Question

Calculate the formal charge on all the atoms present in the $N{{O}_{3}}^{-}$ion.

Answer 1

Hint: As we know that formal charge of an atom in a polyatomic molecule or ion is usually the difference between the valence electrons of that atom in its elemental state and the number of electrons assigned to that atom in Lewis structure of that molecule or ion. So here we have to calculate the same for all atoms in $N{{O}_{3}}^{-}$ ion.

Complete answer:
Let us first discuss the concept of formal charge as follows:-
-Formal charge: It is also known as Fake charge and it is generally the difference between the valence electrons of an atom in its elemental state and the number of electrons assigned to that atom in the Lewis structure of a molecule or ion. In order to calculate the formal charge of an atom in a given molecule or ion, draw its Lewis structure so as to count the bonding and non-bonding electrons available. It is calculated as follows:-
Formal charge = [Total no. of valence electrons in Free State] – [Total no. of electrons assigned in Lewis structure]
Formal charge = [Total no. of valence electrons in Free State] – [Total no. of non-bonding pair electrons (or lone pair)] – 1/2 [Total no. of bonding electrons]
-The Lewis structure of $N{{O}_{3}}^{-}$ ion is shown below:-
-Formal charge on N:-
Total no. of valence electrons of N in Free State = 5
Total no. of non-bonding pair electrons (or lone pair) = 0
Total no. of bonding electrons = 8
Formal charge = [5] – [0] – 1/2 [8]
Formal charge = 5 – 4 = +1
-Formal charge on O (1):-
Total no. of valence electrons of O in Free State = 6
Total no. of non-bonding pair electrons (or lone pair) = 4
Total no. of bonding electrons = 4
Formal charge = [6] – [4] – 1/2 [4]
Formal charge = 6 – 6 = 0
-Formal charge on O (2):-
Total no. of valence electrons of O in Free State = 6
Total no. of non-bonding pair electrons (or lone pair) = 6
Total no. of bonding electrons = 2
Formal charge = [6] – [6] – 1/2 [2]
Formal charge = 6 – 7 = -1
-Formal charge on O (3):-
Total no. of valence electrons of O in Free State = 6
Total no. of non-bonding pair electrons (or lone pair) = 6
Total no. of bonding electrons = 2
Formal charge = [6] – [6] – 1/2 [2]
Formal charge = 6 – 7 = -1

Note:
-Remember that formal charge is calculated because it is important for establishing and predicting the reactivity of the ion or molecule.
-It helps in the selection of the lowest energy structure which is helpful in predicting the major product of a reaction.