Isoelectronicity

Two or more molecular entities (atoms, molecules, ions) are described as being isoelectronic^[1] 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.

Additional recommended knowledge

Daily Visual Balance Check

What is the Correct Way to Check Repeatability in Balances?

Safe Weighing Range Ensures Accurate Results

Examples

N and the O⁺ ion are isoelectronic because each has 5 electrons in the outer electronic shell.

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

CH₂=C=O and CH₂=N⁺=N^- 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; the second molecule's structure is linear: H₃C-N=N-CH₃; methyl groups are not connected to the same nitrogen atom.

Notes

1. ^ Compendium of Chemical Terminology, isoelectronic

See also

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