Question

What is meant by valency of an element? What is the relationship between the number of valence electron and valency?

Answer 1

Valency of an element : It is the combining power of an atom of the element.
Valency of an atom is determined by its electronic configuration.
It gives idea about the number of electrons loss or gain in order to achieve the nearest noble gas configuration .

Relationship between valency and valence electron:
a. When the number of valence electrons is 4 or less than 4; valency of element is equal to that of number of valence electron.
b. When the number of valence electrons is more than 4 (upto 8); valency is equal to 8 minus the number of valence electrons.

For example: Na(11) = 2,8,1 So, its valency is1
Cl(17) = 2,8,7 So, its valency is (8-7) = 1