Question

Resonance structures of a molecule does not have (a) Identical arrangement of atoms (b) Nearly the same energy content (c) Same number of paired electrons (d) Identical bonding

Short answer

Resonance structures do not have identical bonding (option d).

Step-by-step solution

Understand Resonance Structures

Resonance structures are different ways of drawing the same molecule, showing possible configurations of electron positions while keeping the atom positions the same. They depict the delocalization of electrons in molecules. This is crucial to note, as it affects our understanding of what is held constant across resonance structures.

Identify What Resonance Structures Share

Resonance structures must have identical arrangement of atoms because they are different representations of the same molecule. They also have to have the same number of electron pairs and roughly the same energy content, as they are different ways to depict the electron delocalization in a molecule. These aspects cannot vary between resonance structures.

Recognize What Resonance Structures Lack

What can vary between resonance structures is the positions of the electrons, which can lead to differences in bonding representation. The actual bond order could be different in each structure, leading to non-identical bonding depiction. This is the characteristic that resonance structures do not have.

Evaluate the Options

From the steps above, analyze the given options: (a) Identical arrangement of atoms: must be identical across resonance structures. (b) Nearly the same energy content: approximately the same energies are needed for resonance. (c) Same number of paired electrons: must remain constant to keep valency consistent. (d) Identical bonding: varies due to different delocalized electron positions.

Key concepts

Electron Delocalization

Electron delocalization refers to electrons that are not confined to a single, fixed location in a molecule. Instead, they are spread over several atoms, allowing certain molecules to have multiple valid Lewis structures called resonance structures. These structures are simply different ways of representing the same molecule by showing how the electrons could be arranged. It's important to understand that these are not different molecules, but rather various depictions of electron distribution.

• Delocalization enhances molecular stability, as electrons can lower the energy of the molecule by residing in lower-energy molecular orbitals.
• This concept helps explain why some molecules exhibit special properties, such as increased electrical conductivity in metals or aromaticity in benzene.

This flexibility in arrangement does not affect the placement of atoms themselves; thus, the atoms remain stationary while the valence electrons move about, contributing to a molecule's stability and overall behavior.

Bond Order

Bond order reflects the number of shared electron pairs between two atoms. In the context of resonance structures, bond order gives insight into the stability and strength of a molecule's bonds. Resonance hybrids, which are the actual structures that molecules exhibit, tend to have intermediate bond orders as they represent a blend of all resonance structures.

• To calculate bond order: Sum up the bond orders in all resonance structures and divide by the number of contributing structures.
• Higher bond orders usually imply stronger and shorter bonds, suggesting higher molecular stability.

Understanding bond order is crucial, as it helps predict molecular shape, bond strength, and reactivity. For instance, in a molecule like ozone (O₃), the bond orders between the oxygen atoms are not integers, indicating the presence of resonance.

Molecular Configuration

Molecular configuration refers to the fixed spatial arrangement of atoms within a molecule. In the case of resonance structures, while the arrangement of electrons changes, the molecular configuration does not. This means the core structure of where atoms are situated remains unchanged across different resonance forms.

• Confers to physical properties of the molecule unaffected by the electron movement.
• Defines how molecules interact and bond with other molecules, crucial in determining biochemical pathways and reactions.

Molecular configuration is a pivotal aspect of stereochemistry, as it distinguishes between different isomers and helps determine the molecule's function and interaction capabilities in chemical processes.

Energy Content in Molecules

The energy content in molecules is closely linked to their stability. Resonance structures typically possess nearly equal energy levels, reflecting the energy in these forms when electrons are delocalized across atoms. While individual resonance structures display varying energies, the resonance hybrid—a real representation of the molecule—results in a lower energy state compared to any single resonance structure.

• Molecules strive to reach the lowest possible energy state, hence favoring resonance where possible.
• Stability is a direct result of distributing electron density evenly, reducing potential energy inconsistencies.

This concept is significant in understanding why molecules behave the way they do, particularly in reactions where energy changes lead to products that are more stable than the reactants. Highlighting the balance of energy content helps in grasping reaction mechanisms, particularly those involving large organic molecules.