Two or more @M03986@ are described as isoelectronic if they have the same number of @V06588@ electrons and the same structure, i.e. number and @C01274@ of atoms, but differ in some of the elements involved. Thus: CO, N2 and NO+ are isoelectronic. CH2=C=O and CH2=N=N are isoelectronic. CH3COCH3 and CH3N=NCH3 have the same number of electrons, but have different structures, hence they are not described as isoelectronic.