Platinum (atomic radius `= 1.38 Å`) crystallises in a cubic closed packed structure. Calculate the edge length of the face-centred cubic unit cell and the density of the platinum (Pt = 195)

Explanation

`r = (a)/(2sqrt2)` (for fcc), `a = 2 sqrt2 r = 3.9 Å`
Density `= (ZM)/(a^(3)N_(0)) = (4 xx 195)/((3.9 xx 10^(-8))^(3) xx 6.023 xx 10^(23)) = 21.83 g//cm^(3)`