Answer
The electron configuration for $S^{2-}$ is $$S^{2-}: [Ne]3s^23p^6$$
$S^{2-}$ has the configuration of noble gas $Ar$.
Work Step by Step
*RULES TO WRITE ELECTRON CONFIGURATIONS FOR IONS:
- When electrons are removed to form cations, those of the orbitals that have the largest principal quantum number $n$ will be removed first.
- If there are more than one subshell for a given $n$, electrons of the subshell with the highest value of $l$ will be removed first.
- When electrons are added to form anions, they would be added to the empty or partially occupied subshell with the lowest value of $n$.
1) The electron configuration of a neutral $S$ atom is $$S: [Ne]3s^23p^4$$
2) Here we need to find the electron configuration for $S^{2-}$, an ion having 2 electrons added to a neutral $S$ atom.
Therefore, according to the rules, when electrons are added, we would look for the empty or partially occupied subshell with the lowest $n$.
All the inner orbitals are fully occupied, so we don't care about them. Subshell $3s$ is already occupied by 2 electrons, so it is also fully occupied.
Subshell $3p$, on the other hand, is occupied by only 4 electrons, while its maximum capacity is 6 electrons. So, electrons would be added to here first.
3) 2 electrons need to be added to a neutral $S$ atom to make $S^{2-}$. Subshell $3p$ also have 2 spots left for 2 electrons, so these 2 electrons would be added here.
That means the electron configuration for $S^{2-}$ is $$S^{2-}: [Ne]3s^23p^6$$
The above configuration is the configuration of noble gas $Ar$, so $S^{2-}$ has the configuration of noble gas $Ar$.