# 1.25     Aluminium crystallises in a cubic close-packed structure. Its metallic radius is 125 pm.                     (ii) How many unit cells are there in 1.00 cm3 of aluminium?

For cubic close-packed structure,

we have $a=2\sqrt{2} . r$

Given : $r=125 pm$

$a =2\times 1.414\times 125$

$a=354 pm$

the volume of one unit cell $=a^{3}=354^{3}$

$=(354\times 10^{-10})^{3}$

$=4.4 \times 10^{-23} cm^{3}$

Total unit cells in 1.00 cm3$=\frac{total \, \, volume }{size \, \, of\, \, unit\, \, cell}$

$=\frac{1 cm^3}{4.4\times 10^{-23} cm^3}$

$=2.27 \times 1022 unit\, \, cell$

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