Question

A simple binary compound MmXn, is known to have a structure of ccp anions with all of the Td (tetrahedral) holes filled with M cations. What is the empirical formula of this compound?

Using real elements in place of M and X what would be a possible chemical formula for the compound?

Answer 1

in CCP total 4 atoms present in one unit cell.   so   anions = 4 (X =4)

in any unit cell       tetrahedral holes   = 2 x number of atoms in unit cell

                                              Td holes = 2 x 4 = 8

so total   8 cations present    M = 8

so       M : X = 8 : 4 = 2 : 1

formula =   M₂ X₁