Question

9. Hypothesize why a compound would adopt a body-centered cubic unit cell when it crystallizes versus a face-centered cubic. 10. Calculate the edge length of a simple cubic unit cell composed of polonium atoms. The atomic radius of polonium is 167 pm. 11. Calculate the density in g/cm3 of platinum if the atomic radius is 139 pm and it forms a face- centered unit cell.

Answer 1

9. F.C.C has a higher packing frequency about 74% rather than B.C.C lattice.

When a compound crystallizes to BCC rather than F.C.C it loses lower energy.

10.

Saturday a = 28 The edge length of a simple cabic unit cell of po atoms. The radius of Po atoms = 167pm a = 2x 167 = 334 pm . The edge length is 334pm 04 Sunday

11.

PIL 18 19 20 21 22 23 24 25 26 27 28 29 30 31 E T W T F S S M T W T F S S M T W T 14th Week -096-269 Friday We know that - MZ 8 BNA fa density M- Moleculars Weight of atom 7. The na of atoms in a unit cell a. The edge length of unit cell NA = 6.023 x 1023 Here - 4 for f.ee lattice to V2 a = 45 or, a= 48 - 4x 139x10 12 V2 NA= 6.023x10 23 cm = 3.93 x 108 cm M= 195 Hence, the cm density 195x4 o 73.42x16-8) 3x6023 xlo23 = 21.3 gm/ cm3