2. (23 points) Al adopts an foc unit cell (rai= 143 pm, Aar= 27 g/mol). For Si, in addition fcc positions, half of the tetrahedral holes are filled in. The unit cell parameter, a, for Si is 543 pm (rs=210 pm, Asi=28 g/mol). a. Calculate the density of Al. b. Calculate the atomic packing factor in Si. c. Compare the following for Al and Si: i. Number of atoms per unit cell ii. Planar density for (100) Linear density (LD) = # atoms/distance iii. Linear density for [100] Planar density (PD) = # atoms/area Atomic Packing Factor (APF) = Vstoms/ Vunstcel iv. Atomic packing factor v. Density