two or more molecular entities are described as isoelectronic if they have the same number of valence electrons and the same structure, i.e. number and connectivity of atoms, but differ in some of the elements involved, kaks või enam molekulaarset osakest on isoelektronilised, kui neil on ühesugune arv valentselektrone ja ühesugune struktuur, ehkki nad erinevad elementkoostiselt