Question

How many lithium atoms are present in unit cell with edge length 3.5 $\stackrel{o}{A}$ 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

Theoretical density of crystal, $\rho =\frac{nM}{N_o{a}^3}g/c{m}^3$

Given $a=3.5\times {10}^{-8}cm,M=6.94g\rho =0.53g/c{m}^3$

$\therefore n=\frac{\rho .N_o.a^3}{M}=\frac{0.53\times 6.022\times {10}^{23}\times (3.5{)}^3\times {10}^{-24}}{6.94}=2$