Valency
The outermost electron shell of an atom is called the valence shell. The electrons present in the outermost shell of an atom are called valence electrons. The valence electron of an atom takes part in a chemical reaction because they have more energy than all the inner electrons.
The combining capacity of an atom of an element to form a chemical bond is called its valency.
The valency of an element is
(1) Equal to the number of valence electrons
(2) Equal to the number of electrons required to complete eight electrons in a valence shell.
Valency of a metal=No. of Valence electrons
Valency of a non-metal=8-No. of valence electrons
For Example :
(1) Sodium (Z=11)
Electronic Configuration=2,8,1
Valency=1
(2) Oxygen (Z=16)
Electronic Configuration=2,8,6
Valency=8-6=2
There are some elements which do not combine with other elements. They are known as noble gases or inert gases.
For Example:
Helium (Z=2)
Electronic Configuration=2
Valency=2