Question

In an ccp arrangement of A and B atoms ,A is present at the corners as well as face centres of the unit cell and B at its edge centres as well as body centres..If one atom of A is missing from its position at the corners,what is the formula of the compound?

Answer 1

A:  in one cubic cell:  8 corners * 1/8  + 1/2  * 6 faces = 4 atoms
B :   1/4 * 12 edges + 1 center = 4 atoms.
So the formula for ccp arrangement with no atoms missing:  A4 B4

1)
If one atom of A is missing from the face center :
         8 corners * 1/8 + 1/2 * 5 faces = 7/2  in one cell
So  Formula is:   A_7/2  B_4  or    A7 B8

2) If one atom of A is missing from the corner of a cell:
           we have 7/8 + 1/2*6 = 31/8 atoms in a cell.
      Formula :   A_31/8   B_4          or   A31  B32