If three elements P, Q and R crystallise in a cubic solid lattice with Patoms at the corners, Q atoms at the cube centres and R atoms at the centre of the edges, then write the formula of the compound.
Solution: As P atoms are present at the 8 corners of the cube. Therefore,
No. of P atoms in the unit cell = 8 x 1/8 = 1
Q atoms are present at the cube centres, No. of Q atoms in the unit cell = 1
R atoms are present at the edges. Since there are 12 edges and atom at each edge is shared by four atoms.
Therefore,
No. of R atoms in the unit cell = 12 x 1/4 = 3
The formula of the compound = PQR3
