Question

Lithium has a $bcc$ structure. Its density is $530 \, kg \, m^{-3}$ and its atomic mass is $6.94 \, g \, mol^{-1}$. Calculate the edge length of a unit cell of Lithium metal. ($NA = 6.02 \times 10^{23} \, mol^{-1}$)

• A. 352 pm
• B. 527 pm
• C. 264 pm
• D. 154 pm

Answer 1

Answer: (A)

352 pm

Answer 2

For BCC $d =\frac{Z\times M}{N_{A} \times a^{3}}$ $530 = \frac{2 \times6.94 \times10^{-3} }{6.02 \times10^{23} \times a^{3}}$ $a^{3} = \frac{2 \times694}{530 \times6.23 \times10^{28}}$ $a^{3} = 0.435 \times10^{-28} m$ $=43.5 \times10^{-30} m$ $= 43500000 pm$ $\therefore a = 352 pm$