Illustrated Glossary of Organic Chemistry

Isoelectronic: Atoms, ions, or molecules which have an equal number of valence electrons and the same atom connectivity.

Carbon monoxide (CO) and dinitrogen (N₂) are isoelectronic. Both have ten valence electrons.

Ammonia (NH₃) and phosphine (PH₃) are isoelectronic. The nitrogen and phosphorus atoms of these molecules are also isoelectronic.