Question

How do you determine if and ion has a noble-gasconfiguration?

Answer 1

Explanation:

Noble gas configuration is defined as the configuration which contains completely filled orbitals.

For example, oxygen atom when gain two electrons then it forms oxygen ion ($O^{2-}$).

Atomic number of oxygen atom is 8 and so, its number of electrons will also be 8. But when it gain two electrons then it has total 10 electrons. Hence, electronic configuration of $O^{2-}$ is as follows.

          $1s^{2}2s^{2}2p^{6}$

Since, there are completely filled orbitals in an $O^{2-}$ ions. Therefore, it means this ion has a  noble-gas configuration.

Thus, we can conclude that any specie which shows completely filled orbitals will have noble-gas configuration.