3.1 What is the difference between crystal structure and crystal system?
A crystal structure is described by both the geometry and atomic arrangements within cell, whereas a crystal system is described only in terms of the cell geometry.
3.2 For cubic crystals, as values of the planar indices h, k, and l increase, does the distance between adjacent and parallel planes (i.e., the interplanar spacing) increase or decrease? Why?
The interplanar spacing between adjacent and parallel planes decreases as the values of h, k, and l increase. As values of the planar indices increase, the magnitude of the denominator in increases, with the result that the interplanar spacing (dhkl) decreases.
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