Homework 3 key

Homework 3 key - Chemistry 3301 - Descriptive Inorganic...

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Spring Semester 2009 Homework 3 Key (1) Using radius ratios and an ionic model, suggest a probable structure for each of the following crystalline compounds. Write the radius ratio and the expected coordination number of the cation (4, 6, or 8), and give the expected structural type (sodium chloride, cesium chloride, zinc blende, wurtzite, fluorite, nickel arsenide, or rutile). The structures are described on pp. 214 – 217 in Miessler & Tarr. Use the values for ionic radii listed in Appendix B-1 on pp. 668 - 671 in Miessler & Tarr. (a) BeO Ion 2-coord radius 4-coord radius 6-coord radius 8-coord radius Be 2+ 41 59 O 2- 121 124 126 128 The compound has equal numbers of Be 2+ ions and O 2- ions, so the coordination number will be the same for both, i.e. 4:4, 6:6, 8:8. Radius ratios: 4:4 is (41/124) = 0.33 6:6 is (59/126) = 0.47 8:8 is (?/128). Estimate an 8-coordinate radius for Be 2+ 8:8 is about (77/128) = 0.60 The 4:4 radius ratio is definitely in the 4-coordinate region (less than 0.414). The 6:6 radius ratio is in the low end of the 6-coordinate region (between 0.414 and 0.732). The 8:8 radius ratio is definitely NOT in the 8-coordinate region (above 0.732). The 4-coordinate structure is most likely. There are two possible 4:4 structures: zinc blende and wurtzite. Answer:
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Homework 3 key - Chemistry 3301 - Descriptive Inorganic...

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