a compound made up of elements 'a' and 'b' crystallises in a cpp structure. atoms a present on the corners as well as face centres,whereas atoms b present on the edge centres as well as body centre.what is the formula of the compound?

Hi Ayushman,

Please find below the solution to the asked query:

As we know that, each atom present at eight corners is shared between eight adjacent unit cells, and each atom located at the six faces is shared between two adjacent unit cells, the total number of A atoms in a unit cell will be = $\left(8\times \frac{1}{8}\right)+\left(6\times \frac{1}{2}\right)=1+3=4$

Similarly, each atom at its twelve edges are shared between four adjacent unit cells, and each atom at its body centre wholly belongs to the unit cell, hence the total number of B atoms in the unit cell will be = $\left(12\times \frac{1}{4}\right)+1=3+1=4$

Hence, the formula of the compound is A₄B₄ or simply AB.



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