Question

Three known isomers exist of \(\mathrm{N}_{2} \mathrm{CO},\) with the atoms in these sequences: \(\mathrm{NOCN} ; \mathrm{ONNC} ;\) and ONCN. Write resonance structures for each isomer and use formal charge to predict which isomer is the most stable.

Short answer

ONCN is the most stable isomer due to a more favorable formal charge distribution.

Step-by-step solution

Write the Lewis structure for NOCN

To write the Lewis structure for \(\mathrm{NOCN}\), place each atom in sequence: \(\mathrm{N}-\mathrm{O}-\mathrm{C}-\mathrm{N}\). Start with single bonds and distribute the remaining valence electrons to satisfy the octet rule. Calculate formal charges using the formula: \(\text{Formal Charge} = \text{(Valence electrons - Non-bonding electrons - Half of bonding electrons)}\).- Assign pairs of dots to represent electrons around each atom and adjust bonds to minimize formal charges.

Write Resonance Structures for NOCN

Create possible resonance structures for \(\mathrm{NOCN}\). Possible structures include multiple bonds between different atoms like \(\mathrm{N}=\mathrm{C}-\mathrm{N}\), with changes in locations of double bonds or lone pairs. Evaluate the formal charges for each resonance structure to determine if there are alternative significant contributors that redistribute charge better.

Write the Lewis structure for ONNC

For \(\mathrm{ONNC}\), place the atoms as \(\mathrm{O}-\mathrm{N}-\mathrm{N}-\mathrm{C}\). Begin with single bonds, then distribute the remaining valence electrons. Calculate formal charges for each atom and adjust bonds to achieve minimal formal charges. This might involve creating multiple bonds, especially between the \(\mathrm{N}-\mathrm{C}\).

Write Resonance Structures for ONNC

Create resonance structures for \(\mathrm{ONNC}\), where electrons may be shifted, and bonds altered (such as \(\mathrm{O}\equiv\mathrm{N}-\mathrm{N}\equiv\mathrm{C}\)). Calculate and compare the formal charges for each structure to find potentially stable options.

Write the Lewis structure for ONCN

Arrange the atoms in the sequence \(\mathrm{O}-\mathrm{N}-\mathrm{C}-\mathrm{N}\) for \(\mathrm{ONCN}\). Establish single bonds initially and then distribute valence electrons. Employ the formula for formal charges to optimize electron distribution, achieving a stable configuration with minimal formal charges on atoms.

Write Resonance Structures for ONCN

Develop resonance structures for \(\mathrm{ONCN}\), exploring possibilities like \(\mathrm{O}\equiv\mathrm{N}-\mathrm{C}\equiv\mathrm{N}\). Determine the formal charge of each possibility to see if any alterations provide a favorable spread of electrons and charge distribution.

Evaluating Stability Based on Formal Charge

Compare the resonance structures for all isomers. Analyze formal charges: Isomers with formal charges close to zero are more stable. Look for structures where charges are on atoms with compatible electronegativity.

Key concepts

Lewis Structures

Lewis structures are essential tools in chemistry. They help us visualize molecules and predict their behavior. When drawing a Lewis structure, we start by arranging atoms in the molecule. Each atom is connected by bonds, generally starting with single bonds. After the atoms are placed and bonded, we use valence electrons to satisfy each atom's octet (or duet for hydrogen).

• Count the total number of valence electrons in the molecule.
• Place the atoms in the correct sequence and connect them with bonds.
• Distribute the remaining electrons to complete the octet for each atom.

In the molecule \( ext{NOCN}\), for instance, you arrange them linearly as N-O-C-N, then use dots to show the remaining valence electrons around each atom. Understanding how to correctly draw the Lewis structure is crucial, as this forms the basis for identifying possible resonance structures.

Formal Charge

Formal charge is a concept used to assess the distribution of electrons in a molecule. It helps in evaluating which resonance structures are more likely to contribute to the actual structure of the molecule. The formula used to calculate formal charge is simple: \( \text{Formal Charge} = \text{(Valence electrons - Non-bonding electrons - Half of bonding electrons)}\).

• Aim to have formal charges close to zero for greater stability.
• If formal charges are unavoidable, negative charges should reside on more electronegative atoms.
• Calculation of formal charge helps identify which resonance structures are the most stable.

By calculating formal charges, we can compare structures such as for NOCN, ONNC, and ONCN. This comparison helps us assess which isomer has the most favorable electron distribution, impacting which isomer is the most stable.

Isomer Stability

Isomer stability refers to how energetically favorable a molecule’s structure is. Stability depends on factors like bond strength, molecular geometry, and electron distribution. In cases with resonance structures, analyzing formal charges gives insight into isomer stability. The more stable an isomer, the lower its potential energy and reactivity.

• Stability is increased when there are stronger bonds and minimal charge separation.
• Electronegative atoms should ideally carry negative formal charges.
• Structures closest to satisfying the octet rule without excessive charge separation are generally more stable.

For the isomers of \(\mathrm{N}_{2} \mathrm{CO}\), comparing stability means checking which arrangement leads to desirable bonding and minimal formal charges. This understanding is key in determining which isomer is most abundant or reactive.

Valence Electrons

Valence electrons are the outermost electrons of an atom. They play a key role in chemical bonding and reactions. When determining Lewis structures and resonance, knowing the number of valence electrons helps in distributing the electrons correctly.

• Identify the group number from the periodic table to find the valence electrons for most elements.
• Use these electrons to form bonds and lone pairs around atoms.
• Ensure that for most atoms, the total number of bonds and lone pair electrons satisfies the octet rule.

Proper distribution of valence electrons ensures that resonance structures are valid. For \(\text{NOCN}\), ONNC, and ONCN, correctly evaluating the number of valence electrons available is crucial for drawing valid resonance structures and predicting the molecule's reactivity and properties.