Question

A solid is hard, brittle, and electrically nonconducting. Its melt (the liquid form of the substance) and an aqueous solution containing the substance conduct electricity. Classify the solid.

Short answer

The solid is classified as an ionic solid.

Step-by-step solution

Identify Characteristics

First, let's identify the key characteristics provided in the exercise: The solid is hard, brittle, and electrically nonconducting in its solid state. However, when melted or dissolved in water, it conducts electricity.

Analyze Electrical Conductivity

The fact that the solid does not conduct electricity in its solid form but does in its molten and aqueous forms suggests that there are no free-moving electrons initially, but such charges become available when the solid is melted or dissolved.

Compare with Known Types of Solids

Based on its properties, this solid should be compared with known solids: 1. **Metallic solids** are conductive in solid form. 2. **Molecular solids** are generally nonconductive in all states. 3. **Covalent network solids** generally do not conduct electricity. 4. **Ionic solids** do not conduct in solid form but conduct when melted or dissolved.

Classify the Solid

The properties fit those of an ionic solid, because ionic solids conduct electricity when melted or dissolved due to the movement of ions, even though they are nonconductive as solids.

Key concepts

Electrical Conductivity in Chemistry

Electrical conductivity refers to the ability of a substance to conduct electricity. This is closely tied to the movement of charged particles, such as electrons or ions. In metals, electrons move freely, which makes them excellent conductors. However, in ionic solids, the ions are locked in place, preventing the solid from conducting electricity in its solid state.

When an ionic solid is melted or dissolved in water, the rigid lattice structure breaks down. The ions become free to move, which allows for the flow of electric current. This transformation is key in understanding the electrical behavior of substances like salts, which need to be in a liquid state or dissolved for their conductive properties to become apparent.

• Solid State: Organizes ions in a fixed, rigid structure, preventing motion and conductivity.
• Melted or Dissolved: Breaks the lattice, freeing ions, and enabling electrical flow.

Properties of Solids in Chemistry

Different solids have distinct physical properties, defining their structure and utility. Let's explore these properties where factors like hardness, brittleness, and conductivity play significant roles.

Solids generally have a definite shape and volume. Their properties stem from the type of bonding and structure within the solid.

• **Hardness** refers to how resistant a solid is to shape changes under force. Ionic solids are often quite hard due to the strong ionic bonds in their crystalline lattice.
• **Brittleness** indicates that a solid is likely to break or shatter rather than deform under stress. This is common in ionic solids, where shifting layers can cause like-charged ions to repel each other.
• **Conductivity** in solids varies widely. Metals tend to show strong electrical conductivity, while ionic solids show none unless melted or dissolved.

Understanding these properties helps in the identification and classification of various types of solids.

Types of Solids in Chemistry

In chemistry, solids are classified into several categories based on their bonding and structural characteristics. Each type of solid has unique properties.

1. **Metallic Solids**: Characterized by a sea of delocalized electrons, allowing constant movement of charge, which makes them conductive both in solid and molten states. 2. **Molecular Solids**: Consist of molecules held together by intermolecular forces like van der Waals, dipole-dipole, or hydrogen bonds, usually resulting in poor conductivity. 3. **Covalent Network Solids**: Formed by atoms bonded in a continuous network throughout the solid. Examples include diamonds, and they generally do not conduct electricity. 4. **Ionic Solids**: Composed of ions held together by strong electrostatic forces in a lattice structure. These do not conduct electricity in solid form but do so when melted or dissolved because ions can then move freely.

• Metallic Solids: Good conductors, malleable, and ductile.
• Molecular Solids: Soft, low melting points, non-conductive.
• Covalent Network Solids: Hard, high melting points, usually non-conductive.
• Ionic Solids: Hard, brittle, electrically conductive when molten or in solution.