  LEARNATHON
III

Competition for grade 6 to 10 students! Learn, solve tests and earn prizes!

Theory:

Valency or valence refers to an atom's ability to accept or donate a pair of electrons to form a chemical compound.
The valency of noble gases or inert gases is zero since there are no free electrons in the valence shell, and the elements are already in a stable state.

Example:

The outermost shell of a hydrogen atom contains one electron. One more electron must be added to the outermost shell to achieve a stable state. Since hydrogen accepts only one electron, we decided that its valency is one. It sometimes shares electrons with the element of other atoms.

The oxygen atom has $$8$$ electrons; hence, the electronic configuration is ($$2, 6$$). So, there are six electrons in the outermost shell. Two electrons are needed to complete the octet ($$2, 8$$). Thus, the valency of oxygen is $$2$$.

Similarly, the magnesium atom has $$12$$ electrons, hence, the electronic configuration of magnesium is ($$2, 8, 2$$). There are two valence electrons in the outermost shell. For achieving the octet, it requires $$6$$ electrons. It is impossible for an atom to give $$6$$ electrons.  Electron distribution in $$O$$ and $$Mg$$

Then, how can Magnesium complete its octet?

We already know that an atom can lose electrons to achieve the octet. So, it is easy to donate $$2$$ electrons to other atoms to achieve the octet. Hence, the valency of magnesium is $$2$$.
Formation of a bond or compound or molecule
Lets us consider the formation of $$NaCl$$ molecule. We need one $$Na$$ atom and one $$Cl$$ atom to form the compound $$NaCl$$.

 Sodium atom Chlorine atom Electrons present = $$11$$Electronic configuration = ($$2, 8, 1$$) Electrons present = $$17$$Electronic configuration = ($$2, 8, 7$$) Where sodium will donate $$1$$ electron to the chlorine atom to complete their respective octets; in this way, the molecule sodium chloride ($$NaCl$$) will form. Formation of sodium chloride molecule