Isoelectronicity is a

phenomenon A phenomenon ( phenomena), sometimes spelled phaenomenon, is an observable Event (philosophy), event. The term came into its modern Philosophy, philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be ...

observed when two or more

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s have the same

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

(positions and connectivities among

atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

s) and the same electronic configurations, but differ by what specific elements are at certain locations in the structure. For example, , , and are isoelectronic, while and = are not. This definition is sometimes termed valence isoelectronicity. Definitions can sometimes be not as strict, sometimes requiring identity of the total

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

count and with it the entire electronic configuration. More usually, definitions are broader, and may extend to allowing different numbers of atoms in the

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

being compared.A. A. Aradi & T. P. Fehlner, "Isoelectronic Organometallic Molecules", in F. G. A. Stone & Robert West (eds.) ''Advances in Organometallic Chemistry Vol. 30'' (1990), Chapter 5 (at p. 190
google books link
/ref> 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 Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...

of the atoms in isolelectronic species can affect reactivity. In

quantum mechanics Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Addison-Wesley, 1989, It is ...

, hydrogen-like atoms are ions with only one electron such as . These ions would be described as being isoelectronic with

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

Examples

The atom and the ion are isoelectronic because each has five valence electrons, or more accurately an electronic configuration of e2s² 2p³. Similarly, the

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s , , and and the

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s , , and are all isoelectronic with the atom. , , , and are isoelectronic because each has two atoms triple bonded together, and due to the charge have analogous electronic configurations ( is identical in electronic configuration to so is identical electronically to ). Molecular orbital diagrams best illustrate isoelectronicity in diatomic molecules, showing how

atomic orbital In quantum mechanics, an atomic orbital () is a Function (mathematics), function describing the location and Matter wave, wave-like behavior of an electron in an atom. This function describes an electron's Charge density, charge distribution a ...

mixing in isoelectronic species results in identical orbital combination, and thus also bonding. More complex molecules can be polyatomic also. For example, the

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s serine,

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

, and selenocysteine are all isoelectronic to each other. They differ by which specific

chalcogen The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the rad ...

is present at one location in the side-chain. (

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

) and ( azomethane) are not isoelectronic. They do have the same number of electrons but they do not have the same structure.

References

{{Reflist Theoretical chemistry

Examples

See also

References