Think of a stacked pyramid of grapefruit in a supermarket. Each grapefruit fits closely in a repeating pattern, leaving gaps, or interstices, between itself and the other grapefruit. The atoms of metallic elements form very similar repeating, crystalline patterns. Scientists categorize these repeating structures of identical arrangements of atoms within them as "unit cells." There are three types of unit cells: primitive, body-centered and face-centered. You'll have no trouble calculating the number of atoms represented by each type of cubic unit cell.
Instructions
Multiply the number of corner atoms by 1/8. There are eight
corner atoms in a simple cubic structure: 8 x 1/8 = 1. There is one
atom per primitive, or simple, cubic structure.
Multiply the number of corner atoms by 1/8 and add one for
an atom in the center of the cell. There are eight corner atoms and
one atom in the center of a body-centered cubic structure: (8 x
1/8) + 1 = 2. There are two atoms per body-centered cubic
structure.
Multiply the number of corner atoms by 1/8 and the number of
face atoms by 1/2. There are eight corner atoms and six face atoms
in a face-centered cubic structure: (8 x 1/8) + (6 x 1/2) = 4.
There are four atoms per face-centered cubic structure.
|
