Sodium has body - centered packing. The distance between two nearest atoms is 3.7A^o .
Corrosionpedia Explains Body-Centered Cubic (BCC)
The atoms do not touch along the edges of the cube. Instead, the atoms touch along the cube's diagonal. In other words, the central atom touches all of the corner atoms. One of the other parameters used to define the BCC structure is packing density.
A third common packing arrangement in metals, the body-centered cubic (BCC) unit cell has atoms at each of the eight corners of a cube plus one atom in the center of the cube. Because each of the corner atoms is the corner of another cube, the corner atoms in each unit cell will be shared among eight unit cells.
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