Q10.17P - Chemistry: Molecular Nature Of Matter And Change

Question

Question: Draw a Lewis structure for a resonance form of each ion with the lowest possible formal charges, show the charges, and give oxidation numbers of the atoms: 

a)  BrO₃

b)  SO₃ ^2-.

Step-by-Step Solution

Answer

Answer

 

The Lewis structure of

1. BrO₃  = Tetrahedral shape having formal charge of the central atom +2 and the oxidation number of Br is -1.
2. SO₃ ^2-. = Trigonal Planar shape having formal charge of the central atom 0 and the oxidation number of S is -2.

 

Step 1: Lewis Structure

 

Lewis structure is also known as Lewis dot structures are diagrams that show the bonding between atoms of a molecule, as well as the lone pairs electrons that may exist in the molecule. 

 

Formal Charge is a theoretical concept which 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)

 

The Oxidation number is generally representing the gain and loss of the valence electron of an atom in a molecule. 

 

Step 2: Explanation for BrO 3

(a)

 

Br-atom belongs to the group 17 having 7 electrons in the valence requires to give or take 1 electron to fulfil its octet whereas O-atom belongs to group 16 having 6 electrons in valence shell and requires 2 electrons to fulfil octet. In Lewis structure, the octet of Br-atom is completed by the 5 electrons provided by O-atom and one lone pair electron from molecule. 

                                                

Formal Charge of each atom:        

 $$\begin{gathered} \text{Formal charge on}Br-\text{atom}=\left(7--2--\frac{6}{2}\right) \\ =2 \end{gathered}$$

 

Oxidation number of the BrO₃  is -1

Step 3: Clarification for SO 3 2-

(b)

 

S-atom and O-atom belongs to group 16 having 6 electrons in valence shell and requires 2 electrons to fulfil octet. In Lewis structure, Octet of S-atom is fulfilled by the 2 electrons from 1 O-atom and 2 electrons from 2 O-atom forming double and single bond respectively

Formal Charge of each atom:

 $$\begin{gathered} \text{Formal charge on Sulphur}=\left(6--4--\frac{4}{2}\right) \\ =0 \end{gathered}$$

 

 

The oxidation number of the  SO₃ ^2- is -2.