Question

What is the electron configuration for `S^(2-)` ion?

Answer 1

`"S"^(2-):1s^2 2s^2 2p^6 3s^2 3p^6`

Explanation:

A good starting point when looking for the electron configuration of an ion is the electron configuration of the neutral atom.

In your case, the neutral atom is sulfur, `"S"`, which is located in period 3, group 16 of the periodic table. Sulfur's has an atomic number equal to `16`, which means that a neutral sulfur atom has a total of `16` electrons surrounding its nucleus.

The electron configuration of a neutral sulfur atom will thus be

`"S: " 1s^2 2s^2 2p^6 3s^2 3p^4`

Now, the sulfide anion, `"S"^(2-)`, is formed when two electrons are added to a neutral sulfur atom.

As you can see in the configuration of the neutral atom, these two electrons will be added to the 3p-orbitals, which can hold a maximum of six electrons between them.

The electron configuration of the sulfide anion will thus be

`"S"^(2-):color(white)(a) 1s^2 2s^2 2p^6 3s^2 3p^6`

The noble gas shorthand notation for the sulfide anion will use the electron configuration of neon, the noble gas that comes immediately before sulfur in the periodic table.

`"S"^(2-): color(white)(a)["Ne"] 3s^2 3p^6`