Valency is known as the capacity of an atom or a molecule to combine.
To calculate valency of an atom or a molecule we consider the electrons present in the valence shell, i.e. outermost shell.
Valency of nitrate:-
(Nitrate ion) has three oxygen atoms and one nitrogen atom.
Structure of nitrate ion
Nitrogen belongs to group -15 in the periodic table, forms bonds with three oxygen atoms.
Since Nitrogen can form only 3 bonds, the formation of 4 bonds leads to a positive charge of +1.
Oxygen belongs to the group – 16 in the periodic table, thus, it has a valency (-2), and forms 2 bonds.
From the structure, it is clear that the positive charge on nitrogen atom is balanced by the negative charge on 1 oxygen atom, and 1 extra charge is left. Therefore Nitrate ion have 1 charge or valency.
