Question

A solid is very hard and has a high melting point. Neither the solid nor its melt conducts electricity. Classify the solid.

Short answer

The solid is a covalent network solid.

Step-by-step solution

Understanding the Properties

Identify the given properties of the solid. The solid is described as very hard, has a high melting point, and neither the solid nor its melt conducts electricity.

Evaluating Conductivity

Evaluate the information that neither the solid nor its melt conducts electricity. This property is characteristic of some covalent crystals (like diamond) and some ionic solids in their solid form.

Considering Hardness and Melting Point

Consider the high hardness and melting point. Such properties are common to covalent network solids, which are held together by strong covalent bonds throughout the entire structure.

Final Classification

Based on the characteristics of being very hard, having a high melting point, and not conducting electricity, classify the solid as a covalent network solid. These properties match those of solids like diamond or silica.

Key concepts

Electrical Conductivity

When considering the ability of a substance to conduct electricity, it's all about the movement of charged particles. For a solid to conduct electricity, it should allow electrons or ions to move freely. Metals and ionic solutions, for example, typically conduct well because they have delocalized electrons or mobile ions. However, covalent network solids, like diamond, do not conduct electricity. This is because their electrons are tightly bound within the strong covalent bonds, leaving no free electrons to move around. So, if a solid and its melt do not conduct electricity, it's often an indication of a covalent network solid.

Hardness

Hardness is a measure of a material's resistance to deformation. Covalent network solids are known for their impressive hardness. This characteristic arises due to the vast, complex network of covalent bonds that hold their atoms in a rigid structure. These strong, directional bonds provide great resistance to being pushed apart or deformed. Diamond is a prime example, ranking as the hardest natural material thanks to its continuous three-dimensional network of carbon atoms connected by covalent bonds.

Melting Point

The melting point of a material gives insight into the strength of interaction between its constituent particles. For covalent network solids, the melting point is typically very high. Such a high melting point is attributed to the extensive network of covalent bonds. Breaking a covalent network requires a significant amount of energy because you need to overcome these strong bonds throughout the entire structure. Therefore, materials like diamond and silica have high melting points due to their robust covalent bonding.

Covalent Bonds

Covalent bonds are formed when two atoms share electrons to achieve stability. In covalent network solids, these bonds form a continuous network that extends throughout the material. The strength and stability of covalent bonds contribute to many properties of these solids, including hardness and high melting points. Unlike in simpler covalent compounds, these solids involve an extensive set of covalent bonds that make the material highly cohesive. This network bonding not only enhances strength and stability but also restricts electrical conductivity, as the electrons are not free to move around.