. Write electron dot structures for each of the following elements: a. Cl c. Al b. S d. Li 30. Describe two ways that an ion forms from an atom. 31. How many electrons must an atom of each element lose to attain a noble-gas electron configuration? a. Ca c. Li b. Al d. Ba 32. Write the symbol for the ion formed when each of the following elements loses its valence electrons. a. aluminum d. potassium b. lithium e. calcium c. barium f. strontium 33. Why do nonmetal atoms tend to form anions when they react to form compounds? 34. How many electrons must be gained by each of the following atoms to achieve a stable electron configuration? a. N c. Cl b. S d. P 35. What is the formula of the ions formed when atoms of the following elements gain or lose valence electrons and attain noble-gas configurations? a. sulfur c. fluorine b. sodium d. phosphorus 214 Focus on ELL 36. State the number of electrons either lost or gained in forming each ion. a. Br e. Ca 2 b. Na f. Cu 3 c. As g. H 2 d. Ba h. Cu Name each ion in Problem 36. Identify each as an anion or a cation. 7.2 Ionic Bonds and Ionic Compounds 38. Define an ionic bond. 39. Explain why ionic compounds are electrically neutral. 40. Which of the following pairs of atoms would you expect to combine chemically to form an ionic compound? a. Li and S d. F and Cl b. O and S e. I and K c. Al and O f. H and N 41. Which of the following pairs of elements will not form ionic compounds? a. sulfur and oxygen b. sodium and calcium c. sodium and sulfur d. oxygen and chlorine 42. How can you represent the composition of an ionic compound? 43. Identify the kinds of ions that form each ionic compound. a. calcium fluoride, CaF2 b. aluminum bromide, AlBr3 c. lithium oxide, Li2O d. aluminum sulfide, Al2S 3 e. potassium nitride, K3N 44. Write the formulas for the ions in the following compounds: a. KCl c. MgBr 2 b. BaS d. Li 2 O 45. Most ionic substances are brittle. Why? 46. Explain why molten MgCl2 does conduct an electric current although crystalline MgCl 2 does not. 5 ASSESS UNDERSTANDING Engage students in discussing the chapter s key concepts and vocabulary. Encourage them to identify learning strategies they felt were most helpful and those they felt were difficult. BEGINNING: LOW/HIGH Provide students with a two-column chart which has randomly ordered vocabulary words in one column and definitions in the other. Have students match each word with its definition. INTERMEDIATE: LOW/HIGH Provide students with a list of one key question from each lesson. Have them write a short answer to each. ADVANCED: LOW/HIGH Have students write a summary statement for each lesson describing what they have learned. 214 Chapter 7 Assessment

3 7.3 Bonding in Metals 47. How can you describe the arrangement of atoms in metals? 48. Explain briefly why metals are good conductors of electric current. 49. Name the three crystal arrangements of closely packed metal atoms. Give an example of a metal that crystallizes in each arrangement. 50. Name some alloys that you have used or seen today. 51. Explain why the properties of all steels are not identical. Understand Concepts 52. Construct a table that shows the relationship among the group number, valence electrons lost or gained, and the formula of the cation or anion produced for the following metallic and nonmetallic elements: Na, Ca, Al, N, S, Br. 53. Write electron dot structures for the following elements. a. C d. F b. Be e. Na c. O f. P 54. Show the relationship between the electron dot structure of an element and the location of the element in the periodic table. 55. In terms of electrons, why does a cation have a positive charge? 56. Why does an anion have a negative charge? 57. The spheres below represent the relative diameters of atoms or ions. Rearrange the sequences in (a) and (b) so the relative sizes of the particles correspond to the increasing size of the particles as shown in the illustration. a. oxygen atom, oxide ion, sulfur atom, sulfide ion b. sodium atom, sodium ion, potassium atom, potassium ion 64. fluorine, chlorine, bromine, and iodine; Group 7A, 7 valence electrons 65. a. 1s 2 2s 2 2p 6 3s 2 3p 6 b. 1s 2 2s 2 2p 6 ; Each has a noble-gas electron configuration 58. Write the name and symbol of the ion formed when a. a sulfur atom gains two electrons. b. an aluminum atom loses three electrons. c. a nitrogen atom gains three electrons. d. a calcium atom loses two electrons. 