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Simple Solids - Structures

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1. Draw one layer of close-packed spheres. On this layer mark the positions of the centers of the B layer atoms using the symbol X and, with the symbol O mark the positions of the centers of the C layer atoms of an fcc lattice.

2. Consider the structure of rock salt. (a) What are the coordination numbers of the anion and cation? (b) How many Na+ ions occupy second-nearest neighbor locations of an Na+ ion? (c) Pick out the closest-packed plane of CI- ions. (Hint: this hexagonal plane will be perpendicular to a threefold axis).

3. Consider the structure of cesium chloride. (a) What is the coordination number of the anion and cation? (b) How many Cs+ ions occupy second-nearest neighbor locations of a Cs+ ion?

4. (a) How many Cs+ ions and how many CI- ions are in the CsCI unit cell? (b) How many Zn2+ ions and how many S2- ions are in the sphalerite unit cell?

5. Given the following data for the length of a side of the unit cell for compounds "that crystallize in the rock-salt structure, determine the cation radii: MgSe (5.45 A). CaSe (5.91A). SrSe (6.23 A), BaSe (6.62 A.). (To determine the Se2- radius, assume that the Se2- ions are in contact in MgSe).

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The solution provides a written response to these questions of compounds' structure and shape, augmented with illustrative diagrams of the molecules in question and tables of the results derived for clarity.

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Packing of Particles in Solids-space Lattices

Hexagonal Closet Packaging vs. Cubic Closet Packaging (face-centered) vs. Body-centered

a) Which of the three types of packaging has the least efficient arrangement of atoms? Justify the answer.

b) How do the two more efficient forms of packing compare regarding volume?

c) What is the relationship between coordination number, packing, and density (as mass/volume).

d) State the coordination number of each type of packing, i.e., what is the number of neighbours touching each atom in an infinite array of space lattices?

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