Metallic bond

In 3D

Metal aromaticity in metal clusters is another example of delocalization, this time often in three-dimensional arrangements. Metals take the delocalization principle to its extreme, and one could say that a crystal of a metal represents a single molecule over which all conduction electrons are delocalized in all three dimensions. This means that inside the metal, one can generally not distinguish molecules, so that the metallic bonding is neither intra- nor inter-molecular. Metallic bonding is mostly non-polar, because there is little to no difference, even in alloys, among the electronegativities of the atoms participating in the bonding interaction. Thus, metallic bonding is an extremely delocalized communal form of covalent bonding. Metallic bonding may be described as not a unique type of bond at all, as it describes the bonding only as present in a portion of condensed matter, be it crystalline solid or liquid. Metallic vapors, in contrast, are often atomic (Hg) or at times contain molecules, such as Na₂, held together by a more conventional covalent bond. This is why it is not correct to speak of a single 'metallic bond'.