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122ch11c

# 122ch11c - 45 11.65 NaF has the NaCl structure That means...

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45 11.65) NaF has the NaCl structure. That means the F ! ions are in a fcc structure (F ! ions in the corners and on the faces) with the Na + ions between them on the edges and 1 Na + in the body center. Also, the cations and anions touch along an edge so the edge length and ionic radii are related by, R = 2 r + + 2 r ! a) Using ionic radii given in chapter 7 we can estimate the edge length. r Na+ = 1.16 D r F ! = 1.19 D R = 2 r + + 2 r ! = 2 (1.16 D ) + 2 (1.19 D ) = 4.70 D b) In this NaCl structure there are 4 f.u. per unit cell, so there are 4 NaF f.u./u.c. 4 NaF formula units per u.c. (4 Na + and 4 F ! ions) edge length, R = 4.70 D = 4.70 x 10 & 8 cm; FW = 41.988 g/mol D = m x 1/V g 41.988 g NaF 1 mol NiO 4 NaF units 1 u.c. ? ------- = ------------------ x ---------------------------- x ---------------- x ---------------------- cm 3 1 mol NaF 6.02 x 10 23 NaF units 1 u.c. (4.70 x 10 & 8 cm) 3 = 2.6 8 71 g/cm 3 = 2.69 g/cm 3

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46 11.68) a) Cinnabar, HgS, has the ZnS (zinc blende) type structure (Fig. 11.42b). What is density of HgS? 4 HgS formula units per u.c. (4 Hg 2+ and 4 S 2 ! ions) edge length, R = 5.852 D = 5.852 x 10 & 8 cm; FW = 232.6 5 5 D = m x 1/V g 232.6 5 5 g HgS 1 mol HgS 4 HgS units 1 u.c. ? ------- = ------------------- x --------------------------- x ---------------- x ----------------------- cm 3 1 mol HgS 6.022 x 10 23 HgS units 1 u.c. (5.852 x 10 & 8 cm) 3 = 7.71 1 1 g/cm 3 = 7.711 g/cm 3
47 11.68) (cont.) b) Tiemmanite, HgSe, has the ZnS (zinc blende) type structure (Fig. 11.42b).

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122ch11c - 45 11.65 NaF has the NaCl structure That means...

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