Question

Which of the following has hexagonal structure? (a) diamond (b) sodium chloride (c) graphite (d) both (a) and (c)

Short answer

Graphite has a hexagonal structure.

Step-by-step solution

Understand Crystal Structures

Begin by understanding what a hexagonal structure is. Hexagonal structures are arrangements of atoms in a crystalline formation characterized by six-sided symmetry. In a hexagonal lattice, each layer is stacked over two others to minimize voids within the structure.

Analyze Diamond Structure

Diamond has a crystal structure that consists of a cubic arrangement of carbon atoms. This is known as a face-centered cubic or diamond cubic structure, which is not hexagonal. Each carbon atom forms four covalent bonds in a tetrahedral configuration.

Analyze Sodium Chloride Structure

Sodium chloride (NaCl) crystallizes in a cubic lattice, specifically a face-centered cubic structure. This arrangement is characteristic of ionic crystals and is also not hexagonal. The ions are alternately stacked in a repeating cubic pattern.

Analyze Graphite Structure

Graphite, unlike diamond, has a hexagonal crystal structure. In graphite, layers of carbon atoms are arranged in a hexagonal grid. Each carbon atom is bonded to three others within the same layer, forming flat sheets of hexagons, and the layers are loosely held together by Van der Waals forces.

Conclusion Based on Analysis

After analyzing each option, it's evident that graphite has a hexagonal structure. Diamond and sodium chloride do not fit this criterion. Thus, among the given options, only graphite aligns with the hexagonal structure description.

Key concepts

Hexagonal Structure

Hexagonal structures in crystals are fascinating arrangements where atoms align in a six-sided symmetry. This type of structural formation includes a series of planes that are stacked in a specific repeating pattern. These layers are typically arranged in a way that minimizes the empty spaces, or voids, between atoms. This efficient packing often results in the hexagonal closest packed (HCP) configuration. Such arrangements allow for a highly stable and strong form, making hexagonal structures prevalent in materials with significant durability and resilience. Some metals, like magnesium and zinc, naturally form hexagonal lattices, illustrating the variety of elements that can adopt this structure.

Diamond Structure

In diamond, each carbon atom is covalently bonded to four other carbon atoms, forming a rigid three-dimensional network. This structure is known as a face-centered cubic lattice, specifically a diamond cubic structure. This organization provides diamonds their renowned hardness and brilliant shine. The tetrahedral arrangement allows for strong covalent bonding, resulting in a material that can cut through many other substances. Diamonds' structure is not hexagonal. Instead, the intricate cubic arrangement sets it apart from graphite, which is also made entirely of carbon, yet has a vastly different structure and properties.

Graphite Structure

Graphite stands out with its unique hexagonal structure. In graphite, carbon atoms are bonded together in flat sheets within layers, resembling a honeycomb pattern. Each carbon atom forms three covalent bonds with neighboring atoms in the same layer. This creates a planar hexagonal network. These layers of hexagonal networks, however, are only weakly held together by Van der Waals forces. This weak interlayer bonding allows layers to slide over each other easily, which is why graphite is an excellent lubricant and is used in pencils for writing. Unlike diamond, graphite's structure makes it soft and easy to break apart.

Sodium Chloride Structure

The structure of sodium chloride, commonly known as salt, is quite different from hexagonal or even carbon-based lattices. NaCl has a face-centered cubic structure, typical of ionic crystals. In sodium chloride, each sodium ion \(Na^+\) is surrounded by six chloride ions \(Cl^-\), and vice versa. This alternating stack of positive and negative ions forms a repeating cubic pattern. The electrostatic attraction between oppositely charged ions provides sodium chloride its stability and high melting point. This robust ionic bonding differs significantly from the covalent bonds found in carbon-based structures like diamond and graphite.