Solutions: Chapter 7

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© Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Section 7.2 Part A Completion 1. electrostatic forces 2. oppositely 3. ionic bonds 4. neutral 5. formula unit 6. crystals 7. high 8. large 9. stable 10. molten Part B True-False 11. AT 13. AT 15. NT 12. ST 14. ST Part C Matching 16. b 18. c 20. a 17. e 19. d Part D Questions and Problems 21. Ionic bonds are the electrostatic forces of attraction that bind oppositely charged ions together. In an ionic compound, the positive charges of the cations equal the negative charges of the ions. 22. When ionic compounds are melted, the orderly crystal structure breaks down. Each ion is then free to move throughout the molten mass. If a voltage is applied, cations will migrate to one electrode, and anions will migrate to the other. This movement of ions means that there is a flow of electricity between the two electrodes. When ionic compounds dissolve in water, their ions are free to move. Thus, aqueous solutions of ionic compounds also conduct electricity. Section 7.3 Part A Completion 1. cations 2. electrons 3. metallic 4. electrical 5. malleable/ductile 6. ductile/malleable 7. body-centered/face-centered 8. face-centered/body-centered 9. hexagonal close-packed 10. alloy Part B True-False 11. NT 13. NT 15. AT 12. ST 14. AT Part C Matching 16. d 18. b 20. a 17. e 19. c Part D Questions and Problems 21. Solid metals consist of closely packed cations surrounded by free-moving valence electrons, which make metals good conductors of electric current. As electrons enter one end of a bar of metal, an equal number leave the other end. Metal cations are insulated from one another by electrons. When a metal is subjected to pressure, the metal cations easily slide past one another. This behavior makes the metal malleable and ductile. 22. The superior properties of alloys result from the cumulative properties of all the constituents of the alloy. For example, an alloy can be more durable than one constituent but more malleable than another. Practice Problems 7 Section 7.1 1. a. (i) 2 (ii) Ba 6 (iii) Ba 2 b. (i) 7 (ii) (iii) I c. (i) 1 (ii) K = (iii) K I 2. a. 3 b. 7 c. 6 3. a. 1s22s22p63s23p64s2 b. 1s 2 2s 2 2p 6 3s 2 3p 5 c. 1s 2 2s 2 2p 6 d. 1s 2 2s 2 2p 6 3s 2 3p 6 e. 1s 2 2s 2 2p 6 4. The number of valence electrons in an atom of a representative element is the same as the group number of the element. Answer Key 781
5. a. loses 2 electrons; cation b. loses 3 electrons; cation c. gains 2 electrons; anion d. loses 1 electron; cation e. gains 1 electron; anion f. gains 3 electrons; anion 6. a. chloride ion, Cl b. potassium ion, K c. oxide ion, O 2 d. barium ion, Ba 2 7. a. 2 lost b. 1 gained c. 1 lost d. 3 lost 8. a. cation d. anion b. cation e. cation c. anion f. cation Section 7.2 1. a. NaBr d. Al 2 O 3 b. Na 2 S e. BaCl 2 c. CaI2 2. Ionic compounds are formed when metals react with nonmetals. The combinations in b and c will form ionic compounds 3. The coordination number is the number of ions of the opposite charge that surround an ion in a crystal. 4. The coordination number is determined by using x-ray diffraction crystallography. Patterns are used to calculate the positions of ions in the crystal and to define the structure of the crystal. Section 7.3 1. A metallic bond is made up of cations that are surrounded by mobile valence electrons. 2. The metallic crystal is thought to consist of an array of metal cations in a “sea” of electrons. Although the electrons are attracted to the metal cations, no individual electron is confined to any specific cation; rather, the electrons are free to move about the crystalline structure. When electrical current is applied to a metal, these mobile electrons can carry charge from one end of the metal to the other. 3. Metals are crystalline. The metal cations are arranged in a very compact and orderly structure or pattern. 782 Core Teaching Resources 4. • Body-centered cubic: every atom (except those at the surface) has 8 neighbors. • Face-centered cubic: every atom has 12 neighbors. • Hexagonal close-packed: every atom has 12 neighbors, but in a different arrangement than face-centered cubic. 5. An alloy is a mixture of two or more elements, at least one of which is a metal. Alloys have properties of metals. 6. a. Brass: copper and zinc b. Bronze: copper and tin c. Stainless steel: iron, chromium, carbon, and nickel d. Sterling silver: silver and copper e. Cast iron: iron and carbon f. Spring steel: iron, chromium, and carbon Interpreting Graphics 7 1. sodium 1s22s22p63s1 Sodium has 1 valence electron. chlorine 1s22s22p63s23p5 Chlorine has 7 valence electrons. 2. In Step 1, each sodium atom gives up one valence electron to a chlorine atom. In this process, sodium becomes positively charged and chlorine becomes negatively charged. Each ion attains the electron configuration of the nearest noble gas. 3. In Step 2, ionic bonds form between sodium cations and chlorine anions. The ions arrange themselves in an orderly, three-dimensional array characteristic of a crystalline solid. In NaCl, each ion is surrounded by six other ions of opposite charge, which results in a very stable ionic compound. 4. NaCl is typical of many ionic compounds. The large amount of energy released when an ionic lattice is formed (Step 2) compensates for the endothermic nature of the electron transfer (Step 1). To reverse the lattice formation through melting would require enough energy to overcome the multiple atttractions within the crystal lattice. Vocabulary Review 7 1. j 6. l 11. b 2. i 7. a 12. k 3. f 8. c 13. m 4. g 9. e © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.
Page 1: 33. a. K; Li; K b. C; F; C c. Ca; M

Solutions: Chapter 7

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