Graphite, an allotrope of carbon, is an example of which type of crystalline solid based on its bonding and structure?

Introduction / Context:
Different solids are classified according to the nature of the forces that hold their atoms or molecules together. Graphite, an allotrope of carbon, has a unique structure that gives it special properties like good electrical conductivity along layers and easy cleavage. This question tests your knowledge of the type of crystalline solid graphite represents.

Given Data / Assumptions:
- The substance is graphite, an allotrope of carbon.- We are to classify it as metallic, ionic, molecular, or covalent network.- Standard high school solid state chemistry descriptions apply.

Concept / Approach:
Graphite consists of layers of carbon atoms arranged in hexagonal rings. Within each layer, atoms are bonded strongly by covalent bonds, forming extended two dimensional networks. Between layers, only weak forces act, allowing layers to slide. This structure is characteristic of a covalent network solid, where atoms are linked by covalent bonds in a continuous network. Diamond, another carbon allotrope, is also a covalent network solid, but its network is three dimensional.

Step-by-Step Solution:
1. Recall that metallic crystals have positive metal ions immersed in a sea of mobile electrons, as in sodium or copper.2. Ionic crystals are formed by ions held together by electrostatic forces, as in sodium chloride.3. Molecular crystals consist of discrete molecules held by weak intermolecular forces, as in dry ice or iodine crystals.4. Covalent network crystals consist of atoms bonded covalently in a continuous network extending throughout the crystal.5. Since graphite has covalently bonded carbon atoms forming extended sheets, it fits the covalent network category.

Verification / Alternative check:
Textbooks often list graphite and diamond together as typical covalent network solids. Graphite being an electrical conductor is sometimes mistaken for a metallic solid, but its bonding is still covalent, not metallic. The directional covalent bonds within layers and the large melting point support classification as a covalent network solid rather than a molecular solid.

Why Other Options Are Wrong:
- Metallic crystal: Graphite conducts electricity but lacks a lattice of metal cations with delocalised valence electrons; its basic building units are neutral carbon atoms bonded covalently.- Ionic crystal: There are no separate positive and negative ions; graphite consists only of carbon atoms.- Molecular crystal: Graphite does not consist of separate molecules; it has infinite covalent layers, so it is not molecular.

Common Pitfalls:
Because graphite conducts electricity, students sometimes misclassify it as metallic. Remember that conduction can arise from delocalised electrons in covalent networks as well. The key is the nature of bonding: extended covalent bonding indicates a covalent network crystal. Metallic crystals always involve metallic elements with characteristic metallic bonding.

Final Answer:
Graphite is an example of a covalent-network crystalline solid.