a) What are the differences between crystalline materials and amorphous materials? Briefly explain why covalently bonded

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a) What are the differences between crystalline materials and
amorphous materials? Briefly explain why covalently bonded
materials are generally less dense than ionically or metallically
bonded ones. (8 marks)
(b) Copper has an atomic radius of 0.128 nm, face centered cubic
(FCC) crystal structure with molar mass of 63.5 g mol-1 . (i)
Calculate the density of copper. (ii) Determine the linear density
and packing fraction for FCC copper in the [101] and [110]
directions. (iii) Determine the planar density and packing fraction
for FCC copper in the (101) and (110) planes. (12 marks)
(c) What is meant by crystallographic direction and
crystallographic plane? Within the cubic unit cell, sketch the
following directions and planes: (i) Directions of [ -1 1 2] and [1
-2 0]. (ii) Planes of ( -1 0 3) and (1 -1 4).