59. Write electron configurations for the 2 cations of these elements. a. Fe b. Co c. Ni 60. Write electron configurations for the 3 cations of these elements. a. chromium b. manganese c. iron 61. Write the symbol for the ion formed when each element gains electrons and attains a noble-gas electron configuration. a. Br c. As b. H d. Se 62. Write electron configurations for the following atoms and ions, and comment on the result. a. Ar c. S 2 b. Cl d. P Write electron configurations for the following atoms and ions and comment on the result. 3 a. N c. F 2 b. O d. Ne 64. Name the first four halogens. What group are they in, and how many valence electrons does an atom of each element have? 65. Write complete electron configurations for the following atoms and ions. For each group, comment on the results. a. Ar, K, Ca 2 b. Ne, Na, Mg 2, Al If ionic compounds are composed of charged particles (ions), why isn t every ionic compound either positively or negatively charged? 67. Which of the following compounds are most likely not ionic? a. H2O d. CaS b. Na2O e. SO 2 c. CO2 f. NH 3 Ionic and Metallic Bonding The positively charged cations exactly balance the negatively charged anions. 67. a, c, e, f LESSON Sample answer: Atoms in metals are arranged in a compact and orderly manner. 48. They have many mobile valence electrons. Electrons in the current replace the electrons leaving the metal. 49. body-centered cubic: Na, K, Fe, Cr, or W; face-centered cubic: Cu, Ag, Au, Al, or Pb; hexagonal close-packed: Mg, Zn, or Cd 50. could include table-ware, steel in cars and buses, high-speed dental drill bits, solder in stereos and televisions, and structural steel in buildings. 51. The properties of the steel will vary according to its composition. In addition to iron, steel can contain varying amounts of carbon and such metals as chromium, nickel, and molybdenum. UNDERSTAND CONCEPTS 52. Valence Group number electrons lost or gained Formula of ion 1A 1 Na + 2A 2 Ca 2+ 3A 3 Al 3+ 5A 3 N 3 6A 2 S 2 7A 1 Br 53. a. C c. O e. Na b. Be d. F f. P 54. For the representative elements the number of electrons in the electron dot structure is the group number. 55. It has lost valence electrons. 56. It has gained valence electrons. 57. a. oxygen atom, sulfur atom, oxide ion, sulfide ion b. sodium ion, potassium ion, sodium atom, potassium atom 58. a. sulfide ion (anion), S 2 b. aluminum ion (cation), Al 3+ c. nitride ion (anion), N 3 d. calcium ion (cation), Ca a. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 b. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 7 c. 1s 2 2s 2 2p 6 3s 2 3p 6 3d a. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 3 b. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 4 c. 1s 2 2s 2 2p 6 3s 2 3p 6 3d a. Br b. H c. As 3 d. Se All have the noble-gas configuration of 1s 2 2s 2 2p 6 3s 2 3p All are 1s 2 2s 2 2p 6. All have the same configuration as neon. ASSESSMENT Ionic and Metallic Bonding 215

4 ASSESSMENT UNDERSTAND CONCEPTS 68. a. BaBr 2 b. Al 2 S 3 c. K 3 N 69. Their outmost occupied energy levels are filled. 70. a. Fe 2 O 3 b. PbO 2 c. Li 2 O d. MgO 71. No, the packing of ions in a crystalline structure depends on a number of factors including the relative sizes of the ions. The coordination number of an element can vary from compound to compound Hexagonal close-packed unit cells have twelve neighbors for, every atom or ion. Face-centered cubic unit cells also have twelve neighbors for every atom or ion, with an atom or ion in the center of each face. Body-centered cubic unit cells have eight neighbors for every atom or ion, with an atom or ion at the center of each cube. 74. Brass is a mixture of copper and zinc. The properties of a particular sample of brass will vary with the relative proportions of the two metals. 75. a. Cu, Zn c. Cu, Sn b. Ag, Cu d. Fe, Cr, Ni, C THINK CRITICALLY 76. Each dot in the electron dot structure represents a valence electron in the electron configuration diagram. 77. By gaining or losing electrons the atoms of elements achieve a noble-gas electron configuration. 