What is Valency?
Valency is defined as the capacity of an atom to give, accept or share electrons to achieve the octet state.
It is the combining capacity of an element. Let us look at some examples to understand this.
- Valency of Hydrogen
Hydrogen has just 1 electron in the outermost shell. Hence, it has to add 1 more electron to the outermost shell. Thus, the valency of hydrogen is 1 as it accepts or shares 1 electron with atoms of other elements.
Valency of hydrogen
- Valency of oxygen
Oxygen has 6 electrons in the outermost shell. As it needs 2 electrons to complete the octet, its valency is 2. It accepts or takes 2 electrons from other atoms for completing the octet.
Valency of oxygen
- Valency of magnesium
Magnesium has 2 electrons in its outermost shell. It needs 6 electrons to complete the octet. In this case, magnesium is more likely to give away 2 electrons from its outermost shell instead of taking 6 electrons and, thus, the valency of magnesium is 2.
Valency of Magnesium
Formation of compounds
The valency of an element decides how many electrons will participate in bond formation and if electrons are given or taken. Let us look at some examples to understand how atoms with different valencies combine with each other to form compounds.
- Sodium chloride
For the formation of one molecule of sodium chloride, we need one atom of sodium and one atom of chlorine. Sodium has the electronic configuration (2,8,1) and chlorine has an electronic configuration (2,8,7).
The valency of both sodium and chlorine is 1. Here, sodium will donate 1 and chlorine will accept 1 electron to complete their respective octet states. This helps in the formation of the sodium chloride molecule.
Formation of sodium chloride
- Water molecule
The valency of hydrogen is 1, while that of oxygen is 2. Here, hydrogen needs 1 electron, while oxygen needs 2 electrons.
Given that both need electrons, they will share electrons with each other. Here, 1 atom of oxygen combines with 2 hydrogen atoms to give 1 water molecule.
Formation of Water