Question

Hypothesize What type of crystalline solid do you predict would best suit the following needs? a. a material that can be melted and reformed at a low temperature b. a material that can be drawn into long, thin wires c. a material that conducts electricity when molten d. an extremely hard material that is nonconductive

Short answer

a. A molecular crystalline solid would best suit the need for a material that can be melted and reformed at a low temperature. b. A metallic crystalline solid would best suit the need for a material that can be drawn into long, thin wires. c. An ionic crystalline solid would best suit the need for a material that conducts electricity when molten. d. A covalent network crystalline solid would best suit the need for an extremely hard material that is nonconductive.

Step-by-step solution

a. Material that can be melted and reformed at a low temperature

The material required must possess a low melting point. Among all types, molecular solids have low melting points due to intermolecular forces being weaker than metallic, ionic, or covalent bonds. Therefore, a molecular crystalline solid would best suit this need.

b. Material that can be drawn into long, thin wires

Materials that can be drawn into long, thin wires need to be ductile and malleable. Metallic crystalline solids have high ductility and malleability due to the mobility of their valence electrons. Therefore, a metallic crystalline solid would best suit this need.

c. Material that conducts electricity when molten

In order for a material to conduct electricity when molten, it needs to have charged particles that can move freely. Ionic solids have charged particles, i.e., ions, which can move freely in the molten state and thus conduct electricity. Therefore, an ionic crystalline solid would best suit this need.

d. Extremely hard material that is nonconductive

The material needed must be hard and non-conductive. Covalent network solids possess strong covalent bonds within the structure and do not have free electronic charge carriers. This makes them hard and non-conductive. Therefore, a covalent network crystalline solid would best suit this need.

Key concepts

Molecular Solids

Molecular solids are composed of atoms or molecules held together by intermolecular forces, rather than by actual chemical bonds. These forces include hydrogen bonds, van der Waals forces, and dipole-dipole interactions. Due to these relatively weak forces, molecular solids typically have low melting points, which makes them suitable for applications where materials need to be melted and reformed easily.

Some examples of molecular solids include ice, dry ice (solid \(CO_2\)), and sulfur. These solids are often soft, have low density, and are fairly poor conductors of electricity. This softness and low melting point attribute arise because breaking intermolecular attractions requires less energy compared to breaking ionic or covalent bonds.

In summary, molecular solids are ideal for applications that require low melting temperatures and easy reshaping, though they are limited by their mechanical strength and thermal conductivity.

Metallic Solids

Metallic solids consist of metal atoms arranged in a grid-like structure. The fascinating property of metallic solids lies in the sea of electrons that are free to move throughout the structure. This electron mobility is responsible for many of their remarkable characteristics.

Key attributes of metallic solids include high electrical and thermal conductivity, malleability, and ductility. Malleability allows metals to be hammered into thin sheets, while ductility enables them to be drawn into wires. Examples include aluminum, copper, and iron, which are widely used in everything from electrical wiring to construction due to these properties.

• High electrical conductivity
• Ability to withstand deformation (malleability and ductility)
• Shiny surface due to electron interaction with light

The free-moving electrons contribute to their strength and ability to conduct electricity, ensuring metallic solids remain indispensable in industrial and household applications.

Ionic Solids

Ionic solids are formed by the electrostatic attraction between positively and negatively charged ions. These solids have a crystalline structure resulting from the repeating patterns of ions.

An important feature of ionic solids is their electrical conductivity when they are molten or dissolved in water. This occurs because the ions are free to move and carry charge when not in the fixed solid state. At room temperature, however, ionic solids do not conduct electricity.

Common examples of ionic solids include table salt (\(NaCl\)) and other metal halides. They tend to have high melting points due to the strong attractions between charged ions and are often hard and brittle.

Ionic solids are ideal for applications that require materials to conduct electricity in a molten state but remain solid under normal conditions, providing excellent thermal stability.

Covalent Network Solids

Covalent network solids are one of the hardest materials known due to their structure. They are composed of atoms connected by an extensive network of covalent bonds. This bonding can span the entire solid, resulting in a very stable, rigid structure.

These solids are non-conductive because all electrons are tied up in the lattice and unavailable to move freely. Some well-known examples include diamond and quartz. Diamond, for instance, is renowned for its unrivaled hardness and clarity. Quartz consists of silicon dioxide molecules linked in a rigid framework.

The significant strength of covalent network solids makes them suitable for high-durability applications, such as cutting tools or abrasive surfaces. Despite their hardness, they are generally poor conductors of both heat and electricity.

Properties of Crystalline Solids

Crystalline solids are characterized by an orderly arrangement of their constituent particles, whether atoms, ions, or molecules, forming a well-defined repeating pattern.

This structured arrangement contributes to their distinct properties, including defined melting points and predictable mechanical strengths. These properties differ based on the type of bonding and particle arrangement within the crystal lattice.

• Clearly defined geometric shapes
• Sharp melting points
• Variety in electrical properties, from insulators to conductors

Recognizing the type of crystalline solid—be it molecular, metallic, ionic, or covalent network—allows us to predict how the material will behave in different situations. This understanding is crucial in fields like material science and engineering, where selecting the right material with the needed properties can influence the success of a project.