Na and Mg crystallize in bcc and fcc type crystals respectively, then the number of atoms of Na and Mg present in the unit cell of their respective crystal is

  • Option 1)

    4 and 2

  • Option 2)

    9 and 14

  • Option 3)

    14 and 9

  • Option 4)

    2 and 4.

 

Answers (2)

As we learnt in

z for body centered unit cell -

Lattice points: at corners and body center of unit cell.

For body centered cubic (BCC), z=2

- wherein

 

 

No. of atoms(z) for face centered unit cell -

Lattice points: at corners and face centers of unit cell.

For face centered cubic (FCC), z=4.

- wherein

 

 

 

bcc - Points are at corners and one in the centre of the unit cell.

Number of atoms per unit cell = 8\times \frac{1}{8}+1= 2

fcc - Points are at the corners and also centre of the six faces of each cell.

Number of atoms per unit cell = 8\times \frac{1}{8}+6\times \frac{1}{2}= 4

Correct option is 4.


Option 1)

4 and 2

This is an incorrect option.

Option 2)

9 and 14

This is an incorrect option.

Option 3)

14 and 9

This is an incorrect option.

Option 4)

2 and 4.

This is the correct option.

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