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 number of P and Q?

Explanation

Number of Q atoms per unit cell = `8xx1/8=1`
P-atom is at the body centre of the unit cell and hence its contribution to one unit cell = 1. Therefore, number of P-atom per unit cell = 1. Ratio of the number of P and Q atoms per unit cell, P : Q = `1:1`.
`therefore" "` Formula of the compound: PQ
Each Q atom is in contact with six nearest neighbour Q atoms. Hence, its coordination number = 6. P atom is in contact with eight nearest neighbour Q atoms. Hence, its coordination number = 8.