Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in the structure.
[2] More usually, definitions are broader, and may extend to allowing different numbers of atoms in the species being compared.
[3] The importance of the concept lies in identifying significantly related species, as pairs or series.
Isoelectronic species can be expected to show useful consistency and predictability in their properties, so identifying a compound as isoelectronic with one already characterised offers clues to possible properties and reactions.
Differences in properties such as electronegativity of the atoms in isolelectronic species can affect reactivity.