Question

What is the valency of Magnesium with atomic number 12?
A.2
B.4
C.6
D.5

Answer 1

Hint: To find the valency of magnesium, we must know the atomic number of it because it tells us the number of electrons of the atom. Knowing the group in which the atom is located makes it easier to know the valency directly.

Complete answer:
-Valency is the number of the electrons present in the outermost shell of an atom which is also called the valence shell of an atom. Those electrons are important to be studied as they are the most loosely held electrons of the atoms.
-Magnesium is an atom with the atomic number 12. It comes right after sodium Na.
-If we have a look at the periodic table, we can find that Magnesium is present in group 2 A of the periodic table.
-As the atomic number of magnesium is 12, the number of electrons in Magnesium is also 12 since we know,
 Atomic no. = No. of proton = No. of electron
-Now according to Hund’s rule, the 12 electrons of Magnesium are filled in their orbitals as $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}$
-Thus, we see that there are 2 electrons in the 1st orbital, 8 electrons in the 2nd orbital and 2 electrons in the last orbital of Magnesium.
So the electronic configuration of Magnesium is (2,8,2).
-Now, we know that every atom tries to reach the electronic configuration of the noble gases to become stable like them. The configuration of noble gases is of the form $n{{s}^{2}}n{{p}^{6}}$ .
-This configuration is reached either by sharing of electrons or losing of electrons.
-Magnesium loses 2 electrons of the outermost 3s shell to achieve the configuration of its nearest noble gas-Neon.
-We all know that the valency is the number of outermost electrons of the atom. It states the combining capacity of the atom.
Therefore, the valency of Magnesium is 2.

The correct option is A.

Note:
Valency is not always told by the number of outermost electrons. This holds only when the number of outermost electrons are in between 1 to 4. If the outermost electrons are more than 4, then the valency is found by subtracting those electrons from 8.
Eg, if the outermost electrons are 6, then the valency is 8-6=2, not 6.
If the outermost electrons are 7, then the valency is 8-7=1, not 7.