ï»¿ 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? from Chemistry The Solid State Class 12 Nagaland Board

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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?

Formula of a compound is same as the formula of unit cell. An atom at the corner of cube contributes only l/8th to the unit cell and there are 8 corners in a cube.
∴  No. of atoms of Q in the unit cell

An atom at centre of cube belongs only to this unit cell and there is only one body centre in the unit cell.
∴   No. of atoms of P in the unit cell = 1 x 1 = 1
Thus, the formula of compound is PQ or QP.
For body centred cubic unit cell, the coordination number is 8:8.
∴ Co-ordination number P = 8 and also coordination number of Q = 8.

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