Question

They metal crystallizes in a face center cubic lattice. The radius of the atom is 196 PM and the density of the element is 1.55 g/cm3. How many atoms are there per unit cell?

Answer 1

r    = 196pm

     = 196*10^-10 cm

a   = 22 r

    = 2*1.414*196*10^-10

= 5.54*10^-8 cm

d = 1.55g/cm^3

d   = ZM/Na^3

In face centered cubic unit cell has 8 atoms at the corner .Each corner atoms share 8 unit cells.1/8 of the atom belongs to cell.

6 atoms are present in facc. Each face atom share two units.

1/2 of the atom belongs to cell.

8*1/8 + 6*1/2 = 4 atoms

FCC contains 4 atoms >>>>answer