Advanced Placement (AP) Chemistry Practice Exam

What are resonance structures?

1. Structures with a unique valence configuration

2. Structures that cannot be represented accurately by a single Lewis structure

3. Structures that depict ionic bonding exclusively

4. Structures that represent a kaleidoscope of molecular forms

The correct answer is: Structures that cannot be represented accurately by a single Lewis structure

Resonance structures are an essential concept in chemistry, particularly when dealing with molecules that cannot be accurately represented by a single Lewis structure. These structures illustrate the delocalization of electrons within a molecule, reflecting that the actual structure is a hybrid, or average, of multiple contributing structures. When a molecule has resonance structures, it indicates that there are different ways to arrange the electrons and bonds that still correctly adhere to the rules of bonding and valence. Each resonance structure contributes to the overall stability and properties of the molecule, and the real structure is a blend of all possible configurations. This is especially relevant in cases where resonance contributes to the stability of the molecule through the delocalization of pi electrons, as seen in compounds like benzene. The correct understanding of resonance structures highlights the limitations of Lewis structures in capturing the true nature of molecular bonding. Thus, the key reason for choosing the second option is that it accurately conveys the concept of resonance as a way to represent molecules that cannot be adequately captured by a single structural formula.