Isoelectronicity

Two or more molecular entities (atoms, molecules, ions) are described as being isoelectronic [GoldBookRef | file = I03276 | title = isoelectronic] with each other if they have the same number of valence electrons "and" the same structure (number and connectivity of atoms), regardless of the nature of the elements involved.

Examples

The N atom and the O⁺ radical ion are isoelectronic because each has 5 electrons in the outer electronic shell. Similarly, the cations K⁺, Ca²⁺, and Sc³⁺, the anions Cl⁻, S²⁻, and P³⁻ are all isolectronic with the Ar atom. In such monatomic cases, there is a clear trend in the sizes of such species, with atomic radius decreasing as charge increases.

CO, N₂ and NO⁺ are isoelectronic because each have 2 nuclei and 10 valence electrons (4+6, 5+5, and 5+5, respectively).

The uncharged H₂C=C=O molecule and the zwitterionic CH₂=N⁺=N^- molecule are isoelectronic.

CH₃COCH₃ and CH₃N₂CH₃ 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 (CH₃) groups attached to carbonyl's (CO's) carbon atom, forming a trigonal planar structure: H₃C-C(=O)-CH₃; the second molecule's structure is linear: H₃C-N=N-CH₃ and its methyl groups are not connected to the same nitrogen atom.

The amino acids cysteine and serine are also considered isoelectronic.

References

ee also

*Atom
*Molecule
*Ion
*Electron
*Electronic configuration
*Valence bond theory