Question

In graphite, electrons are (1) localized on each carbon (2) delocalized along the layers (3) localized on every third carbon (4) present in anti-bonding orbital

Short answer

Electrons in graphite are delocalized along the layers (option 2).

Step-by-step solution

Understand Graphite Structure

Graphite consists of layers of carbon atoms arranged in a hexagonal lattice. Each carbon atom is bonded to three other carbon atoms within the same layer, forming a planar structure.

Delocalized Electrons Concept

In graphite, each carbon atom forms three sigma bonds using three of its four valence electrons. The fourth electron is free to move within the layer, contributing to a 'sea of electrons'.

Electrons Between Layers

These free-moving electrons (delocalized electrons) can move along the layers but not between them, as the layers are bonded by weak van der Waals forces.

Correct Option Identification

Based on the understanding of graphite, the free electrons are delocalized along the layers. Thus, the correct answer is option (2).

Key concepts

Delocalized Electrons

In graphite, the concept of delocalized electrons is crucial for understanding its electrical and thermal properties. Each carbon atom in graphite is bonded to three other carbon atoms through sigma bonds, using three of its four valence electrons. The fourth electron, however, does not participate in the sigma bonding.

This fourth electron is free to move within the layer of the graphite structure. Because these electrons are not bound to any specific carbon atom, they are referred to as delocalized electrons. This 'sea of electrons' can move freely across the plane of the graphite layer, allowing for the conduction of electricity.

Delocalized electrons contribute to the overall stability of the graphite structure and give it its characteristic metallic sheen. These free-moving electrons also play a role in the material's ability to conduct heat, making graphite an excellent conductor.

Graphite Structure

Graphite has a unique structure that is foundational to its properties. It consists of layers upon layers of carbon atoms arranged in a hexagonal lattice. Each carbon atom within a layer forms three covalent bonds with three other carbon atoms, creating a planar and stable structure.

These layers stack on top of each other to form the bulk material of graphite. The bonding within each layer is strong because of the covalent bonds, making each layer highly stable and resilient.

However, the bonding between the layers is much weaker. The layers are held together by van der Waals forces, which are relatively weak intermolecular forces. This weak interlayer bonding allows the layers to slide over each other easily, contributing to graphite's lubricative properties and its use in products like pencil leads and lubricants.

Van der Waals Forces

In graphite, the layers are held together by weak non-covalent interlayer forces known as van der Waals forces. These forces are significantly weaker than the covalent bonds within each graphite layer.
Van der Waals forces arise from temporary dipoles that occur when the electron distribution within a molecule or material becomes asymmetrical. This creates a slight attraction between adjacent layers of graphite.

The result is a structure where the layers can easily slide over one another. This property enables graphite to act as a good lubricant and make it easy to write with pencils, as the layers shear off and deposit onto paper.

Despite their weakness, van der Waals forces are essential for maintaining the layered structure of graphite. Without them, the layers would not stay together, and the material would not exhibit its unique physical properties.