Question

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

Short answer

HN₃ has three resonance structures: H-N≡N-N⁻, H-N⁻=N=N⁰, H⁰-N-N⁺≡N²⁻.

Step-by-step solution

Understanding Resonance Structures

In resonance structures, atoms are arranged in the same pattern but the placement of electrons differs. For hydrazoic acid (HN₃), you'll draw Lewis structures: the hydrogen (H) connected to a nitrogen atom, followed by two more nitrogen atoms connected sequentially (H-N-N-N). Then, distribute the electrons to fulfill the octet rule and minimize formal charges.

Drawing the First Resonance Structure

Begin drawing the first structure by arranging the atoms: H on one end, followed by three sequential N atoms. Form a triple bond between the first and second N and a single bond between the second and third N. Assign the remaining electrons to complete octets and determine formal charges. This gives H-N≡N-N- with formal charges of 0 on H, +1 on the second N, 0 on the third N, and -1 on the last N.

Drawing the Second Resonance Structure

For the second resonance structure, rearrange the pi (π) electrons by shifting a lone pair from the N atoms. Form a double bond between the first two N atoms and a double bond with the subsequent N. It results in the structure H-N=N=N with formal charges: H (0), first N (0), second N (0), and last N (-1).

Drawing the Third Resonance Structure

In the third structure, change the bonding so there's a single bond connecting H and the first N, a double bond between the second and third N atoms, and another single bond between them. This looks like H-N-N≡N with formal charges: H (0), first N (0), second N (+1), and third N (-2).

Evaluate and Verify Formal Charges

Check each resonance structure by calculating the formal charge for each atom using the formula: \( ext{Formal Charge} = ext{Valence Electrons} - ( ext{Lone Pair Electrons} + rac{ ext{Bonding Electrons}}{2}) \). Ensure the sum of the formal charges equals the total charge of the molecule, which is zero for HN₃.

Key concepts

Lewis Structures

Lewis structures are diagrams that represent the covalent bonds between atoms in a molecule, alongside any lone (non-bonded) electron pairs. To create a Lewis structure for a molecule, follow these steps:

• Identify and arrange the atoms in the correct sequence, often based on their connectivity or layout within a chemical formula.
• Determine the number of valence electrons for each atom and sum them up for the entire molecule.
• Distribute electrons around the atoms to fulfill the octet rule, which means most atoms will have eight electrons in their outer shell (except hydrogen, which is satisfied with two).
• Form bonds by sharing electron pairs, thus connecting the atoms.
• Adjust electron placement to create double or triple bonds as necessary, ensuring no violations of the octet rule occur.

Lewis structures provide insights into how atoms are bonded in a molecule, and help predict reactivity and chemical behavior.

Formal Charges

Formal charges are a method to assess the distribution of electrons in a molecule. They help establish the most stable Lewis structure by indicating excess or deficit of electrons on an atom. To calculate the formal charge:

Use the formula: \[ \text{Formal Charge} = \text{Valence Electrons} - (\text{Lone Pair Electrons} + \frac{\text{Bonding Electrons}}{2}) \]

• Valence Electrons: number of electrons in an atom's outer shell.
• Lone Pair Electrons: electrons not involved in bonding.
• Bonding Electrons: electrons shared between atoms.

Apply this calculation to every atom in the molecule. The goal is to have as close to zero formal charge as possible on each atom to maximize stability. The overall molecule charge should match the actual charge of the molecule.

Octet Rule

The octet rule is a key guideline for understanding electron distribution in chemical bonds. It states that atoms tend to form bonds in order to have eight electrons in their valence shell, thus achieving a stable electronic configuration similar to noble gases.

• Most atoms follow this rule in their compounds, such as carbon, nitrogen, and oxygen.
• Exceptions include hydrogen, which is stable with two electrons, and other atoms that can have expanded octets like phosphorus and sulfur.

For molecules like hydrazoic acid (HN₃), satisfying the octet rule is crucial for determining valid resonance structures. This leads to structures where formal charges are minimized and stability is enhanced, showing possible electron configurations.

Hydrazoic Acid

Hydrazoic acid, a compound with the formula \( \text{HN}_3 \), presents interesting characteristics in chemistry due to its resonance. It contains one hydrogen and three nitrogen atoms, making its structure formation intriguing for chemists.

• As a linear molecule, HN₃ can exhibit multiple resonance structures contributing to its overall stability.
• Determining the possible electron distributions helps to predict its behavior and reactions.

When drawing the resonance structures for hydrazoic acid, focus on distributing electrons such that the octet rule is fulfilled, and formal charges are balanced. This allows for the visualization of its electronic arrangement, essential for understanding its chemistry.

Pi Electrons

Pi (\(\pi\)) electrons are those found in the "p" orbitals that participate in double and triple bonds within a molecule. Unlike sigma bonds, which involve head-on overlapping, pi bonds arise from the side-to-side overlap of p orbitals. This makes them key to understanding molecular resonance.

• In resonance structures, pi electrons can be shifted to explore alternative bonding scenarios.
• These shifts allow multiple valid structures, each contributing to the molecule's stability.

For hydrazoic acid, rearranging pi electrons leads to different resonance forms. These structures suggest variability in bond strengths and electron distributions, fundamental to grasping the molecule's overall characteristics.