Crystal has face centred cubic structure, having atomic weight 6.023y g mol^-1. If the minimum distance between two atoms is y^(1//3) nm and the observed density is 20 kg m^-3 find type of defect in crystal lattice.

Crystal has face centred cubic structure, having atomic weight 6.023y

1.	Crystal has face centred cubic structure, having atomic weight 6.023y g mol^-1. If the minimum distance between two atoms is y^(1//3) nm and the observed density is 20 kg m^-3 find type of defect in crystal lattice.
Answer» Solution :AB has a rock salt (NaCl) structure. This TYPE of crystal structure possesses fcc unit cell and contains four formula units PER unit cell, i.e., Z = 4. In CASE of a rock salt structure, the edge length (a) of the unit cell = 2 `xx` (radius of cation + radius of anion) Therefore, the edge length (a) of the unit cell of AB crystal = `2xxY^(1//3)nm=2Y^(1//3)xx10^(-9)m`. We know, `rho=(ZxxM)/(Nxxa^(3))` GIVEN: `M=6.022Ygmol^(-1)=6.022xx10^(-3)Ykgmol^(-1)` `therefore" "rho=(4xx6.022xx10^(-3)Y)/(6.022xx10^(23)xx(2Y^(1//3)xx10^(-9))^(3))=5.0kgm^(-3)` (1) Density of the crystal = `5.0kgm^(-3)` (2) The observed density `(=20kg*m^(-3))` is higher than that of the calculated density. This indicates that the crystal structure of AB is likely to have non-stoichiometric defect in the form of metal excess or metal deficiency defect or to have impurity defect in the form of substitutional impurity defect or interstitial impurity defect.