Question

Specify which atoms, if any, bear a formal charge in the Lewis structure given and the net charge for the species.

Answer 1

Answer :

Formal charge on C:  (-1)

Formal charge on N:  (0)

Net charge: (-1)

Explanation :

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

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, $CN^-$

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

Therefore, the total number of valence electrons in $CN^-$ = 4 + 5 + 1= 10

According to Lewis-dot structure, there are 6 number of bonding electrons and 4 number of non-bonding electrons.

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

Formula for formal charge :

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

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

$\text{Formal charge on N}=5-2-\frac{6}{2}=0$

Net charge = -1 + 0 = -1