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 =8×18 = 1. 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.  Text Solution Solution : If n atoms of Y are involved in the formation of ccp structure, then number of tetrahedral voids in the Structure is 2n . Of the 2n tetrahedral voids, 1/3rd is occupied by X atoms. So, number of X atoms in the structure is `(2n)/3`. <br> Thus, the ratio of X and Y atom is `(2n)/2:n=2:3`. Hence, the formula of the compound will be `X_(2)Y_(3)`. |
What is the formula of a compound in which the element forms CCP lattice and atoms of Occupy of octahedral voids?
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