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CHAPTER 9 MODELS OF CHEMICAL BONDING 9.1 a) Larger ionization energy decreases metallic character. b) Larger atomic radius increases metallic character. c) Larger number of outer electrons decreases metallic character. d) Larger effective nuclear charge decreases metallic character. 9.2 The tendency of main-group elements to form cations decreases from Group 1A(1) to 4A(14), and the tendency to form anions increases from Group 4A(14) to 7A(17). 1A(1) and 2A(2) elements form mono- and divalent cations, respectively, while 6A(16) and 7A(17) elements form di- and monovalent anions, respectively. 9.3 A has covalent bonding, B has ionic bonding, and C has metallic bonding. 9.4 Metallic behavior increases to the left and down on the periodic table. a) Cs is more metallic since it is further down the alkali metal group than Na. b) Rb is more metallic since it is both to the left and down from Mg. c) As is more metallic since it is further down Group 5A than N. 9.5 a) O b) Be c) Se 9.6 Ionic bonding occurs between metals and nonmetals and covalent bonding between nonmetals. a) Bond in CsF is ionic because Cs is a metal and F is a nonmetal. b) Bonding in N 2 is covalent because N is a nonmetal. c) Bonding in H 2 S( g ) is covalent because both H and S are nonmetals. 9.7 a) covalent b) covalent c) ionic 9.8 Lewis electron-dot symbols show valence electrons as dots. Place one dot at a time on the four sides (this method explains the structure in b) and then pair up dots until all valence electrons are used. Rb Si I a) b) c) 9.9 a) b) c) Kr Ba Br 9.10 a) Assuming X is an A-group element, the number of dots (valence electrons) equals the group number. Therefore, X is a 6A(16) element with 6 valence electrons. Its general electron configuration is [noble gas]n s 2 n p 4 , where n is the energy level. b) X has three valence electrons and is a 3A(13) element with general e configuration [noble gas]n s 2 n p 1 . 9.11 a) 5A(15); n s 2 n p 3 b) 4A(14); n s 2 n p 2 9.12 Energy is required to form the cations and anions in ionic compounds but energy is released when the oppositely charged ions come together to form the compound. This energy is the lattice energy and more than compensates for the required energy to form ions from metals and nonmetals. 9-1
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9.13 a) Because the lattice energy is the result of electrostatic attractions among the oppositely charged ions, its magnitude depends on several factors, including ionic size, ionic charge, and the arrangement of ions in the solid. For a particular arrangement of ions, the lattice energy increases as the charges on the ions increase and as their radii decrease. b) Increasing lattice energy: A < B < C . The ions in A have +1 and –1 charges while the charges of the ions in B and C are +2 and –2. The smaller ion charges in A result in the lowest lattice energy. The ions in B have a larger radius than the ions in C. The larger radii results in a lower lattice energy for B than for C.
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