Question

Which of the following statement is correct for graphite? (1) Its layers are very tightly packed, almost withou tany space between them. (2) It cleaves easily between the layers which acounts for the remarkable softness of the crystals. (3) Its density is lower than that of diamond (4) It has a layered structure and the bonding between the layers is very weak. (a) 2,4 (b) \(1,2,4\) (c) \(1,2,3\) (d) \(2,3,4\)

Short answer

The correct combination is (d) 2,3,4.

Step-by-step solution

Analyze Statement 1

Statement (1) claims that graphite's layers are very tightly packed, almost without any space between them. This is incorrect because graphite's layers are separated by weak van der Waals forces, providing space between them and allowing the layers to slide over each other.

Analyze Statement 2

Statement (2) suggests it cleaves easily between the layers, which accounts for the remarkable softness of the crystals. This statement is correct because graphite is composed of layers that can easily slide over one another.

Analyze Statement 3

Statement (3) claims that the density of graphite is lower than that of diamond. This is correct because diamond has a very dense and tightly packed structure, whereas graphite's layered structure allows for a lower density.

Analyze Statement 4

Statement (4) claims that graphite has a layered structure and the bonding between the layers is very weak. This is correct, as the layers in graphite are held together by weak van der Waals forces, allowing them to slide.

Determine the Correct Combination

From the analysis: statements (2), (3), and (4) are correct. Therefore, the correct combination of statements is found in option (d) 2,3,4.

Key concepts

Van der Waals Forces

In graphite, the atoms within each layer are strongly bonded through covalent bonds, but the layers themselves are connected by weak interactions known as van der Waals forces.
These forces are responsible for the distinct behavior of graphite compared to other carbon allotropes, such as diamond.

• Van der Waals forces allow the layers in graphite to remain parallel yet loosely attached, making them easy to separate.
• This weak bonding not only provides graphite with its unique slipperiness but also makes it an excellent lubricant.

In essence, these forces play a crucial role in defining many of graphite’s properties, including its electrical conductivity and its ability to cleave easily between layers. This is why when you write with a pencil, the graphite leaves marks on the paper: the layers can slide off onto surfaces effortlessly.

Layered Structure

Graphite's layered structure is key to its many unique properties. In each layer, carbon atoms are arranged in a hexagonal lattice, forming strong covalent bonds with their neighbors.
This architecture provides high strength within the layer. However, it's the arrangement of these layers that makes graphite particularly intriguing.

• The layering allows the material to show flexibility and bendability along the planes.
• Since the forces between the layers (van der Waals forces) are weak, layers can slide over one another, contributing to graphite's softness.

This structural feature also plays a part in graphite's ability to conduct electricity, which is mostly possible within the layers. This distinct structure underlies graphite's dual nature of being both robust in two dimensions within a single layer and malleable in three dimensions due to the sliding layers.

Density Comparison with Diamond

Graphite and diamond, although both made of carbon atoms, exhibit notably different densities due to their structural differences.
The density of a material is fundamentally dependent on the packing of its atoms.

• Graphite's layered structure means that there are gaps between the layers due to the weak van der Waals forces holding them together.
• Diamond, on the other hand, has a tightly packed lattice structure where each carbon atom is covalently bonded to four others, resulting in no gaps.

Thus, diamond tends to have a higher density in comparison to graphite. This higher density contributes to diamond's reputation as one of the hardest known substances, while graphite's lower density allows it to be soft and easily used in applications like writing and lubrication.