Most metals have a crystal structure that is are either body-centered cubic (BCC), face-centered cubic (FCC), or hexagonal close packed (HCP).

The body centered cubic structure consists of one lattice point in the center of the cube in addition to eight corner points.  Many metals such as chromium, iron, tungsten have BCC structure at room temperature.  Visualize it here.

The face centered cubic structure consists of six lattice points at the center of each face of the cube in addition to the eight corner points.  many metals such as aluminum, copper, lead, nickel, and iron crystallize as FCC.  Visualize it here.

The hexagonal close packed structure is similar to the FCC structure, in achieving the highest packing density.  The structures are close packed.    The coordination number or number of closest numbers is maximized (which happens to often minimize the cohesive energy).  Metals such as cadmium, zinc, and titanium have an HCP structure.  Visualize it here.

The simplex hexagonal structure is not close packed.  Visualize the simple hexagonal structure here.  In the simple hexagonal structure, atoms are stacked AAAA.  Atoms are stacked ABAB for hexagonal close packed, and atoms are stacked ABCABC for FCC.

Advertisements