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  • Stuck here, help me understand: If distance between Na+ and Cl- ions in NaCl crystal is 'a' pm , what is the length of the cell edge ?

If distance between Na+ and Cl- ions in NaCl crystal is 'a' pm , what is the length of the cell edge ?

  • Option 1)

    2a pm

  • Option 2)

    4a pm

  • Option 3)

    \frac{a}{2}\ pm

  • Option 4)

    \frac{a}{4}\ pm

 

Answers (1)

best_answer

Edge length in NaCl structure =2\left ( r_{Na^{+}}+r_{Cl^{-}} \right )

r_{Na^{+}}+r_{Cl^{-}} =a

Edge length in NaCl structure = 2a

 

 

Rock salt structure or NaCl type structure -

Cl^{-} located at all corners and face centre

Na^{+} located at all octahedral voids

Edge length = 2 ( r_{Na^{+}} + r_{Cl^{-}} )

Coordination number = 6:6

- wherein

Total number of Cl^{-} = 4

Total number of Na^{+} = 4

Total number of NaCl molecule per unit cell = 4

Ex : halides of  K^{+} , Na^{+} , Rb^{+} and FeO

 

 


Option 1)

2a pm

This is correct

Option 2)

4a pm

This is incorrect

Option 3)

\frac{a}{2}\ pm

This is incorrect

Option 4)

\frac{a}{4}\ pm

This is incorrect

Posted by

divya.saini

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