4. Compare and contrast SC, BCC, FCC and HCP in terms of coordination number, number of atoms per unit cell and packing fraction.

What are unit cell? What is the atomic packing factor? What are the atomic packing factors of BCC, FCC and HCP? Does the volume increase or decrease when FCC iron changes to BCC iron? Why?

3.Which of the following is not true about the basic building block of silicate minerals?     (2 نقطة) The atoms of the basic tetrahedron are strong ionically bonded together It can share oxygen atoms and be linked in a variety of ways, which results in different structures It contains one silicon atom and four oxygen atoms, each at the corner of a regular tetrahedron The negative charge of each silicate is balanced by two divalent cations The common ions in silicate have a wide range of sizes

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