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# Chromium Metal Crystallises with a Body Centred Cubic Lattice. the Edge Length Of The Unit Cell is Found to Be 287 Pm. Calculate the Atomic Radius: What Would Be the Density of Chromium in G/Cm3? (Atomic Mass of Cr = 52 ·99) - Chemistry (Theory)

ConceptStates of Matters: Structure and Properties Solid State Calculation of the Number of Atoms per Unit Cell

#### Question

Chromium metal crystallises with a body centred cubic lattice. The edge length of the unit cell is found to be 287 pm. Calculate the atomic radius: What would be the density of chromium in g/cm3? (atomic mass of Cr = 52 ·99)

#### Solution

Given :

Crystal structure of Cr = BCC

Edge length (a) = 287 pm

To find

Density = ρ

Solution:

For BCC crystal system

Edge length (a) = (4r)/sqrt3

:. r = (sqrt3a)/4

= 0.433 x 287 pm

r = 124.27 pm

Now density of a crystal :

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

Where

z = number of atom in BCC unit cell 2

M = Molar mass ofCr =  52.99 g

a^3 = (287 "pm")^3

= (287 xx 10^(-12) m)^3

=(287 xx 10^(-10)cm)^3

= 2.37 xx 10^(-23) cm^3

N_A = 6.022 xx 10^23 atoms

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

= (2 xx 52.99)/(2.37  xx 10^(-23) xx 6.022 xx 10^23)

 = 105.98/14.27

Density of crystal = 7.42 "g/cm"^3

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#### APPEARS IN

2014-2015 (March) (with solutions)
Question 3.1.1 | 2.00 marks
Solution Chromium Metal Crystallises with a Body Centred Cubic Lattice. the Edge Length Of The Unit Cell is Found to Be 287 Pm. Calculate the Atomic Radius: What Would Be the Density of Chromium in G/Cm3? (Atomic Mass of Cr = 52 ·99) Concept: States of Matters: Structure and Properties Solid State - Calculation of the Number of Atoms per Unit Cell.
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