In an FCC arrangement of P and Q atoms, P atoms are at the corners of the unit cell, Q - Chemistry - The Solid State

Question

In an FCC arrangement of P and Q atoms, P atoms are at the
corners of the unit cell, Q atoms at the face centres and two atoms
are missing from two corners of each unit cell What is the formula
of the compound?

Priya G N · Accepted Answer

Number of atoms of P at the corners = 6 (because two P are
missing)

Contribution atoms of P towards unit cell = 6 Ã— 1/8 =
6

Number of atoms Q at face-centres = 6

Contribution of atom Q towards unit cell = 6 Ã— 1/2 =
3

Ratio of P : Q = 6/8 : 3 or 3/4 : 3 = 3:12

Therefore the formula of the compound is A3B12

In an FCC arrangement of P and Q atoms, P atoms are at the corners of the unit cell, Q atoms at the face centres and two atoms are missing from two corners of each unit cell. What is the formula of the compound?