Question

How many valence electrons are in an atom of magnesium?

Answer 1

Hint The valence electrons are those present in the outermost shell which is actively involved in the chemical reactions. The atomic number of magnesium is 12 and is placed with group -2 elements.

Complete answer:
> From the time we are studying about the periodic table and the elements, we are concerned about the arrangement of electrons in atoms, the total number of electrons present in them and the number of valence electrons present. So that we will get an idea of the various oxidation states that an element can possess and various types of chemical reaction an element can undergo.
> So, the arrangement of electrons in an atom is of great concern and especially the number of valence electrons and various shells present in the atom has great effect in various properties shown by the element.
- Now let’s see what valence electrons mean and what their significance is.
> So, we are very familiar with the term valence shell or valence orbit; it is the outermost shell present in the atom. Hence we can say that the valence electrons is the electrons present in the outermost shell of the electrons and these electrons are removed to obtain the octet configuration or in some atoms electrons are accepted by the atoms which enters the valence shell to get the stable noble gas configuration i.e. the octet configuration.
> Now, let’s find the atomic number of Mg from which we will get the number of electrons. By knowing the number of electrons we can distribute it in various shells by which we can find the total valence electrons in the last shell.
> The total number of electrons present in Mg is 12, since the atomic number of Mg is 12. Now we have to distribute the electrons in various orbitals present in the shells.
Electronic configuration of Mg is, $1s^{2}2s^{2}2p^{6}3s^2$
> So, the outermost shell present in Mg is the third shell, which has two electrons in them.

So, the total number of valence electrons present in the Mg atom is 2.

Note: Magnesium possesses a valency of +2, since there are two valence electrons present in Mg which on removal yields the stable noble gas configuration of Ne. Hence Mg also tends to lose 2 electrons and obtain the stable configuration. We can also comment on the valency electrons of an element if the main group number of the given element is known. Since Mg belongs to group 2, the valence electrons will be two as the common valency of the alkaline earth group is 2.