Copper (Cu) crystal has fcc. (face centred cubic) lattice structure. Atomic mass of copper is `63.5 u`. Find out density of metallic crystal. Atomic radius of copper atom is `127.8` pm.

Explanation

Molar mass of copper, `M=63.5"g mol"^(-1)`
Mass of 1 atom of copper
`=(63.5"g mol"^(-1))/(6.022xx10^(23)"mol"^(-1))`
`=63.5/(6.022)xx10^(-23)g`
`=10.54xx10^(-23)g`
for f.c.c. lattice Z = 4
Mass of 4 unit cell = `4xx10.54xx10^(23)g`
`therefore` No. of unit cells in 12g of copper
`(12g)/(42.18)xx10^(21)=2.84xx10^(-21)`