Structure of Some Ionic Compounds



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Relation between nearest neighbour distance and radius of atom, Concept of Radius ratio

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Relationship between the nearest neighbour distance (d), edge of the unit cell (a) and the radius of the atom (r) (1)Simple cubic unit cell- Distance between nearest neighbour (d) = AB = a Hence for simple cubic (SC)  d = a   and r = a/2 (2)Face centred cubic unit cell-    Distance between nearest neighbour (d) =  AC (Because spheres at the face diagonal are touching each other)    But from  ∆ ABC      AC2 = AB2 + BC2                       Hence        d = a2 + a2                                  d =  2a2                             d =  √2a                             d =a/ √2...
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Crystal System & Bravais Lattices

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Crystal system and Bravais lattices -   Crystal system and Bravais lattices - Based upon the dimensions of the unit cells (i.e. length a, b, and c and the angles (α , β and γ ) there are seven types of unit cells. These are also called crystal systems are crystal habits because any crystalline solid must belong to any one of the unit cells. “At first sight there seems to be infinite number of shapes of crystals. However careful examination of several thousand crystals of various substances has revealed that only seven possible symmetries are possible. The seven different combinations of symmetry elements are called crystal systems.”  These crystal systems differ in the length of the unit cell edges (a, b and c) and angles ( α, β and γ ) between the unit cell The arrangement of particles in the study of crystal was first given by German Scientist M. Frankenheim in 1844. Classification on the basis of geometrical consideration-  In 1848 A. Br...
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Tertahadral & Octahedral Voids, HCP & CCP

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Concepts of Voids, HCP & CCP Arrangements Density of unit cell- Tetrahedral and Octahedral void-  Tetrahedral Void-                                                                              A simple triangular void in a crystal which is surrounded by four spheres is called tetrahedral void. A tetrahedral void is developed when triangular voids have contact with one sphere either in the upper layer or in the lower layer. Tetrahedral void means the tetrahedral arrangement of spheres.                                            .     Characteristics of tetrahedral void- (i) Ratio of radii of void and constituent part...
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