Question

How many lithium atoms are present in an units cell with edge length $3.5$Å and density $0.53$g $cm^{- 3}$?

(Atomic mass of $Li = 6.94$)

• A. 2
• B. 1
• C. 4
• D. 6

Answer 1

Answer: (A)

2

Answer 2

$d = \frac{Z \times M}{N_{A} \times a^{3}}$

$Z = \frac{a^{3} \times d \times N_{A}}{M}$

$Z = \frac{(3.5 \times 10^{- 8})^{3} \times 0.53 \times 6.023 \times 10^{23}}{6.94} = 1.97 \approx 2$