CHEM 121 glossary

Isoelectronic

Having the same number of electrons (and so the same configuration). Count electrons as $Z$ minus the charge; isoelectronic ions differ only in nuclear charge, so the one with more protons is smaller.

The 10-electron configuration shared by $\ce{N^3-}$ , $\ce{O^2-}$ , $\ce{F-}$ , $\ce{Ne}$ , $\ce{Na+}$ , $\ce{Mg^2+}$ and $\ce{Al^3+}$ .

Example

The idea works for molecules too: $\ce{N2}$ , $\ce{CO}$ and $\ce{CN-}$ all have 14 electrons, and all three have a triple bond.