|
Isoelectronicity Carbon monoxide molecule  Nitrosonium ion Carbon monoxide and nitrosonium are isoelectronic 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. For example, CO, NO+ This definition is sometimes termed valence isoelectronicity. Definitions can sometimes be not as strict, sometimes requiring identity of the total electron count and with it the entire electronic configuration.[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. In quantum mechanics, hydrogen-like atoms are ions with only one electron such as Li2+ ExamplesThree isoelectronic amino acids  Dimethyl ether -Azomethane.svg) Azomethane Both molecules have the same electron configuration, but due to the double bond and extra atom in azomethane, they are not isoelectronic The N atom and the O+ Similarly, the cations K+ CO, CN− Molecular orbital diagrams best illustrate isoelectronicity in diatomic molecules, showing how atomic orbital mixing in isoelectronic species results in identical orbital combination, and thus also bonding. More complex molecules can be polyatomic also. For example, the amino acids serine, cysteine, and selenocysteine are all isoelectronic to each other. They differ by which specific chalcogen is present at one location in the side-chain. CH See alsoReferences
|
