Question

Explain how it is possible to avoid the concept of resonance by using molecular orbital theory.

Short answer

The concept of resonance is bypassed in Molecular Orbital (MO) theory because it provides a better depiction of electron behavior. Resonance suggests that electrons move between multiple locations, whereas in MO theory, electrons are in a superimposed state, occupying molecular orbitals spread over the molecule. Therefore, a molecule doesn't need multiple resonance structures for its representation as required in resonance theory.

Step-by-step solution

Understanding the Concept of Resonance

Resonance is a concept in chemistry where a molecule cannot be aptly described by a single Lewis structure. Instead, multiple Lewis structures, called resonance structures, are used to depict the molecule. Although resonance structures individually do not represent actual structures of the molecule, the true structure is considered to be an amalgamation of these structures. This is often simplified by representing the molecule with a resonance hybrid, where the bonding in the molecule is spread out, or delocalized, over the entire molecule.

Understanding the Concept of MO Theory

Molecular Orbital theory is an advanced method of examining bonding in molecules. It combines the atomic orbitals of the atoms in a molecule to produce new mathematical objects called molecular orbitals, which describe the behavior and energetics of electrons in molecules. In MO theory, electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the atomic nuclei in the whole molecule. This is a more sophisticated view than the localized bond approach.

Correlating MO Theory with Resonance

In resonance theory, the location of electrons and the shape of the molecule changes from one resonance structure to another, giving the impression that the molecule oscillates between forms. But MO theory, due to its quantum mechanical basis, presents a tough picture: electrons are in a superimposed state, occupying molecular orbitals that are spread (delocalized) over the entire molecule, and they do not 'jump around' or oscillate between states. Therefore, the concept of resonance is not needed when molecules are described using MO theory.

Key concepts

Understanding Resonance

In chemistry, the concept of resonance is essential for explaining how certain molecules express characteristics that one single structure cannot accurately represent. Imagine drawing a molecule with multiple ways to arrange its double bonds or lone pairs without altering the actual atomic skeleton. Each arrangement is a "resonance structure."

Resonance does not mean molecules are flipping between these structures. Instead, the reality is more of a blend, like merging colors to create a new hue. The true form of the molecule is a weighted average of all possible resonance structures. This combined view is known as a "resonance hybrid," which has properties spread across the whole molecule. This spread is referred to as "delocalization."

• Resonance structures: Different ways to draw electron arrangements without changing atomic positions.
• Resonance hybrid: The true structure— a mix of all resonance forms.
• Delocalization: Electrons are dispersed across the molecule, not confined to a single position.

Atomic Orbitals and Molecular Bonding

Atomic orbitals are regions around the nucleus of an atom where electrons are likely to be found. Each element has its own unique set of atomic orbitals—think of them as invisible clouds where electrons hang out. They are fundamental in understanding how atoms bond and form molecules.

When atoms come together to form a molecule, their atomic orbitals overlap and combine, forming "molecular orbitals." These molecular orbitals extend over the entire molecule, allowing electrons to be shared between multiple atoms, which is the essence of bonding.

• Atomic orbitals: Specific zones around an atom where its electrons reside.
• Molecular orbitals: New orbitals forming as atoms bond, encompassing the entire molecule.
• Orbitals interact—allowing for electron sharing and molecular stability.

Through the lens of molecular orbital theory, bonding is seen as the interaction and combination of these atomic orbitals, creating a more nuanced and accurate depiction of how molecules hold together.

Delocalization in Molecular Orbitals

Delocalization is a key concept within molecular orbital theory that helps explain the distribution and behavior of electrons in molecules. Unlike in the traditional Lewis structure view, where electrons seem tied to a specific atom or bond, molecular orbital theory describes electrons as spread out over all the atoms in a molecule.

This delocalization allows electrons to be shared across the entire molecule, contributing to the molecule's stability and reactivity. It is particularly significant when discussing molecules that would traditionally require multiple resonance structures to describe their electron arrangements.

• Increased stability: Electrons are less confined, hence lowering energy.
• More accurate descriptions: Avoids jumping between resonance forms because the electrons are always in the same state.
• Greatly influences chemical properties and reactions, as electrons can flow through the entire molecular structure.

Delocalization in molecular orbitals further simplifies our understanding of molecules by offering a consistent picture of electron behavior, making the resonance approach less necessary.