Question

What is meant by valency of elements?

Answer 1

Hint: Valency determines the number of unpaired electrons present in the outermost shell of an atom of any element. It tells us about the combining capacity of an atom with another atom. So, valency of an element depicts the ability of an element to combine with other elements.

Complete answer:
The property of an element which tells about its power of combining with other elements is known as valency. It is a measure of no. of electrons present in the outermost shell of an atom. For example- the electronic configuration of oxygen is $1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^4$, there are 6 electrons present in the outermost shell but s-subshell is filled completely as it contains 2 electrons and p-subshell can contain maximum of 6 electrons and out of 4 electrons present in p-subshell, 2 are unpaired so valency of oxygen is 2 i.e. its combining capacity is 2.
Some elements can have more than one valency. There is no positive or negative valency; valency does not have any sign. The origin of valency is from Greek word ‘valentia’ meaning strength and capacity. This concept was developed to understand the molecular structure of organic and inorganic compounds.

Note:
There can be confusion between valency and oxidation number. Oxidation number determines the total no. of electrons gained or lost by an atom to form chemical bonds with other atoms. Oxidation number can be positive or negative depending on the electrons lost or gained by an atom respectively while valency do not have any positive or negative sign.