Question

In the best Lewis structure for the fulminate ion, CNO–, what is the formal charge on the central nitrogen atom?

Answer 1

Answer : The formal charge on the central nitrogen atom is, (+1)

Explanation :

Resonance structure : Resonance structure is an alternating method or way of drawing a Lewis-dot structure for a compound.

Resonance structure is defined as any of two or more possible structures of the compound. These structures have the identical geometry but have different arrangements of the paired electrons. Thus, we can say that the resonating structure are just the way of representing the same molecule.

First we have to determine the Lewis-dot structure of $CNO^-$.

Lewis-dot structure : It shows the bonding between the atoms of a molecule and it also shows the unpaired electrons present in the molecule.

In the Lewis-dot structure the valance electrons are shown by 'dot'.

The given molecule is, $CNO^-$

As we know that carbon has '4' valence electrons, nitrogen has '5' valence electrons and oxygen has '6' valence electrons.

Therefore, the total number of valence electrons in $CNO^-$ = 4 + 5 + 6 + 1= 16

According to Lewis-dot structure, there are 8 number of bonding electrons and 8 number of non-bonding electrons.

Now we have to determine the formal charge for each atom.

Formula for formal charge :

$\text{Formal charge}=\text{Valence electrons}-\text{Non-bonding electrons}-\frac{\text{Bonding electrons}}{2}$

For structure 1 :

$\text{Formal charge on O}=6-6-\frac{2}{2}=-1$

$\text{Formal charge on C}=4-2-\frac{6}{2}=-1$

$\text{Formal charge on N}=5-0-\frac{8}{2}=+1$

For structure 2 :

$\text{Formal charge on O}=6-4-\frac{4}{2}=0$

$\text{Formal charge on C}=4-4-\frac{4}{2}=-2$

$\text{Formal charge on N}=5-0-\frac{8}{2}=+1$

For structure 3 :

$\text{Formal charge on O}=6-2-\frac{6}{2}=+1$

$\text{Formal charge on C}=4-6-\frac{2}{2}=-3$

$\text{Formal charge on N}=5-0-\frac{8}{2}=+1$

The best Lewis-dot structure is, structure 1.

Thus, the formal charge on the central nitrogen atom is, (+1)