<P> CO, FCN, N O, NO, N, NCO, and CN are all isoelectronic, and each has multiple resonance forms: one with two double bonds and 2 lone pairs on each of the outer atoms, and one with one single bond and one triple bond . </P> <P> Isoelectronicity leads to the concept of hydrogen - like atoms, ions with one electron which are thus isoelectronic with hydrogen . </P> <P> The uncharged H C = C =O (ethenone) and H N - C ≡ N (cyanamide) molecules and the zwitterionic H C = N = N (diazomethane) molecule are isoelectronic . </P> <P> CH COCH (acetone) and CH CH (dimethyl diazene) are not isoelectronic . They do have the same number of nuclei and the same number of valence electrons, but the atoms' connectivity is different: the first one has both methyl (CH) groups attached to carbonyl's (CO's) carbon atom, forming a branched trigonal planar shape: H C-C (= O) - CH; the second molecule's structure has a consecutive attachment of the main atoms: H C-N = N - CH and its methyl groups are not connected to the same nitrogen atom . </P>

H3o+ and nh3 are considered isoelectronic. why