Question

The Lewis structure for hydrazoic acid may be written as $$ \stackrel{\mathrm{H}}{\mathrm{N}}=\mathrm{N}=\ddot{\mathrm{N}} $$

Short answer

Answer: The Lewis structure of hydrazoic acid is HN=NN=δN, with one hydrogen atom connected to the first nitrogen atom (N1) by a single bond and double bonds between N1 and N2 and N2 and N3. Lone pairs are present on N1 and N3. To construct the Lewis structure, we first identify nitrogen as the central atom, determine the total number of valence electrons (16), draw single bonds between the nitrogen atoms and the hydrogen atom, distribute the remaining valence electrons to satisfy the octet rule, and finally draw the structure with double bonds and lone pairs.

Step-by-step solution

Identify the central atom

In this case, the central atom is nitrogen (N). There are three nitrogen atoms in the hydrazoic acid molecule.

Determine the number of valence electrons in the molecule

Each nitrogen (N) atom has 5 valence electrons, and each hydrogen (H) atom has 1 valence electron. Thus, the total number of valence electrons in the molecule is: $$ 3 × 5 (N) + 1 (H) = 15 + 1 = 16 $$

Draw the single bonds for the molecule

To form the initial structure of the molecule, we will connect one nitrogen to each of the other two nitrogen atoms using single bonds. Then, we will connect one hydrogen atom to the first nitrogen atom. The first nitrogen atom (N1) will be connected to the second nitrogen atom (N2) and the hydrogen atom, while the second nitrogen atom (N2) will be connected to the third nitrogen atom (N3).

Distribute the remaining valence electrons

We have used 6 of the 16 valence electrons in the single bonds earlier. Now we need to distribute the remaining 10 valence electrons to satisfy the octet rule where possible. Each nitrogen atom needs 8 electrons to fulfill the octet rule. 1. Place one lone pair of electrons on N3, contributing 2 more electrons (total 8 electrons used). 2. Place two lone pairs of electrons on N1, contributing 4 more electrons (total 12 electrons used). Now, we have four valence electrons remaining. Instead of placing these electrons as two lone pairs on N2, put them as two double bonds between N1 and N2 and N2 and N3. This will satisfy the octet rule for all atoms.

Draw the final Lewis structure for hydrazoic acid

The final Lewis structure for hydrazoic acid is: $$ \stackrel{\mathrm{H}}{\mathrm{N}}=\mathrm{N}=\ddot{\mathrm{N}} $$ The Lewis structure shows that the nitrogen atoms are connected with double bonds, and lone pairs are present on N1 and N3. The hydrogen atom is connected to N1 with a single bond. All atoms obey the octet rule and have a complete set of valence electrons.

Key concepts

Valence Electrons

Understanding the concept of valence electrons is essential when drawing the Lewis structure of any molecule, including hydrazoic acid. Valence electrons are the electrons in the outer shell of an atom that are involved in forming bonds. Each element has a characteristic number of valence electrons related to its position in the periodic table. For instance, nitrogen (N) has five valence electrons, while hydrogen (H) has one.

When determining the Lewis structure, the first step is to count the valence electrons available for bonding. In hydrazoic acid, with the formula HN3, you have three nitrogen atoms and one hydrogen atom. Therefore, the number of valence electrons is calculated as follows:
\[ 3 \times 5 \; (\text{for N}) + 1 \; (\text{for H}) = 15 + 1 = 16 \]
These 16 valence electrons are then distributed around the atoms to form bonds and satisfy the octet rule, which is explained in the next section.

Octet Rule

The octet rule is a guiding principle in chemistry that suggests atoms tend to form bonds to have eight electrons in their valence shell, resulting in a stable electron configuration reminiscent of the noble gases. The rule applies to many main-group elements, particularly carbon, nitrogen, oxygen, and the halogens.

In the context of hydrazoic acid, the Lewis structure is dictated by the octet rule. After determining the number of valence electrons and forming single bonds between the nitrogen atoms and between the first nitrogen and the hydrogen atom, the remaining electrons must be placed to achieve full octets where possible. Steps in the creation of the Lewis structure involve distributing electrons to:

• Create a pair of double bonds between the nitrogen atoms to ensure each nitrogen has eight electrons around it.
• Assign lone pairs to the terminal nitrogen atoms to complete their octets, while keeping in regard the total count of electrons.

Hydrazoic acid's final Lewis structure illustrates how atoms share electrons through single and double bonds, as well as lone pairs, to obey the octet rule.

Molecular Geometry

Once the Lewis structure is determined adhering to the octet rule and the distribution of valence electrons, the molecular geometry of the compound can be predicted. Molecular geometry refers to the three-dimensional arrangement of the atoms within a molecule.

For hydrazoic acid, the Lewis structure illustrates linear geometry of the nitrogen atoms. The central nitrogen atom (N2) forms double bonds with the two adjacent nitrogen atoms (N1 and N3). Since there are no lone pairs on the central nitrogen, and it is bonded to two other atoms, the geometry is maintained as linear according to the VSEPR (Valence Shell Electron Pair Repulsion) theory.
To put it simply, in hydrazoic acid, the atom arrangement is linear because the electron pairs, bonded and nonbonded, are oriented to minimize repulsion and stabilize the molecule. The specific angles and lack of lone pairs on the central nitrogen reinforce this linear configuration.