Question

Consider the hypothetical molecule \(\mathrm{B}-\mathrm{A}=\mathrm{B}\) . 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.

Short answer

Statement (a) cannot be definitively considered true or false due to insufficient information on the molecule's thermodynamic stability and electronic configuration. Statement (b) is true because if there were any resonance in the hypothetical molecule \(\mathrm{B}-\mathrm{A}=\mathrm{B}\), it could affect the \(A-B\) bonds, making them equivalent. However, resonance is not important for this molecule as there are no alternative resonance structures.

Step-by-step solution

Statement (a): This molecule cannot exist.

To determine whether the hypothetical molecule \(\mathrm{B}-\mathrm{A}=\mathrm{B}\) could exist, we can refer to the rules of chemistry and bonding. A molecule's existence often depends on its thermodynamic stability and/or the electronic configuration of the atoms involved. However, there isn’t sufficient information provided to conclude the molecule can’t exist. Hence, we cannot definitively consider this statement true or false.

Statement (b): If resonance was important, the molecule would have identical \(A-B\) bond lengths.

Resonance occurs when a molecule can be represented by more than one Lewis structure, having the same arrangement of atoms but different distributions of electrons. The actual molecule will be a resonance hybrid of these structures, leading to some averaged properties, such as bond length and bond strength. For the hypothetical molecule \(\mathrm{B}-\mathrm{A}=\mathrm{B}\), there are no alternative ways to distribute the electrons that would lead to different resonance structures while maintaining the same atomic arrangement. Thus, resonance is not important for this molecule. However, if there were any resonance, that could affect the \(A-B\) bonds, making them equivalent. Hence, this statement is true.

Key concepts

Resonance Structures

Resonance structures are a key concept in understanding the behavior and properties of many molecules in chemistry. When a molecule can be depicted with more than one valid Lewis structure, differing only in the distribution of electrons but not the arrangement of atoms, these are known as resonance structures. These structures are important because they describe the molecule as an average, called a resonance hybrid, which can have properties different from any individual resonance structure.

In cases where resonance is significant, this can lead to equalization of bond lengths. For example, if a molecule has two bonds between the same pairs of atoms that are part of different resonance structures, through resonance, these bonds can exhibit equal lengths. However, not all molecules have resonance, especially if there are no alternative ways to rearrange the electrons to provide additional resonance structures. In these instances, resonance does not play a role in the characteristics of the molecule, as is the case in the hypothetical molecule \( \mathrm{B}-\mathrm{A}=\mathrm{B} \).

The appearance of resonance usually results in greater stability due to electron delocalization, which lowers the system's energy. This is a demonstrated phenomenon in many known systems, providing important insights into the molecular structure and reactivity.

Thermodynamic Stability

The concept of thermodynamic stability is crucial in determining whether a molecule can exist or not. A molecule is considered to be thermodynamically stable if it has lower energy than its potential decomposition products. In other words, it should not spontaneously decompose into other substances under given conditions. This stability often depends on the surrounding environment of the reaction or the conditions it is subjected to, such as temperature and pressure.

Thermodynamic stability is often evaluated in terms of the energy change associated with the formation or decomposition of a molecule. If a molecule has high thermodynamic stability, it will require significant energy to break its bonds, making it less reactive and longer-lasting. Conversely, low thermodynamic stability indicates that a molecule might spontaneously arrange or decompose, indicating higher reactivity. This conceptual framework is often applied in assessing the existence and vocation of a molecule, especially hypothetical ones like \( \mathrm{B}-\mathrm{A}=\mathrm{B} \). Without specific information on energy levels and reactivity for this particular molecule, we can't definitively determine the truthfulness of its potential existence.

In experimental chemistry, looking at energy diagrams and calculating Gibbs free energy changes often helps scientists infer the stability and viability of a molecule or chemical reaction.

Electronic Configuration

Understanding the electronic configuration of the atoms involved in a molecule is a fundamental part of predicting and explaining chemical bonding and molecule stability. Electronic configuration refers to the distribution of electrons in an atom's orbitals, following principles such as the Pauli exclusion principle and Hund's rule. This distribution determines how atoms will bond together and form compounds.

• Atoms strive for a full valence shell, often achieving this through sharing, gaining, or losing electrons, which is the driving force behind chemical bonds.
• The type of bond formed—be it ionic, covalent, or metallic—depends significantly on the electronic configurations of the atoms involved.
• Electronic configuration can also predict the ability of a molecule to form resonance structures, as it determines how electrons can be rearranged without altering atomic positions.

Evaluating the electronic configuration of each atom in the hypothetical molecule \( \mathrm{B}-\mathrm{A}=\mathrm{B} \) would shed more light on its bonding structure and potential existence. For instance, if \( \mathrm{A} \) is capable of forming stable bonds with two \( \mathrm{B} \) atoms following its electronic configuration, the molecule may feasibly exist.

In chemistry education, understanding electronic configurations helps students foresee how atoms interact to form stable, resonance-capable structures, directly linking to overarching principles of chemical bonding and molecule formation.