Gold (atomic radius = 0.144 nm) crystallises in a face-centred uinit cell. What is the length of a side of the cell ?
For a face - centred cubic unit cell (fcc)
We know, for a fcc unit cell,radius of atom
r = a2√2
Edge length (a)=2 √2 r
=2 ×1.4142 ×0.144 nm
= 0.407 nm