78. No, sodium chloride is composed of equal numbers of sodium ions and chloride ions; the ions are in a 1:1 ratio. Each sodium ion is surrounded by chloride ions, and each chloride is surrounded by sodium ions. 79. a. 6A d. 6A b. 7A e. 1A c. 1A f. 2A 80. In sodum chloride crystals the sodium and chloride ions vibrate about fixed points; in the molten state, the ions are free to move. 81. Metals are ductile (can be drawn into wires) and malleable (can be hammered into shapes). These changes are possible because a metal consists of metal cations in a sea of valence electrons. When subjected to pressure, the cations easily slide past one another. 82. The spheres are more closely packed in (a); there is less empty space in (a), and a rough count shows 25 spheres in (a) compared with 22 spheres in (b). 68. Write the formulas for each ionic compound that can be made by combining each of pair of ions. 2 a. Ba and Br 3 b. Al and S 2 c. K and N The atoms of the noble gas elements are stable. Explain. 70. What is the simplest formula for the compounds that can form when each of these ions combine with an oxide (O 2 ) ion? 3 a. Fe c. Li 4 b. Pb d. Mg Can you predict the coordination number of an ion from the formula of an ionic compound? Explain. 72. Metallic cobalt crystallizes in a hexagonal close-packed structure. How many neighbors will a cobalt atom have? 73. Explain how hexagonal close-packed, facecentered cubic, and body-centered cubic unit cells are different from one another. Body-centered cubic 74. The properties of all samples of brass are not identical. Explain. 75. For each alloy below, list the elements it contains. a. brass c. bronze b. sterling silver d. stainless steel Think Critically Face-centered cubic 76. Make Generalizations What is the relationship between the number of electrons in the valence shells in an electron configuration diagram for an atom and the number of dots in the corresponding electron dot structure? 77. Relate Cause and Effect Why are many elements more stable as ions than they are as atoms? 216 Hexagonal close-packed 83. Both metals and ionic compounds are composed of ions. Both are held together by electrostatic bonds. Metals always conduct electricity, and ionic compounds conduct only when melted or in water solution. Ionic compounds are composed of cations and anions, but metals are composed of cations and freefloating valence electrons. Metals are ductile, but ionic compounds are brittle. 78. Make Generalizations Is it accurate to describe sodium chloride (NaCl) as consisting of individual particles, each made up of one Na cation and one Cl anion? Explain your answer. 79. Infer For each ionic formula, identify the A-group number to which element X belongs. a. CaX d. Al 2 X 3 b. MgX2 e. XF c. X3N f. XS 80. Compare How do the motions of sodium ions and chloride ions in molten sodium chloride differ from the motions of these ions in sodium chloride crystals? 81. Relate Cause and Effect Two physical properties of metals are ductility and malleability. Explain these properties based on what you know about the valence electrons of metal atoms. 82. Interpret Diagrams How atoms and ions are arranged in crystals is not just dependent on size. The spheres in each atomic window below are identical in size. The windows have exactly the same area. In which window are the spheres more closely packed? Explain your reasoning. a. b. 83. Compare and Contrast Describe the similarities and differences between ionic compounds and metals in terms of their physical and chemical characteristics. 84. Relate Cause and Effect How does the octet rule explain the large increase in energy between the first and second ionization energies of Group 1A metals? 85. Infer An atom of the element M forms a stable ion in an ionic compound with chlorine having the formula MCl 2. In this compound, the ion of element M has a mass number of 66 and has 28 electrons. a. What is the identity of the element? b. How many neutrons does the ion have? 84. Removal of the first electron results in a very stable electron configuration. Removing a second electron would disrupt that stability. 85. a. zinc b. 38 neutrons 216 Chapter 7 Assessment

