Arranging the atoms of the third layer directly above those of the first layer creates what type of arrangement_________________?
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Answer: A. ABAB (hexagonal)
Explanation
An ABAB packing arrangement corresponds to a hexagonal close-packed crystal lattice structure. In this sequence, the third layer of atoms is aligned directly above the atoms in the first layer. Alternating layers repeat in a binary pattern to maximize space-filling efficiency in solid metal structures. Close-packing of spheres is a fundamental concept used to describe the microscopic architecture of metallic crystals. Hexagonal close-packing achieves the maximum possible packing efficiency of seventy-four percent for identical spheres. Coordination numbers in hexagonal close-packed structures indicate that each atom is surrounded by twelve nearest neighbors.
Option B refers to a cubic close-packed structure where the repeating sequence follows a three-layer ABCABC pattern. Option C describes a broader crystal system rather than the specific stacking sequence of close-packed atomic layers. Option D represents a crystal system with different symmetry axes rather than this specific alternating atomic layer sequence.
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