Question

Write three resonance structures for hydrazoic acid, \(\mathrm{HN}_{3}\). The atomic arrangement is HNNN. Show formal charges.

Short answer

The resonance structures of hydrazoic acid (HN3) are three: \[ \mathrm{H-N=N=N}, \mathrm{H=N-N\:^{-}-N\:^{+}}, \mathrm{H\:^{-}-N\:^{+}-N=N} \] The formal charges on Nitrogen atoms in these structures are respectively: \[ \{(0, 0, 0), (-1, 0, +1), (+1, 0, -1)\} \]

Step-by-step solution

Draw a valid Lewis structure

Initially, start by drawing a valid Lewis structure for hydrazoic acid. In this structure, the Hydrogen is bonded to the first Nitrogen, and Nitrogen atoms are connected consecutively. Each Nitrogen atom must have 5 valence electrons (as per the periodic table), and hydrogen must have one valence electron. Use these rules to position the other electrons around the atoms.

Draw Resonance Structures

Based on the initial Lewis representation, make changes where the double bond can flip between Nitrogen atoms, thereby creating resonance structures. This leads to redistribution but not total count of electrons. Add a double bond between 2nd and 3rd Nitrogen atoms and remove one from 1st and 2nd. This will form the second resonance structure. Similarly, make the third resonance by forming double bond between 1st and 2nd Nitrogen again but this time remove lone pair of electron from 1st Nitrogen and put it as lone pair to third. This satisfies the octet rule where each Nitrogen atom is surrounded by 8 electrons and hydrogen by 2 electrons.

Establish Formal Charges

Formal charges for each atom in all three structures will be determined. The formal charge of any atom can be found using the equation: Formal charge = (number of valence electrons) - (non-bonding valence electrons + number of bonds). Apply this formula to each atom in your resonance structures. This ensures that the overall charge of each structure is consistent with the actual molecule.