Problem 41 - Chemistry: Principles and Reactions

Question

Of the four general types of solids, which one(s) (a) are generally low-boiling? (b) are ductile and malleable? (c) are generally soluble in nonpolar solvents?

Step-by-Step Solution

Answer

Provide examples for each property. Answer: (a) Molecular solids typically exhibit low boiling points due to the weak intermolecular forces between their molecules, such as in sugar, ice, and dry ice (solid CO2). (b) Metallic solids, such as gold, silver, and copper, are ductile and malleable due to their metallic bonds and the "sea" of delocalized electrons surrounding the metal atoms. (c) Nonpolar molecular solids, like iodine (I2) and fullerenes (e.g., C60), are soluble in nonpolar solvents (e.g., hexane or benzene) because their weak London dispersion forces get disrupted by other nonpolar molecules.

Step 1: (a) Low-Boiling Solids:

Low-boiling solids are those that transition from the solid phase to the gaseous phase at relatively low temperatures. In the context of the four general types of solids, molecular solids typically exhibit low boiling points. Molecular solids consist of weak intermolecular forces (like van der Waals forces and hydrogen bonds) between their molecules, which require less energy to break. Examples of molecular solids include sugar, ice, and dry ice (solid CO2).

Step 2: (b) Ductile and Malleable Solids:

Ductile and malleable solids are those that can be stretched or deformed without breaking or cracking. In the context of the four general types of solids, metallic solids are ductile and malleable. Metallic bonds consist of metal atoms surrounded by a "sea" of delocalized electrons that contribute to their ability to hold their structure even when significant stress is applied. Examples of ductile and malleable solids include gold, silver, and copper.

Step 3: (c) Soluble in Nonpolar Solvents:

Solids that are soluble in nonpolar solvents generally have a similar nature as nonpolar solvents; that is, they exhibit low polarity or no polarity at all. Within the four types of solids, molecular solids (with nonpolar molecules) demonstrate solubility in nonpolar solvents. Furthermore, nonpolar molecular solids are held together by weak London dispersion forces, which get disrupted by other nonpolar molecules. Examples of nonpolar molecular solids include iodine (I2) and fullerenes (like C60), which are soluble in nonpolar solvents like hexane or benzene.

Key Concepts

Molecular Solids

Molecular solids are composed of molecules held together by relatively weak intermolecular forces. These forces can include van der Waals forces and hydrogen bonds.
Due to these weaker forces, molecular solids typically have lower melting and boiling points compared to other types of solids. This means they can transition from a solid to a liquid or gas at relatively low temperatures.

• Examples of molecular solids include ice (solid water), dry ice (solid CO2), and sucrose (sugar).
• These solids are also known for being poor conductors of electricity, as they lack free-moving charged particles.

In environments where pressures and temperatures are low, molecular solids like ice can sublimate, directly moving from solid to gas.

Metallic Solids

Metallic solids are known for their distinctive metallic bonding, where positive metal ions are surrounded by a sea of delocalized electrons.
This electron sea allows metallic solids to be excellent conductors of electricity and heat, as these electrons can move freely through the lattice.

• One of the hallmark traits of metallic solids is their ductility and malleability. They can be drawn into wires or hammered into thin sheets without breaking.
• Metals like copper, aluminum, and gold exemplify these properties and are used extensively in industrial applications for these reasons.

The strength and durability of metallic solids also make them essential in construction and manufacturing.

Solubility in Nonpolar Solvents

Solubility is a measure of how well a substance can dissolve in a solvent. When it comes to nonpolar solvents, nonpolar solids tend to dissolve better.
Molecular solids that have nonpolar molecules will generally dissolve in nonpolar solvents due to the similar nature of their intermolecular forces.

• Common nonpolar solvents include hexane and benzene, which are often used to dissolve nonpolar molecular solids such as iodine and fullerenes.
• In nonpolar solutions, the disruption of weak dispersion forces among molecules allows for dissolution.

This principle is an example of "like dissolves like," which is a fundamental concept in chemistry regarding solubility.

Boiling Points of Solids

The boiling point of a solid generally depends on the strength of the forces holding its particles together.
Solids with weak intermolecular forces, like molecular solids, have lower boiling points because less energy is needed to break these interactions.

• Molecular solids, such as CO2 in its solid form (dry ice), can change to gas at temperatures as low as -78.5°C under atmospheric pressure.
• In contrast, ionic and covalent solids, with much stronger bonds, require higher temperatures to vaporize.

Understanding the boiling points of different solids can help predict their behavior and potential applications in various conditions.