Chapter 9, Problem 9.57QP

Write three resonance structures for hydrazoic acid, HN₃. The atomic arrangement is HNNN. Show formal charges.

Interpretation Introduction

Interpretation: The resonance structure of the hydrazoic acid molecule should be found.

Concept Introduction: Sometimes the chemical bonding of a molecule cannot be represented using a single Lewis structure. In these cases, the chemical bonding are described by delocalization of electrons and is known as resonance.

In some molecules, there is possibility of more than one Lewis structure where all the structures are equally acceptable. One of the acceptable Lewis structures of these molecules is called resonance structure.

All the possible resonance structures are imaginary whereas the resonance hybrid is real.

Any of the possible structure does not exist as such like a stable real molecule. So it is not possible to isolate one resonance structure.

These structures will differ only in the arrangement of the electrons not in the relative position of the atomic nuclei.

Structure with greater number of covalent bonds are more stable comparing to that with lower number of covalent bonds.

Structure which does not involve charge separation is more stable when comparing with structure having positive and negative charge separation.

While drawing resonance structure of a molecule some rules should be followed where the position, over whole charge and chemical framework remains intact. Also only π and nonbonding electron has been moved in all the three resonance structures

Answer to Problem 9.57QP

The given atomic arrangement of $\text{hydrazoic}$ acid is $\text{HNNN}$.

Resonance structure of hydrazoic acid is drawn below.

Explanation of Solution

In the case of hydrazoic acid, the chemical bonding of a molecule cannot be represented using a single Lewis structure. The chemical bonding are described by delocalization of electrons forming 3 possible resonance structures. In all the 3 resonance structures the position, over whole charge and chemical framework remains intact.

Conclusion

The resonance structures of the hydrazoic acid molecule were drawn.

Interpretation Introduction

Interpretation: The formal charges of hydrazoic acid molecule should be found.

Concept Introduction

A formal charge (FC) is the charge assigned to an atom in a molecule, irrespective of relative electronegativity by thinking that electrons in all chemical bonds are shared equally among atoms.

This method is used to identify the most probable Lewis structures if more than one possibility exists for a compound.

The Lewis structure with formal charge on each of the atoms close to zero is taken as the most plausible structure.

Formal charge of an atom can be determined by the given formula.

$\text{Formal}\text{charge}\left(\text{F}\text{C}\right)\text{=}\left(\begin{array}{l}\text{no}\text{.of}\text{valence}\\ \text{electron}\text{in}\text{atom}\end{array}\right)-\frac{\text{1}}{\text{2}}\left(\begin{array}{l}\text{no}\text{.of}\text{bonding}\\ \text{electrons}\end{array}\right)-\left(\begin{array}{l}\text{no}\text{.of}\text{non-bonding}\\ \text{electrons}\end{array}\right)$

Answer to Problem 9.57QP

Formal charge for the given resonance structure is given below

Explanation of Solution

The formal charge of the given compound is calculated,

• Hydrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=1}\\ \text{Number}\text{of}\text{bonding}\text{electron=}2\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}0\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}1-\left(\frac{\text{1}}{\text{2}}\text{×2}\right)\\ \text{=0}\end{array}$

• First nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}6\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}2\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}5-\left(\frac{\text{1}}{\text{2}}\text{×6}\right)-2\\ \text{=0}\end{array}$

• Second nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}8\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}0\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}5\text{-}\left(\frac{\text{1}}{\text{2}}\text{×8}\right)\\ \text{=+1}\end{array}$

• Third nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}4\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}4\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}\text{5}-\left(\frac{\text{1}}{\text{2}}\text{×4}\right)-\text{4}\\ \text{=}-\text{1}\end{array}$

Formal charge of the given resonance structure is given below

The formal charge of the given compound is calculated,

• Hydrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=1}\\ \text{Number}\text{of}\text{bonding}\text{electron=}\text{2}\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}\text{0}\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}1\text{-}\left(\frac{\text{1}}{\text{2}}\text{×2}\right)\\ \text{=0}\end{array}$

• First nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}4\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}4\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}5-\left(\frac{\text{1}}{\text{2}}\text{×4}\right)-4\\ \text{=}-\text{1}\end{array}$

• Second nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}8\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}0\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}5\text{-}\left(\frac{\text{1}}{\text{2}}\text{×8}\right)\\ \text{=+1}\end{array}$

• Third nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}6\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}2\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}5-\left(\frac{\text{1}}{\text{2}}\text{×6}\right)-2\\ \text{=0}\end{array}$

Formal charge of the given resonance structure is given below

The formal charge of the given compound is calculated,

• Hydrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=1}\\ \text{Number}\text{of}\text{bonding}\text{electron=}\text{2}\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}\text{0}\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}1\text{-}\left(\frac{\text{1}}{\text{2}}\text{×2}\right)\\ \text{=0}\end{array}$

• First nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}4\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}4\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}5-\left(\frac{\text{1}}{\text{2}}\text{×4}\right)-4\\ \text{=}-\text{1}\end{array}$

• Second nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}8\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}0\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}5\text{-}\left(\frac{\text{1}}{\text{2}}\text{×8}\right)\\ \text{=+1}\end{array}$

• Third nitrogen atom

$\begin{array}{c}\text{Number}\text{of}\text{valence}\text{electron=5}\\ \text{Number}\text{of}\text{bonding}\text{electron=}6\\ \text{Number}\text{of}\text{non-bonding}\text{electron}\text{=}2\end{array}$

Substituting these values to the equation,

$\begin{array}{c}\text{FC}\text{=}5-\left(\frac{\text{1}}{\text{2}}\text{×6}\right)-2\\ \text{=0}\end{array}$

Conclusion

The formal charges of hydrazoic acid molecule were shown.