5 Enrichment 86. Apply Concepts Classify each element in the following list. Will an atom of each element form a cation or an anion, or is the element chemically nonreactive? For the atoms that do form ions during a chemical reaction, write the number of electrons the atom will gain or lose. a. lithium b. sodium c. neon d. chlorine e. magnesium 87. Infer The chemically similar alkali metal chlorides NaCl and CsCl have different crystal structures, whereas the chemically different NaCl and MnS have the same crystal structures. Why? Cl Na Sodium chloride (NaCl) Cl Cs Cesium chloride (CsCl) 88. Calculate Silver crystallizes in a face-centered cubic arrangement. A silver atom is at the edge of each lattice point (the corner of the unit cell). The length of the edge of the unit cell is nm. What is the atomic radius of silver? 89. Analyze Data Consider two ionic compounds, NaCl and CaO. a. In which compound would you expect the electrostatic forces that hold the compound together to be the strongest? Explain your choice. b. The melting point of NaCl is 801 C. The melting point of CaO is 2614 C. Does this data support your prediction? Why or why not? Write About Science 90. Compare Describe the formation of a cation that is an exception to the octet rule. In your description, compare the electron configuration of the cation to the electron configurations of the nearest noble gases. 91. Research Go online and research X-ray diffraction crystallography. How are the samples prepared? How are the X-rays generated and detected? How is this technique used to study the structure of crystalline substances? CHEMYSTERY It s Not Easy Being Green The statue of Ludwig van Beethoven in Central Park is made of bronze. Bronze is an alloy containing copper and tin. When bronze is exposed to the elements, it reacts with water (H 2 O), carbon dioxide (CO 2 ), and oxygen (O 2 ) in the air to produce a film of copper(ii) carbonate (CuCO 3 ). Copper(II) carbonate is an ionic compound that is blue-green in color. A film of copper(ii) carbonate on the Beethoven statue gives the statue its green color. The film also protects the metal against further corrosion. 92. Apply Concepts A copper atom can lose one or two electrons to form a Cu ion or a Cu 2 ion, respectively. The charge of the copper ion in CuCO 3 is 2. Write the electron configuration of this cation. 93. Form an Opinion Why do you think bronze is often used to create statues? 94. Connect to the BIGIDEA How are the properties of the copper(ii) carbonate film on the statue different from the properties of the bronze beneath the film? Explain how these properties are a result of the type of bonding present. APPLY CONCEPTS After CHEMYSTERY students have read through the CHEMystery, discuss the principles of ionic and metallic bonding that make the development of the green patina possible. Ask What type of bonding occurs? (The product is an ionic compound composed of copper from the statue and water and carbon dioxide from the air.) Ask How is the film able to protect the metal against further corrosion? (Because the film has a different composition, it doesn t react with air in the same way that the metal does.) CHEMYSTERY ANSWERS 92. The configuration is [Ar]3d Sample answer: Bronze is an attractive metal alloy before and after it forms a patina. 94. The metallically-bonded alloy is able to react with elements in its environment to form an ionic compound, which is less reactive. ASSESSMENT Ionic and Metallic Bonding a. cation: lose 1e b. cation: lose 1e c. unreactive d. anion: gain 1e e. cation: lose 2e 87. Na + and Cs + differ greatly in size. Na + and Cl are similar in size to Mn 2+ and s nm 89. a. CaO; the electrostatic forces of attraction between Ca 2+ and O 2 are much stronger than the forces between Na + and Cl. b. Yes; more energy is needed to overcome the electrostatic attractions in CaO and melt the compound. WRITE ABOUT SCIENCE 90. An atom of silver has the electron configuration ls 2 2s 2 2p 6 3s 2 3p 6 3d l0 4s 2 4p 6 4d l0 5s 1. To achieve the configuration of the preceding noble gas, krypton, a silver atom would have to lose eleven electrons and form Ag 11+. To achieve the configuration of the following noble gas xenon, a silver atom must gain seven electrons and form Ag 7. Because ions with such high charges are unlikely, silver does not achieve a noble-gas configuration. However, if a silver atom loses its 5s 1 electron, the result is an outer electron configuration of eighteen electrons, written as 4s 2 4p 6 4d 10. This configuration is favored and stable. It is known as a pseudo-noble-gas configuration. 91. Remind students to use reliable sources and to document their sources. For such an extensive project, it might make sense for students to work in groups and divide up the tasks. Ionic and Metallic Bonding 217

