Question

The valency of chlorine atom is________and this value is taken as the standard value.

Answer 1

Write the electronic configuration of the chlorine atom and see how many elements are there in its valence shell. Chlorine is a non-metal. In nonmetals the number of electrons required to complete an octet will be its valency.

Complete step by step answer:
In simple terms, valency means the combining capacity of any element. In finding the valency of an element , the two important things are its atomic number and its electronic configuration . Atomic number of elements is actually the number of protons present in it.
The atomic number of chlorine is $17$ and its electronic configuration is $2,8,7$ ( This is actually the number of electrons in $K,L,M$ shell respectively.
The easiest way for chlorine to gain noble gas configuration i.e. $2,8,8$ and become stable will be the gain of an electron from any other atom. The chlorine element belongs to group $17$ because it has $7$ valence electron . Its valency is $1$ . It can gain one electron from any other atom to become stable. This means that it can never form a double or triple bond.
Hence , we conclude that the valency of chlorine is $1$ .

Note: Chlorine belongs to the p-block of the periodic table. It is non-metal. For p-block elements the valency of an element is given by - $18 -$(group number of the element) . It will always form a single bond with any atom.