Question
Sat September 01, 2012 By: Lekha
 

In a solid AB having the NaCl structure A atom occupies the corners of cubic unit cell.if all the face centred atoms along one of the axes are removed then the resultant stoichiometry of the solid is?

Expert Reply
Sun September 02, 2012
According to the structure of NaCl 
Here, 'A'  will occupy 8 corners of  cubic unit cell which will contribute 1/8 each to the cube
therefore 8*1/8 = 1
and 6 face centered atoms will contribute 1/2 to the cube
hence 6*1/2=3
Therefore total contribution of atom'A' is  3+1=4
Now B occupies octahedral voids (NaCl structure)  which contributes 1/4
therefore 1+12*1/4 = 4
So the formula is A A4B4 or AB
Now  we are removing all  face centered atoms along one axis
so the number of atoms removed from cube are 2
so contribution from 'A' remains 8*1/8(corner atoms) + 4*1/2(facecentered atoms) = 3
so the resultant becomes A3B4
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