Question

An elemental crystal has a density of 8570 kg/m3. The packing efficiency is 0.68. The closest distance of approach between neighbouring atom is 2.86 Å. What is the mass of one atom approximately ?

• A. 29 amu
• B. 39 amu
• C. 63 amu
• D. 93 amu

Answer 1

Answer: (D)

93 amu

Answer 2

The packing efficiency = 0.68, means the given lattice is BCC.

The closest distance of approach = 2r

2r = 2.86 A⁰ = $\frac{\sqrt{3}a}{2}$ or a = $\frac{2 \times 2.86}{\sqrt{3}}$= 3.30 Aº.

Let at. wt. of the element = a

\$\frac{2 \times a}{36 \times 10^{23} \times (3.3)^{3} \times 10^{–24}}$= 8.57

a = 8.57 × 3 × (3.3)³ × 0.1 = 92.39 ~ 93