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Unformatted text preview: MAT 33 Fall 2008 Homework # 3 - Solutions Due: 09/15/08 1.) On the basis of ionic charge and ionic radii, predict the crystal structures for the following materials: i) CsI, ii) NiO, iii) KI, iv) NiS Justify your choices. 2.) Calculate the theoretical density of MgO, given that it is isostructural with rocksalt. The atomic weights of Mg and O are 24.31g/mol and 16g/mol respectively. The ionic radii of Mg 2+ and O 2- are 0.072nm and 0.140nm respectively. MgO adopts the NaCl type crystal structure Volume V c of the MgO unit cell = a 3 = (2r Mg2+ + 2r O2- ) 3 Number of formula units per unit cell, n, = 4 = n ( A c + A A ) (Equation 3.6 Callister) V c N A 3.) Calculate the ionic packing factor for CsCl. The ionic radii are 0.170 nm and 0.181 nm for Cs + and Cl- , respectively. From the ratio of ionic radii, r c /r a = 0.170/0.181 = 0.94, CsCl is found to have eightfold ( i.e. cubic) co-ordination. The ions touch each other across the cube diagonal of the CsCl unit cell. Let r = radius of the Cs + ion and R = radius of the Cl- ion....
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This note was uploaded on 02/10/2009 for the course MAT 33 taught by Professor Keith during the Spring '07 term at Lehigh University .
- Spring '07