Question:
Gold (atomic radius = 0.144 nm) crystallises in a face-centred unit cell. What is the length of a side of the cell?
Solution:
For a face-centred unit cell:
$a=2 \sqrt{2} r$
It is given that the atomic radius, r = 0.144 nm
So, $a=2 \sqrt{2} \times 0.144 \mathrm{~nm}$
= 0.407 nm
Hence, length of a side of the cell = 0.407 nm
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