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The Solid State

Question
CBSEENCH12005512

An element X with an atomic mass of 60 g/mol has density of 6.23 g/cm–3. If the edge length of its cubic unit cell is 400 pm, identify the type of cubic unit cell. Calculate the radius of an atom of this element.

Solution
Solution:
we have given that 
Density, d = 6.23 g/cm3
              a = 400 pm
              M = 60g/mol-1
 
Volume  = (a3)=(400)3 = (400×10-10 cm)3

Z=d×a3×NAM

NAM=6.023×1023 mol-160 g/mol 

Z = 6.023 g cm-3×(400)3×10-30 cm3×6.023×1023 mol-160 g mol-1    = 6.023×64×6.023600   = 2401.49600=4.

Hence, the type of cubic unit cell is FCC


Radius = aa2=40022=2002

              = 2001.414=141.4 pm. 

So radius of element is 141.4 pm