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Niobium crystallises in body-centred cubic structure. If density is 8.55 g cm−3, calculate atomic radius of niobium using its atomic mass 93 u. - CBSE (Science) Class 12 - Chemistry

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ConceptPacking Efficiency Efficiency of Packing in Body-centred Cubic Structures

Question

Niobium crystallises in body-centred cubic structure. If density is 8.55 g cm−3, calculate atomic radius of niobium using its atomic mass 93 u.

Solution

It is given that the density of niobium, d = 8.55 g cm−3

Atomic mass, M = 93 gmol−1

As the lattice is bcc type, the number of atoms per unit cell, z = 2

We also know that, NA = 6.022 × 1023 mol−1

Applying the relation:

d = (zM)/(a^3N_A)

=>a^3= (zM)/(dN_A)

= (2xx93 gmol^(-1))/(8.55 "gcm"^(-3)xx6.022xx10^(23) mol^(-1))

= 3.612 × 10−23 cm3

So, a = 3.306 × 10−8 cm

For body-centred cubic unit cell:

r = sqrt3/4a

=sqrt3/4xx3.306xx10^(-8) cm

= 1.432 × 10−8 cm

= 14.32 × 10−9 cm

= 14.32 nm..

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Solution Niobium crystallises in body-centred cubic structure. If density is 8.55 g cm−3, calculate atomic radius of niobium using its atomic mass 93 u. Concept: Packing Efficiency - Efficiency of Packing in Body-centred Cubic Structures.
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