1. Gold exhibits a face-centered cubic unit cell that is 4.08 A on a side. Estimate gold’s density, in g/cm 3. D = m V = 4 atoms (197.0 amu/at.) (4.08 A) 3 = 1.16 x 10 25 1x10 –8 cm amu cm 3 ( 1 g 6.02 x 10 23 amu ) = 19.3 g cm 3

2. close-packed layer. Roughly equal-sized spheres, such as those in metallic solids, are arranged in one of several configurations. These configurations are collectively called the close packing of spheres. -- In a given layer, the atoms are arranged such that each atom in that layer is surrounded by six others. This is called a...

3. ------ C cubic close packing hexagonal close packing Name of Pattern ------ A 1 (bottom) ------ B 2 ------ A 3 ------ B 4 (top) close-packed layer position close-packed layer position Layer Number ** Cubic close packing is equivalent to the face-centered cubic unit cell. (HCP)(CCP/FCC)

4. HCP: The coordination number for a packing pattern is equal to the number of equidistant, nearest neighbors for any atom within the matrix. -- for particular packing arrangements: CCP/FCC: BCC:P/SC: 12 86 X X X X For unequal-sized spheres, sometimes the larger spheres assume a close-packed arrangement, and then the smaller particles fit into the spaces in between.