Question #9b3cf

The first thing to do here is to write the electron configuration of a neutral aluminium atom.

Aluminium is located in period 3, group 13 of the Periodic Table of Elements and has a total of #13# electrons surrounding its nucleus, as given by its atomic number.

The electron configuration of a neutral aluminium atom looks like this

#"Al: " 1s^2 2s^2 2p^6 3s^2 color(blue)(3)p^1#

As you can see, the last electron present in an aluminium atom is located in a #3p# orbital.

Now, we need to find the values of the four quantum numbers used to describe the position and spin of an electron inside an atom.

![figures.boundless.com]()

In your case, the principal quantum number, #n#, which gives the energy level on which the electron is located, is equal to #color(blue)(3)#.

The angular momentum quantum number, #l#, which gives you the subshell in which the electron is located, is equal to #1#, since

• #l=0 -># designates the s subshell
• #l=1 -># designates the p subshell
• #l=2 -># designates the d subshell

and so on. The magnetic quantum number, #m_l#, which gives you the orbital which holds the electron, can take one of three possible values here

• #m_l = -1 -># the #3p_x# orbital
• #m_l = color(white)(-)0-># the #3p_z# orbital
• #m_l = color(white)(-)1 -># the #3p_y# orbital

Because in the case of an aluminium atom the p subshell contains a single electron, you can pretty much pick any of these three values for #m_l#.

Let's say that we have #m_l = 0# for an electron located in the #3p_z# orbital.

Finally, the spin quantum number, #m_s#, which tells you the spin of the electron, can be #+1/2# for an electron that has spin-up and #-1/2# for an electron that has spin-down.

Since your electron is alone in the #p_z# orbital, you can pick either value for #m_s#. Let's say that we have #m_s = +1/2#.

Therefore, you can say that a valid set of quantum numbers that describe the last electron added to an aluminium atom could be

#n=3, l=1, m_l = 0, m_s = +1/2#

This describes an electron located on the third energy level, in the 3p-subshell, in the #3p_z# orbital, that has spin-up

You could also have, for example

#n=3, l=1, m_l = -1, m_s = +1/2#

This describes an electron located on the third energy level, in the 3p-subshell, in the #3p_x# orbital, that has spin-up

#n=3, l=1, m_l = 1, m_s = +1/2#

This describes an electron located on the third energy level, in the 3p-subshell, in the #3p_y# orbital, that has spin-up

Here is a video with more explanation of quantum numbers.