Question

Molybdenum forms bcc crystal at 20 degree celcius it has debsity 10.3gm/cc. What is the distance between the centres of the nearest molybdenum atoms

Answer 1

Answer: 135.5pm

In a body-centred cubic unit cell,there are two atoms per unit cell.Hence,from the expression

r=Na3(MNA)r=Na3(MNA)

We get a3=Nρ(MNA)=(210.3gcm−3)(95.94gmol−16.023×1023mol−1)a3=Nρ(MNA)=(210.3gcm−3)(95.94gmol−16.023×1023mol−1)=3.09×10−23cm3=3.09×10−23cm3

a=3.13×10−8cm=313a=3.13×10−8cm=313pm