Answer:
The correct noble gas configuration for magnesium is [Ne] 3s2
Explanation:
Every element of the Periodic Table has a diferent electronic configuration, but all the elements located in the same period of the table has the same "noble gas configuration" in which there are the internal electrons to which they must be added the valence electrons.
The atomic number (indicates the amount of electrons of the atom, that are equal to protons number) of magnesium is 12 so, we have to look at the noble gas of the previuos period of magnesium wich is Neon.
The electronic configuration of Neon is:
1 s 2
2 s 2
2 p 6
That's why Neon has 10 electrons (it's atomic number).
As magnesium has 12 electrons, it is necesary to add 2 electrons more in their noble gas confogutation. That's why the electronic configuration of magnesium is:
1 s 2
2 s 2
2 p 6
3 s 2
In order to make the electronic configuration more simple we write it making reference to the previuos noble gas of the element we are analizing.
Also the period number of each atom tell us wich is the latest shell where the valence electrons are located. So, the period of magnesium is 3, that means that magnesium has its valence electrons at level number 3, excatly the same latest number of its electronic configuration.
Morover, the group number of an element indicates the amount of electrons it has in the latest shell (called "valence shell"). In the case of magnesium, it is at group number 2 so it has 2 electrons located in the latest level.
In this way, you can complete the electronic configuration looking at the previuos noble gas and the period and group number of an element.
