Question

Copper crystallises in fcc lattice with a unit cell edge of 361 pm. The radius of the copper atom is :

• A. 157 pm
• B. 181 pm
• C. 108 pm
• D. 128 pm

Answer 1

The correct option is D 128 pm

As given that copper crystallizes is FCC lattice (Face centred cubic). In FCC atoms are present on the corners of the cubic, unit cell as well as on the face centres of each face.

The atoms on the face diagonal will be touching each other. Let, the radius of the atom be $r$ and edge length of the cube be $a$.

Face diagonal of cube $=\sqrt{2}a$

$\Rightarrow r+2r+r=\sqrt{2}a$

$\Rightarrow r=\frac{\sqrt{2}a}{4}=\frac{a}{2\sqrt{2}}=\frac{361}{2\sqrt{2}}pm=128pm$

Therefore, the option is D.