Even though the size of the atoms and the interatomic distances in the two arrays are the same, the arrays differ in how efficiently they are packed because the number of nearest neighbors about the atoms in each array is different.

The number of neighbors nearest to an atom is called the atom's coordination number. The atoms that are closest to an atom are called the atom's coordination sphere.

Use the links on the right to either show or hide the interatomic distances in the two arrays.