Consider the hypothetical molecule B-A=B. Are the following statements true or false? (a) This molecule cannot exist. (b) If resonance was important, the molecule would have identical A–B bond lengths.

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insert step 1> Identify the type of bonds present in the molecule B-A=B. The molecule has a single bond (A-B) and a double bond (A=B).

insert step 2> Consider the possibility of the molecule's existence. For statement (a), evaluate if the molecule can exist based on the stability of the bonds and the elements involved.

insert step 3> For statement (b), consider the concept of resonance. Resonance occurs when there are multiple valid Lewis structures for a molecule. Determine if resonance is possible for B-A=B and how it would affect bond lengths.

insert step 4> Analyze the bond lengths in the context of resonance. If resonance is significant, the bond lengths between A and B would be averaged, leading to identical bond lengths.

insert step 5> Conclude the truthfulness of each statement based on your analysis of the molecule's structure and resonance possibilities.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Resonance

Resonance is a concept in chemistry that describes the delocalization of electrons in molecules where the bonding cannot be expressed by a single Lewis structure. Instead, multiple structures, known as resonance structures, contribute to the overall hybrid structure of the molecule. This delocalization can affect bond lengths and stability, leading to properties that differ from those predicted by any single structure.

Bond Lengths

Bond length refers to the average distance between the nuclei of two bonded atoms. In molecules with resonance, the bond lengths can be equalized due to the sharing of electron density across multiple structures. For example, in resonance-stabilized molecules, bonds may exhibit lengths that are intermediate between single and double bonds, reflecting the influence of resonance on molecular geometry.

Molecular Stability

Molecular stability is determined by the energy of a molecule, which is influenced by factors such as bond strength, electron delocalization, and steric interactions. Molecules that can delocalize electrons through resonance are often more stable than those that cannot, as the energy is lowered by the distribution of electron density. Understanding stability helps predict whether a hypothetical molecule can exist under normal conditions.

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