Superatoms are clusters of atoms which seem to exhibit some of the properties of elemental atoms.

Sodium atoms when left to condense in clusters from vapour naturally form into clusters of 8, 20, 40, 58 or 92 atoms. The first of these can be recognised as the number of electrons in filled s and p orbitals. The suggestion is that free electrons in the cluster form atomic like structure (larger numbers show deviations from the number of electrons in a shell as the potential is not central).

Clusters of 13 aluminium atoms with an extra electron added appear not to react with oxygen. Assuming each atom liberates its 3 valence electrons, this means that there are 40 elctrons present, which is one of the magic numbers noted for sodium, and implies that these numbers are a reflection of the nobel gases .

Similaly it has been noted that clusters with one greater or fewer than the magic numbers appear to exhibit the properties of a alkali metal or halogen.

References

Philip Ball, "A New Kind of Alchemy", New Scientist Issue dated 2005-04-16 .