Problem 134 - A Complete Resource Book in Chemistry for JEE Main

Question

Graphite is a (a) Good conductor of electricity (b) Good insulator (c) Bad conductor of heat (d) Good conductor of heat

Step-by-Step Solution

Answer

Graphite is a good conductor of electricity and heat (a and d).

Step 1: Understanding the Properties of Graphite

Graphite is a form of carbon where the atoms are arranged in layers. These layers can slide over one another, which contributes to its unique properties.

Step 2: Electrical Conductivity

Graphite is known for being a good conductor of electricity due to the presence of free electrons that can move between the layers. When a voltage is applied, these electrons can flow, thus conducting electricity.

Step 3: Thermal Conductivity

Graphite is also known to be a good conductor of heat. The delocalized electrons that help in electrical conductivity also facilitate thermal conductivity, allowing heat to be transferred efficiently along the graphite structure.

Step 4: Eliminating Incorrect Options

From the properties examined, we can eliminate option (b) 'Good insulator' and option (c) 'Bad conductor of heat'. This is because graphite conducts both electricity and heat well.

Key Concepts

Electrical Conductivity

Graphite's electrical conductivity is one of its most fascinating properties. This ability to conduct electricity stems from its structure. Carbon atoms in graphite are arranged in layers, and within these layers, each carbon atom is bonded to three others, leaving one free electron per atom. These free-moving electrons are called delocalized electrons.
They can move across the layers, almost like a "sea" of electrons. When you apply a voltage, these electrons are able to flow freely between the layers, conducting electricity effectively.

• Free electrons are crucial for electrical conduction.
• Voltage application helps these electrons move and carry current.

This makes graphite an excellent conductor of electricity, unlike traditional insulators that have all electrons tightly bound to atoms. Remember, insulators prevent electricity flow because they lack free electrons.

Thermal Conductivity

Graphite's layers not only facilitate electrical conductivity but also enable efficient heat transfer. Thermal conductivity is the measure of how well a material can conduct heat. Like copper or aluminum, graphite is an excellent conductor of heat due to the same free, delocalized electrons responsible for conducting electricity.
These electrons can rapidly transfer thermal energy through the material.
This means that if one part of graphite is heated, the heat can quickly spread throughout the material.

• Delocalized electrons play a dual role—conducting both electricity and heat.
• High thermal conductivity implies efficient heat dispersion.

In practical uses, graphite is employed in heat sinks and electrical components to manage heat efficiently, ensuring that devices don't overheat during operation.

Graphite Structure

The unique structure of graphite is central to its distinctive properties. Graphite is a crystalline allotrope of carbon, where the carbon atoms are arranged in a hexagonal pattern. These patterns form layers known as graphene layers.
Here's how the structure works: Each carbon atom is bonded with three others in a plane, creating incredibly strong covalent bonds within the layers. However, the forces between the individual layers are relatively weak Van der Waals forces. This means layers can slide over one another quite easily, which is why graphite feels slippery. This slip property is what makes graphite useful as a lubricant.

• Each atom is held in a robust hexagonal sheet within its layer.
• Weak forces between layers account for graphite being used in pencils as it allows layers to easily flake off.

Overall, the ability to slide layers contributes to many of graphite’s uses, from writing materials to industrial applications like brake linings and lubricants.