Gold (atomic mass = 197 u) has atomic radius = 0.144 nm. It crystallises in face centred unit cell. Calculate the density of gold. (No = `6.022xx10^(23)mol^(-1))`

Explanation

For fcc unit cell , `r=a/(2sqrt2)` or `a=2sqrt2 r=2xx1.414 xx 0.144`nm = 0.407 nm =`0.407xx10^(-7)` cm
`rho=(ZxxM)/(a^3xxN_0)=(4xx197 "g mol"^(-1))/((0.407xx10^(-7)cm)^3 xx (6.02xx10^23 mol^(-1)))=19.4 g cm^(-3)`