Isoelectronicity

Isoelectronicity is a property of chemical species, which includes atoms, molecules, and ions. Two molecular entities are isoelectronic if they have the same number of valence electrons and the same structure of chemical bonds, even if the chemical elements involved are different.^[1]

The word isoelectronic comes from the prefix iso-, meaning "same".

Examples

Chemical elements that share a group in the periodic table are isoelectronic. Metallic beryllium, magnesium, calcium, and strontium all have two valence electrons.

Many main group elements form ions that are isoelectronic to noble gases. The sodium cation Na⁺ and fluorine anion F⁻ are both isoelectronic to neon.

Carbon monoxide C≡O and nitrogen N≡N are isoelectronic because each atom has a lone pair and a triple bond. They are also isoelectronic to the nitrosonium cation [N≡O]⁺ and cyanide anion [C≡N]⁻.^[1][source?]

Ethenone CH₂=C=O is isoelectronic with CH₂=N=N, a tautomer of diazomethane.^[1] Diazomethane's other tautomer, CH₂−N≡N, is isoelectronic with cyanamide, NH₂−C≡N.^[source?]

Acetone CH₃COCH₃ and azomethane CH₃N=NCH₃ are not isoelectronic. Although they have the same number of valence electrons, the structure of their chemical bonds is different.^[1]