Problem 4 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a non-crystalline solids' pair? (a) diamond, wood (b) glass, table salt (c) wood, glass (d) sucrose, glass

Step-by-Step Solution

Answer

(c) wood, glass

Step 1: Understand Terms

Start by understanding what crystalline and non-crystalline solids are. Crystalline solids have a well-ordered, repeating arrangement of atoms, ions, or molecules, while non-crystalline (amorphous) solids do not have a definite inner structure.

Step 2: Identify Non-Crystalline Solids

Review the list of substances given: - Diamond is a crystalline solid. - Wood is amorphous (non-crystalline). - Glass is amorphous (non-crystalline). - Table Salt is a crystalline solid. - Sucrose is a crystalline solid.

Step 3: Evaluate Options

Go through each pair of substances given in the options: - (a) Diamond is crystalline, wood is non-crystalline. - (b) Glass is non-crystalline, table salt is crystalline. - (c) Wood is non-crystalline, glass is non-crystalline. - (d) Sucrose is crystalline, glass is non-crystalline.

Step 4: Choose the Correct Option

The only pair in which both substances are non-crystalline is option (c), where both wood and glass are amorphous solids.

Key Concepts

Crystalline solids

In the world of solid-state chemistry, crystalline solids are materials where the atoms, ions, or molecules are structured in an orderly, repeating pattern. This pattern extends throughout the entire solid, creating what is known as a crystal lattice. Due to their structured form, crystalline solids have definitive shapes and are often seen in geometrically perfect crystal forms. Characteristics of crystalline solids include:

• Sharp melting points, which mean they change from solid to liquid at a specific temperature.
• Mechanical rigidity and strength due to the strong bonds in their structures.
• Anisotropy, which means their physical properties can differ based on direction within the crystal.

Examples of crystalline solids include table salt ( 1 3 1 4), diamond, and sucrose. These solids are essential in many applications, from jewelry to everyday household items.

Amorphous solids

Amorphous solids, in contrast to crystalline ones, lack a well-defined, long-range order in the arrangement of their atoms or molecules. This results in a structure that is more random and uniform rather than ordered and periodic. Features of amorphous solids include:

• Lack of a sharp melting point. Instead, they soften over a range of temperatures.
• Isotropy, meaning their physical properties are the same in all directions due to their randomized structure.
• Lower mechanical strength when compared to crystalline solids.

Common examples of amorphous solids are glass and certain types of plastic. These materials are vital in various applications, such as in construction (e.g., glass windows) and in manufacturing (e.g., plastic containers), owing to qualities like transparency and moldability.

Glass structure

Glass is a fascinating example of an amorphous solid, primarily composed of silicon dioxide ( 1 2 2 3), among other components depending on the type of glass. The lack of a regular lattice in glass makes it non-crystalline and gives it unique properties. Some properties of glass include:

• Transparency, which allows it to transmit light, making it ideal for windows and lenses.
• Non-brittle nature compared to crystalline solids as it does not fracture along defined planes.
• Thermal stability up to certain temperatures, making it useful in a range of thermal applications.

Glass is produced by cooling molten materials so rapidly that they do not form a crystal structure. This creation process results in the random arrangement of molecules characteristic of amorphous solids, contributing to its characteristic look and feel.

Wood properties

Wood is a natural material that is classified as an amorphous solid. Unlike crystalline solids, wood has a more disorderly internal structure, which plays a key role in its unique properties. It is composed mainly of cellulose, hemicellulose, and lignin, with a substantial amount of water and air. Key properties of wood include:

• Elasticity and flexibility, allowing it to absorb shock and handle stress without permanent deformation.
• Anisotropy in its mechanical strength, as its properties vary along different grain directions.
• Porosity, owing to its cellular structure, which contributes to its insulating characteristics and weight efficiency.

Wood's natural beauty and renewable nature make it an eco-friendly material used in furniture, construction, and more. Its composition makes it less dense compared to metals, which lends itself well to being used in structures that require strong yet light support.