. 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


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?
 
Hint :   The formula of a compound represents the ratio of number of different atoms present in the compound, so
 
            (i)   Find the number of Q atoms per unit cell (as each corner is shared by 8 unit cells).
 
            (ii) Find the number of P atoms per unit cell (as body centre atom is not shared by any other unit cell).
 
            (iii) Find the ratio of P and Q and formula of compound.
 
            (iv) Also give the coordination number of P and Q. (They form bcc lattice)

Best Answer

Contribution of atoms Q present at 8 corners of the cube
 
             = 1/8*8=1
 
            Contribution of atom P present at the body centre = 1
 
            Therefore, ratio of P and Q = 1: 1 so, the formula is PQ.
 
            Coordination number of atoms P and Q = 8
 
 
 

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