Question

Al (atomic weight = 27) crystallizes in the cubic system with a cell edge of 4.05AA. Its density is 2.7g cm⁻3. Determine the unit cell type and radius of the Al atom.

• A. fcc, 2.432AA
• B. bcc, 2.432AA
• C. bcc, 1.432AA
• D. fcc, 1.432AA

Hint:

Aluminium crystallizes in fcc structure.

Answer 1

The Correct Option is D

Step 1: For fcc lattice, number of atoms per unit cell Z=4.
Step 2: Relation between radius and edge length: r=fraca√(2)4
Step 3: Substituting a=4.05AA: r=(4.05×1.414)/(4)≈1.432AA