Isoelectronic Definition

What Does Isoelectronic Mean in Chemistry?

Isoelectronic chemical species have the same number of valence electrons.
Isoelectronic chemical species have the same number of valence electrons. Science Photo Library - MEHAU KULYK, Getty Images

Isoelectronic Definition

Isoelectronic refers to two atoms, ions or molecules that have the same electronic structure and same number of valence electrons. The term means "equal electric" or "equal charge". Isoelectronic chemical species typically display similar chemical properties. Atoms or ions with the same electronic configurations are said to be isoelectronic to each other or to have the same isoelectronicity.

Related Terms: Isoelectronicity, Valence-Isoelectronic

Isoelectronic Examples

The K+ ion is isoelectronic with the Ca2+ ion. The carbon monoxide molecule (CO) is isoelectronic to nitrogen gas (N2) and NO+. CH2=C=O is isoelectronic to CH2=N=N.

CH3COCH3 and CH3N=NCH3 are not isoelectronic. They have the same number of electrons, but different electron structures.

The amino acids cysteine, serine, tellurocysteine, and selenocysteine are isoelectronic, at least with respect to valence electrons.

More Examples of Isoelectronic Ions and Elements

Isoelectronic Ions/ElementsElectron Configuration
He, Li+1s2
He, Be2+1s2
Ne, F-1s2 2s2 2p6
Na+, Mg2+1s2 2s2 2p6
K, Ca2+[Ne]4s1
Ar, S2-1s2 2s2 2p6 3s2 3p6 
S2-, P3-1s2 2s2 2p6 3s2 3p6 

Uses of Isoelectronicity

Isoelectronicity may be used to predict the properties and reactions of a species. It is used to identify hydrogen-like atoms, which have one valence electron and are thus isoelectronic to hydrogen.

The concept may be applied to predict or identify unknown or rare compounds based on their electronic resemblance to known species.

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Helmenstine, Anne Marie, Ph.D. "Isoelectronic Definition." ThoughtCo, May. 17, 2017, Helmenstine, Anne Marie, Ph.D. (2017, May 17). Isoelectronic Definition. Retrieved from Helmenstine, Anne Marie, Ph.D. "Isoelectronic Definition." ThoughtCo. (accessed March 21, 2018).