Question

A cubic solid is made of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body-centre. What is the formula of the compound? What are the coordination numbers of P and Q? 

Answer 1

It is given that the atoms of Q are present at the corners of the cube.

Therefore, number of atoms of Q in one unit cell =8x1/8=1

It is also given that the atoms of P are present at the body-centre.

Therefore, number of atoms of P in one unit cell = 1 

This means that the ratio of the number of P atoms to the number of Q atoms, P:Q = 1:1 

Hence, the formula of the compound is PQ. The coordination number of both P and Q is 8.