Question

an element ' X' ( Atomic mass = 40 g / mol ) having f.c.c. structure,has unit cell edge length of 540 pm.Calculate the density of 'X'

Answer 1

density= (Z × MOLECUALR MASS) / ( edge length^3 × Avogadro no. )


also, atomic mass = (Mol. mass)/(Avogadro no.)

therefore new modified formula as per the question is,
density= (Z × atomic mass ) / (edge length)^3

for FCC, Z= 8×1/8+1/2×6 = 4


on substituting the values
density = 4 × 40g/ (540×10^-12m)^3
= 306.96 g/m^3