211chp8

# 211chp8 - Chapter 8 Homework Solutions 11 a Al 16 a BaF2 b...

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11/8/11 11. 16. a) BaF 2 b) CsCl c) Li 3 N d) Al 2 O 3 18. a) [Ar] 3 d 10 d) [Kr] 4 d 6 b) [Kr] 5 s 2 4 d 10 5 p 6 e) [Xe] 6 s 2 4 f 14 5 d 10 c) [Ar] f) [Xe] 6 s 2 4 f 14 5 d 10 (b) and (c) have noble gas configurations. 21. The lattice energies of these salts are KF (808 kJ/mol), CaO (3414 kJ/mol), ScN (7547 kJ/mol). To answer this problem you need the equation that describes the energy relationship between ions and their separation (see page 305). First, the charges on the ions in KF are ± 1, on the ions in CaO ± 2, and on the ions in ScN ± 3. If the interionic distances are the same, then the energy of attraction in CaO should be 4 times that in KF (3232 kJ/mol), while the corresponding energy in ScN should be 9 times larger (7272 kJ/mol). The actual values are amazing close to the calculated values, but a little larger suggesting that the ions in the more highly charged salts are also separated by a slightly smaller distance than the ions in KF (which is true). 24. Remember the equation: E = k ( )( ) cation charge anion charge distance of separation Lattice energy increases as ion charges increase and/or as their distance of separation decreases. Thus: a) The anions in both cases are the same and both cations have a +2 charge, so the difference is the size of the cations. Calcium ion is smaller than barium ion so the chloride can approach closer. This provides a higher lattice energy. b) Sodium ion is smaller than rubidium ion which is smaller than cesium ion. Chloride is smaller than bromide. c) Barium ion (+2) has a higher charge than potassium ion (+1). Oxide (-2) has a larger negative charge than fluoride (-1). That barium ion is larger than potassium ion and oxide is larger than fluoride partially offsets the charge, but does not override them. 30. Potassium is unlikely to form covalent bonds because it has a very low electron affinity and ionization energy. Therefore, it gives up its valence electron relatively easily and has a very low tendency to draw the electrons of other atoms to itself. Argon is unlikely to form covalent bonds because it has a complete valence shell and therefore neither needs additional electron density nor has any tendency to give it up (high IE & zero EA). a)

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## This note was uploaded on 02/12/2012 for the course CHM 211 taught by Professor Staff during the Fall '08 term at Marshall.

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211chp8 - Chapter 8 Homework Solutions 11 a Al 16 a BaF2 b...

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