Question

Resonance structures of a molecule should have (1) nearly the same energy contents (2) same number of paired electrons (3) identical arrangement of atoms (4) all

Short answer

All the criteria listed are necessary for resonance structures.

Step-by-step solution

- Understand Resonance Structures

Resonance structures are different ways of drawing the same molecule where the arrangement of atoms remains fixed, but the distribution of electrons differs.

- Analyze the Energy Contents

Identify that for resonance structures to be significant, they must possess nearly the same energy contents, ensuring stability.

- Count Paired Electrons

Check that each resonance structure has the same number of paired electrons within the molecule.

- Verify Atom Arrangement

Ensure that the atoms have an identical arrangement in all resonance structures. Only the placement of electrons should change.

- Conclusion

Since all the criteria (nearly the same energy contents, the same number of paired electrons, identical arrangement of atoms) are essential for resonance structures, select the option that includes all these aspects.

Key concepts

Energy Contents in Molecules

In the context of resonance structures, the energy content of a molecule is an essential factor for stability.
Resonance structures are different ways of representing the same molecule by arranging electrons in various formations. To be significant, these structures must possess nearly the same energy levels. If one structure has a much higher or lower energy content than the others, it would not contribute significantly to the resonance hybrid.
Energy differences would suggest that one structure is more stable than the others, making the higher-energy ones less significant. Thus, maintaining nearly the same energy content ensures that each resonance structure equally contributes to the overall stability of the molecule.

Paired Electrons in Chemistry

Having paired electrons is another crucial criterion for resonance structures.
In chemistry, electrons tend to pair up because this arrangement is more stable. Each resonance structure of a molecule must have the same number of paired electrons to contribute equally.
If the number of paired electrons differs, it would lead to different electronic distributions that can affect the molecule's overall stability and reactivity. Consistent pairing of electrons ensures that the molecule maintains stability across its different resonance forms, making each form equally important.

Atom Arrangement in Molecules

In resonance structures, although the electrons can shift around, the arrangement of the atoms must remain consistent.
By keeping the atomic arrangement unchanged, resonance structures depict the same molecule but with different electron positions. This constancy ensures that we are not essentially creating different molecules but different electronic representations of the same molecule.
The fixed arrangement of atoms highlights that resonance structures are not isomers (molecules with the same formula but different connectivity) but merely different ways to visualize electron delocalization within a single molecule.

Molecular Stability

The stability of a molecule is the ultimate reason behind analyzing resonance structures.
Resonance structures help to depict how electrons can be delocalized over atoms, leading to a more stable molecule. The true structure of the molecule, often considered a resonance hybrid, is a combination of all possible resonance forms and is generally lower in energy than any single form.
By considering structures with nearly the same energy content, paired electrons, and identical atom arrangements, chemists ensure that they are analyzing a molecule's most stable electronic configuration. The resonance hybrid is more stable due to the delocalization of electrons, which evenly distributes the electron density, lowering the energy of the overall molecule.