6 ASSESSMENT CUMULATIVE REVIEW 95. Organic chemistry is the study of chemicals containing carbon; inorganic chemistry is the study of chemicals that do not contain carbon. 96. an analytical chemist 97. Conserve energy and develop renewable resources. 98. a, b, and d are chemical changes; c is a physical change 99. b and e; c is not a mixture, it is a pure substance 100. a. liquid, vapor b. vapor c. liquid, vapor d. liquid, vapor 101. a g b m c L d mg 102. b C cm a. 64 Zn c. 3 H 30 1 b Cl d Ca amu 107. Each of the isotopes has 8 protons and 8 electrons; oxygen-16 also has 8 neutrons, oxygen-17 has 9 neutrons, and oxygen-18 has 10 neutrons a. 1 b. 3 c. 1 d a. N, 1s 2 2s 2 2p 3 b. Be, 1s 2 2s 2 c. P, 1s 2 2s 2 2p 6 3s 2 3p 2 d. K, ls 2 2s 2 2p 6 3s 2 3p 6 4s chlorine, Cl, ls 2 2s 2 2p 6 3s 2 3p a m b. the visible region, green 112. a. K, 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 b. AI, ls 2 2s 2 2p 6 3s 2 3p 1 c. S, ls 2 2s 2 2p 6 3s 2 3p 4 d. Ba, ls 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 2 4d 10 5s 2 5p 6 6s the electron 114. sodium (Na), cesium (Cs), rubidium (Rb), lithium (Li) Cumulative Review 95. How is organic chemistry distinguished from inorganic chemistry? 96. What is the name given to a chemist who studies the composition of matter? 97. Explain two ways to meet modern society s need for energy. 98. Classify the following actions as chemical or physical changes. a. Cookies are baked. b. A firefly emits light. c. A figure is carved from wood. d. Caramel is made from sugar. 99. Which of the following substances is not a homogeneous mixture? a. gold ring b. spaghetti sauce c. cane sugar d. window glass e. river water f. bottled water 100. What physical state(s) can each of the following substances become as you raise its temperature? a. silver c. ice b. gasoline d. wax 101. Round each measurement to the number of significant figures indicated in parentheses. a g (3) c L (3) b m (2) d mg (2) 102. Which of the following linear measurements is the longest? a cm c km b mm d nm 103. Helium has a boiling point of 4 K. This is the lowest boiling point of any liquid. Express this temperature in degrees Celsius The density of silicon is 2.33 g/cm 3. What is the volume of a piece of silicon that has a mass of 62.9 g? If You Have Trouble With... Question See Chapter Express the composition of each atom in shorthand form. a. zinc-64 c. hydrogen-3 b. chlorine-37 d. calcium An atom of carbon and an atom of element Z together have a mass of 6 amu less than double the mass of an atom of oxygen. If an atom of oxygen has a mass of 16 amu and the mass of an atom of carbon is 12 amu, what is the mass of an atom of element Z? 107. Determine the number of protons, electrons, and neutrons in each of the three isotopes of oxygen How many orbitals are in the following sublevels? a. 4s sublevel c. 3s sublevel b. 2p sublevel d. 4d sublevel 109. Give the symbol for each element and write the electron configuration for each atom. a. nitrogen c. phosphorus b. beryllium d. potassium 110. An atom of an element has 17 electrons. Give the name and symbol of the element and write the complete electron configuration A beam of electromagnetic radiation has a wavelength of 500 nm. a. What is this wavelength in meters? b. In what region of the spectrum is this? 112. Give the symbol of the element and the complete electron configuration of the element found at each location in the periodic table. a. Group 1A, Period 4 b. Group 3A, Period 3 c. Group 6A, Period 3 d. Group 2A, Period Which subatomic particle plays the most important role in chemistry? 114. Give the name and symbol of two elements that have properties similar to those of potassium. 218 Chapter 7 Assessment