10.16 P - Chemistry: Molecular Nature Of Matter And Change

Question

Draw the Lewis structure with the lowest formal charges, and determine the charge of each atom in 

(a)  ${{\mathbf{BF}}_4}^{-}$

(b)  $\mathbf{\text{ClNO}}$

Step-by-Step Solution

Answer

The Lewis structure of

a. ${{\mathbf{BF}}_4}^{-}$ = Linear shape with central atom B-atom having +3 charge and have +1 formal charges.

                               

b.$\mathbf{ClNO}$ = bent shape with central atom N-atom having +3 charge and have 0 formal charges.

 

    

 

Lewis Structure

A Lewis structure can be defined as the basic structure of a molecule that used the valence electron of each atom involved. In Lewis’s structure, the least electronegative atom will be the central atom. 

 

Formal Charge is a theoretical concept that is also called fake charge. It is the charge which is dispersed on the whole molecule, not on the single atom.

Formal Charge = Valence electron – Lone pair electron – ½ (Bonded electron)

 

Explanation

B-atom belongs to group 13 having 3 electrons in the valence required to give or take 5 electrons to fulfill its octet whereas F-atom belongs to group 17 having 7 electrons in the valence shell and requires 1 electron to fulfill the octet. In Lewis’s structure, the octet of B-atom is completed by the 4 electrons provided by F-atom and one extra electron from the molecule. 

                                         

 

Formal Charge of each atom:

 $\begin{array}{c}\mathbf{Formal}\mathbf{ }\mathbf{charge}\mathbf{ }\mathbf{on}\mathbf{ }\mathbf{Boron}\mathbf{=}\left(\mathbf{5}\mathbf{–}\mathbf{0}\mathbf{–}\frac{8}{2}\right)\mathbf{=}\mathbf{1}\\ \mathbf{Formal}\mathbf{ }\mathbf{charge}\mathbf{ }\mathbf{on}\mathbf{ }\mathbf{4}\mathbf{ }\mathbf{Fluorine}\mathbf{=}\left(\mathbf{7}\mathbf{–}\mathbf{6}\mathbf{–}\frac{2}{2}\right)\mathbf{=}\mathbf{0}\end{array}$

Clarification

Cl belongs to the group 17 having 7 electrons in the valence requires to give or take 1 electrons to fulfil its octet, O-atom belongs to group 16 having 6 electrons in valence shell and requires 2 electron to fulfil octet and N-atom belongs to group 15 having 5 electrons in valence shell and requires 3 electrons to fulfil octet.  In Lewis structure, Octet of N-atom is fulfilled by the 1 electron from Cl-atom and 2 electrons from oxygen forming single and double bond respectively. 

                                                  

 

Formal Charge of each atom:

 $\begin{array}{l}\mathbf{Formal}\mathbf{ }\mathbf{charge}\mathbf{ }\mathbf{on}\mathbf{ }\mathbf{Chlorine}\mathbf{=}\mathbf{7}\mathbf{–}\mathbf{6}\mathbf{–}\frac{2}{2}\mathbf{=}\mathbf{0}\\ \begin{array}{l}\mathbf{Formal}\mathbf{ }\mathbf{charge}\mathbf{ }\mathbf{on}\mathbf{ }\mathbf{Oxygen}\mathbf{=}\mathbf{6}\mathbf{–}\mathbf{6}\mathbf{–}\frac{2}{2}\mathbf{=}\mathbf{-}\mathbf{1}\\ \mathbf{Formal}\mathbf{ }\mathbf{charge}\mathbf{ }\mathbf{on}\mathbf{ }\mathbf{Nitrogen}\mathbf{=}\mathbf{5}\mathbf{–}\mathbf{2}\mathbf{–}\frac{6}{2}\mathbf{=}\mathbf{0}\end{array}\end{array}$