Chemical Bonding: Localized and Delocalized Bonds & Electrons

 

Chemical Bonding: Localized and Delocalized Bonds & Electrons

Introduction to Chemical Bonding

Chemical bonding is a fundamental concept in chemistry that explains how atoms combine to form molecules. Bonds are formed when atoms share or transfer electrons to achieve a stable electronic configuration, often resembling the electron configuration of noble gases.

There are several types of chemical bonds, with the most common being:

Localized Bond

Delocalized Bond

1. Localized Bond

A localized bond is a type of chemical bond where the electrons are shared between two specific atoms. These bonding electrons are confined to the space between these two atoms, which means they are not free to move across other parts of the molecule. Localized bonds typically involve covalent bonds where electrons are shared in a focused manner between the bonded atoms.

Example: In a molecule of methane (CH₄), the electrons involved in bonding between each carbon and hydrogen atom are localized between those specific atoms.

This type of bonding is typically seen in:

Single bonds (sigma bonds) in simple molecules like H₂ or Cl₂.

Double and triple bonds where electron pairs are tightly shared between two atoms.

 

2. Localized Electrons

Localized electrons refer to the electrons in a bond that are confined to a specific pair of atoms in a molecule. They are not free to move around the entire molecule. These electrons remain in a fixed position, contributing to the stability of the bond between those atoms.

Example: In a water molecule (H₂O), the electrons shared between the oxygen and hydrogen atoms are localized, meaning they are confined to their respective bonds.

In ethane (C₂H₆), each carbon atom is bonded to hydrogen atoms with localized sigma bonds.

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3. Delocalized Bond

A delocalized bond is a type of bond where the bonding electrons are not confined to two atoms but are spread over several atoms. This often happens in molecules with conjugated systems or resonance structures, where electrons are shared over multiple atoms, forming a "cloud" of electrons that provides stability to the molecule.

Example: In a benzene molecule (C₆H₆), the electrons forming the π bonds are delocalized across all six carbon atoms in the ring, contributing to the molecule's stability and unique chemical properties.

4. Delocalized Electrons

Delocalized electrons are electrons that are not associated with a single atom or a single covalent bond. Instead, they are spread across multiple atoms, allowing for electron mobility and contributing to properties like electrical conductivity and enhanced stability in molecules.

Example: In metals, electrons are delocalized throughout the structure, allowing metals to conduct electricity efficiently. Similarly, in conjugated molecules like benzene, the π electrons are delocalized across the entire ring structure.

Key Differences Between Localized and Delocalized Bonds

Aspect	Localized Bond	Delocalized Bond
Definition:	A covalent bond where the electron density is primarily concentrated between two bonded atoms.	A bond in which electron density is spread over multiple atoms or a larger region, rather than being confined to two atoms.
Type of Molecules	Found in simple molecules (e.g., ethane, H₂, Cl₂).	Found in conjugated systems (e.g., benzene, graphite).
Electron Position:	Electrons are confined to a specific region between the two atoms, forming a distinct bond.	Electrons are not confined to a specific region between two atoms but spread over multiple atoms or regions.
Occurrence:	Typically found in covalent compounds where electrons are shared between two atoms.	Commonly found in molecules with extended pi systems or resonance structures.
Electron Behavior:	Electrons are associated with specific atom pairs and are not free to move throughout the molecule.	Electrons are shared among multiple atoms or regions, rather than being associated with specific atom pairs.
Bond Length:	Has a well-defined bond length determined by the distance between the two atoms.	May not have a specific bond length since the electrons are distributed over a larger area.