6 face-centered atoms X 1 / 2 per unit cell = 6 X 1 / 2 = 3 atoms Total number of atoms per unit cell
= 4 atoms
In solids, these constituent particles are closely-packed that leaves minimum vacant space.
Question: An element with molar mass 2.7 × 10-2 kg mol-1 forms a cubic unit cell with edge length 405 pm. If its density is 2.7 × 10 3 kg-3, what is the nature of the cubic unit cell?
Answer: d = 2.7 × 10 3 kg-3 M = 2.7 × 10-2 kg mol-1 a = 405 pm = 405 X 10-12
NA = 6.023 X 10 23
Using the formula
Z = 4 Unit cell is fcc unit cell. Volume of 54 g of the element = 0.054 /( 2.7X10 3) = 2 X 10-6
Number of unit cell in this volume = volume of 554 g of element / volume of each unit cell = 2 X 10-6 /( 405 X 10-12) 3 = 3.012 X 10 22
Question: Copper crystallises into a fcc lattice with edge length 3.61 x 10-
8 cm. Show that the calculated density is in agreement with its measured value of 8.92 g cm-3
Answer: Given that Copper crystallises into a fcc lattice