Question

An element crystallizes in a fcc lattice with cell edge 250 pm. Calculate the density if 300 g of this element contain 2 x 10²⁴ atom.

Answer 1

a = 250 pm = 250 x 10^-12 m = 250 x 10^-10 cm 2 x 10²⁴ atom weighs = 300 g

Answer 2

We know that the unit cell of a FCC lattice contains 4 atoms.

Given 2*10^24 atoms weigh 300g

So mass of the unit cell m =(4*300)/(2*10^24)g

Length of the edge of the FCC unit 

a= 250pm=250*10^10cm

Density of the lattice d=m/a^3

=38.4gcm^-3