Question

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

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

Answer 1

Answer: (A)

For BCC
$d=\frac{Z\times M}{N_A\times a^3}$
$530=\frac{2\times 6.94\times 10^{-3}}{6.02\times 10^{23}\times a^3}$
$a^3=\frac{2\times 694}{530\times 6.23\times 10^{28}}$
$a^3=0.435\times 10^{-28}m$
$=43.5\times 10^{-30}m$
$=43500000pm$
$\therefore a=352pm$