The top and bottom layers contain six atoms at the corners of a hexagon and one atom at the center of each hexagon. In a hexagonal close-packed (HCP) arrangement of atoms, the unit cell consists of three layers of atoms. These metals possess low strength and high ductility. Metals containing FCC structures include austenite, aluminum, copper, lead, silver, gold, nickel, platinum, and thorium. This structure, along with its hexagonal relative (hcp), has the most efficient packing (74%). In a face-centered cubic arrangement, a unit cell contains (8 corner atoms × ⅛) + (6 face atoms × ½) = 4 atoms. Face-centered Cubic.In a face-centered cubic (FCC) arrangement of atoms, the unit cell consists of eight atoms at the corners of a cube and one atom at the center of each of the faces of the cube.These metals possess high strength and low ductility.
Metals containing BCC structures include ferrite, chromium, vanadium, molybdenum, and tungsten. The packing is more efficient (68%) than simple cubic and the structure is a common one for alkali metals and early transition metals. In a body-centered cubic arrangement, a unit cell contains (8 corner atoms × ⅛) + (1 center atom × 1) = 2 atoms. In a body-centered cubic (BCC) arrangement of atoms, the unit cell consists of eight atoms at the corners of a cube and one atom at the body center of the cube. The three most common basic crystal patterns are: There are 14 general types of such patterns known as Bravais lattices. It is this repeated pattern which control properties like strength, ductility, density, conductivity (property of conducting or transmitting heat, electricity, etc.), and shape.
The forces of chemical bonding causes this repetition. A crystal lattice is a repeating pattern of mathematical points that extends throughout space.
In metals, and in many other solids, the atoms are arranged in regular arrays called crystals. A possible crystal structure of Antimony is rhombohedral structure.
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