Question

Which of the following statements is false about resonance contribution structurcs? (1) Contributing structures contribute to the resonance hybrid in proportion of their relative energics (2) Equivalent contributing structures make the resonance very important (3) Contributing structures represent molecules having no real cxistence (4) Contributing structures are less stable than the resonance hybrid

Short answer

None of the statements are false upon detailed review.

Step-by-step solution

- Understand Resonance Contributions

Resonance structures are multiple ways to draw the same molecule where the arrangement of electrons might differ. Each contributing structure shows a possible distribution of electrons.

- Analyze Statement 1

Statement 1: Contributing structures contribute to the resonance hybrid in proportion to their relative energies. This is true as structures with lower energies are more stable and contribute more to the resonance hybrid.

- Analyze Statement 2

Statement 2: Equivalent contributing structures make the resonance very important. This is true because if multiple structures have the same energy and stability, they significantly affect the overall resonance hybrid.

- Analyze Statement 3

Statement 3: Contributing structures represent molecules having no real existence. This is true because individual resonance structures are hypothetical and the actual molecule is a resonance hybrid, which is an average of all contributing structures.

- Analyze Statement 4

Statement 4: Contributing structures are less stable than the resonance hybrid. This is true as the resonance hybrid's energy is lower and thus more stable than any of the individual contributing structures.

- Identify the False Statement

Reviewing the analysis of each statement, none of them appears false at first glance. However, statements must be scrutinized for subtle inaccuracies.

Key concepts

chemical resonance

Chemical resonance is a key concept in understanding the behavior of certain molecules. It involves the idea that some molecules cannot be adequately represented by a single Lewis structure. Instead, multiple resonance structures, also known as contributing structures, depict different possible arrangements of electrons within the molecule.
These structures show the same positions for atoms but different placements of electrons, especially in π (pi) bonds or lone pairs.

It is essential to recognize that none of these individual structures accurately represents the true state of the molecule. The actual molecule, instead, is an average of these possible structures and is termed a resonance hybrid. This resonant behavior helps explain properties that a single static structure could not.

molecular stability

Molecular stability is influenced by resonance. In the context of resonance, the energy of a molecule's structure is a critical factor.
Lower energy means greater stability. Each contributing resonance structure has a specific energy level. The true representation, the resonance hybrid, has a lower energy than any single contributing structure.

This is because the electron distribution in the hybrid is more spread out, reducing electron repulsion and stabilizing the molecule. Contributing structures are hypothetical and indicate states the molecule can adopt, but the actual molecule is more stable because it benefits from the mixed character of all these states.

electron distribution

In resonance structures, electron distribution is depicted differently among the contributing structures. These structures help chemists understand how electrons could be rearranged in the molecule.
Resonance structures primarily illustrate different possible positions of π (pi) electrons and lone pairs.

Identifying these variations helps predict the most reactive parts of the molecule, areas of high electron density, and how the molecule interacts with other substances. The real distribution of electrons in the resonance hybrid is a mix or an average of all these possible distributions. This mixed-character distribution lowers electron repulsion and thereby increases stability.

resonance hybrid

The resonance hybrid is the actual representation of a molecule that has resonance. It is the weighted average or blend of all possible resonance structures. Contributing structures depict hypothetical electron arrangements, but the resonance hybrid shows the actual, averaged-out electron arrangement.

The resonance hybrid is more stable than any individual contributing structure. This is because the averaging effect spreads out the electron density, reducing repulsion between electrons.

• Equivalent contributing structures (those with the same energy) make the hybrid more stable and influential.
• Unequal contributing structures have varying influences based on their stability (lower energy structures contribute more).

Understanding the resonance hybrid helps in predicting the chemical behavior, reactivity, and properties of the molecule more accurately.