Question

What element has the electron configuration of `3s^2 3p^4` in its outermost shell?

Answer 1

Sulfur.

Explanation:

The first thing to note here is that for a given element, the energy level on which the outermost electrons reside gives you the period in which the element is located in the periodic table.

In this case, your element is said to have the electron configuration

`color(red)(3)s^2 color(red)(3)p^4`

in its outermost shell, which implies that this element is located in period `color(red)(3)` of the periodic table.

Now, the great thing about elements located in period 3 is that they are all main-group elements, i.e. they are located in group 1, 2, or 13 through 18.

Consequently, the total number of electrons located in the outermost shell gives you the group in which the element is located in the periodic table.

In this case, the outermost shell contains

• `"2 e"^(-) ->` located in the 3s orbital

• `"4 e"^(-) ->` located in the 3p orbitals

The total number of electrons located in this shell is

`"2 e"^(-) + "4 e"^(-) = color(blue)("6 e"^(-))`

which means that the element is located in group `1color(blue)(6)`. A quick look in the periodic table will reveal that your unknown element is sulfur, `"S"`, which has the complete electron configuration

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