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plane for the rock salt crystal structure, (b) (110) plane for the cesium chloride crystal structure, (c) (111) plane for the zinc blende crystal structure, and (d) (110) plane for the perovskite crystal structure.

3.66 The zinc blende crystal structure is one that may be generated from close-packed

planes of anions.

(a) Will the stacking sequence for this structure be FCC or HCP? Why?

(b) Will cations fill tetrahedral or octahedral positions? Why?

(c) What fraction of the positions will be occupied?

3.81* The metal iridium has an FCC crystal structure. If the angle of diffraction for

the (220) set of planes occurs at 69.22° (first-order reflection) when monochromatic x-radiation having a wavelength of 0.1542 nm is used, compute (a) the interplanar spacing for this set of planes, and (b) the atomic radius for an iridium atom.

4.10 What is the difference between configuration and conformation in relation to

polymer chains? vinyl chloride).

4.22 (a) Determine the ratio of butadiene to styrene mers in a copolymer having a

weight-average molecular weight of 350,000 g/mol and weight-average degree of polymerization of 4425.

(b) Which type(s) of copolymer(s) will this copolymer be, considering the following possibilities: random, alternating, graft, and block? Why?

4.23 Crosslinked copolymers consisting of 60 wt% ethylene and 40 wt% propylene

may have elastic properties similar to those for natural rubber. For a copolymer of this composition, determine the fraction of both mer types.

4.25 (a) Compare the crystalline state in metals and polymers. (b) Compare the

noncrystalline state as it applies to polymers and ceramic glasses.

4.26 Explain briefly why the tendency of a polymer to crystallize decreases with

increasing molecular weight.

4.27* For each of the following pairs of polymers, do the following: (1) state whether

or not it is possible to determine if one polymer is more likely to crystallize than the other; (2) if it is possible, note which is the more likely and then cite reason(s) for your choice; and (3) if it is not possible to decide, then state why.

(a) Linear and syndiotactic polyvinyl chloride; linear and isotactic polystyrene. (b) Network phenol-formaldehyde; linear and heavily crosslinked cis-isoprene. (c) Linear polyethylene; lightly branched isotactic polypropylene.

(d) Alternating poly(styrene-ethylene) copolymer; random poly(vinylchloride-tetrafluoroethylene) copolymer.

4.28 Compute the density of totally crystalline polyethylene. The orthorhombic unit

cell for polyethylene is shown in Figure 4.10; also, the equivalent of two ethylene mer units is contained within each unit cell.

5.11 What point defects are possible for MgO as an impurity in Al2O3? How many

Mg 2+ ions must be added to form each of these defects?

5.13 What is the composition, in weight percent, of an alloy that consists of 6 at% Pb

and 94 at% Sn?

5.14 Calculate the composition, in weight per-cent, of an alloy that contains 218.0 kg

titanium, 14.6 kg of aluminum, and 9.7 kg of vanadium.

5.23 Gold forms a substitutional solid solution with silver. Compute the number of

gold atoms per cubic centimeter for a silver-gold alloy that contains 10 wt% Au and 90 wt% Ag. The densities of pure gold and silver are 19.32 and 10.49 g/cm