Question

Copper crystallizes in a face-centered cubic lattice with a unit cell length of $361pm$. What is the radius of copper atom in pm?
(AIPMT -2009)

Answer 1

$Cu\underset{}{\to }fcc\text{lattice}$
along one face:
For fcc
$4r=\sqrt{2}a$

$r=\frac{1}{2\sqrt{2}}a$

$r=\frac{1}{2\sqrt{2}}\times 361=127.65pm\approx 128pm$