Question

Boron reacts with nitrogen at higher temperatures and pressures forming boron nitride. It is (1) a slippery whitc solid with a layer structure similar to graphitc. (2) a whitc solid with diamond-like structure. (3) a liquid and is structurally similar to silicon dioxidc. (4) a liquid and is isostructural with benzenc.

Short answer

Option 2: a white solid with diamond-like structure.

Step-by-step solution

Understand the given information

Boron reacts with nitrogen at high temperatures and pressures to form boron nitride. The task is to determine the correct physical and structural properties of boron nitride from the given options.

Analyzing the properties

Consider the common forms of boron nitride. There are primarily two forms based on different structures: hexagonal boron nitride (h-BN), which is similar to graphite and is known for being slippery, and cubic boron nitride (c-BN), which has a diamond-like structure.

Matching with the provided options

Evaluate each option to see which aligns with the known properties of boron nitride. 1. A slippery white solid with a layer structure similar to graphite. This matches hexagonal boron nitride (h-BN). 2. A white solid with diamond-like structure. This matches cubic boron nitride (c-BN). 3. A liquid and structurally similar to silicon dioxide. Boron nitride is not liquid and this description doesn't match.4. A liquid and is isostructural with benzene. Again, boron nitride is not liquid.

Choosing the correct answer

Based on the analysis, boron nitride can be either a slippery white solid with a layer structure similar to graphite (option 1) or a white solid with a diamond-like structure (option 2). However, the prevalent form of boron nitride under the conditions given (high temperature and pressure) is typically cubic boron nitride (c-BN).

Key concepts

Hexagonal Boron Nitride

Hexagonal boron nitride (h-BN) is one of the most well-known forms of boron nitride. It is similar in structure to graphite, which means it consists of layers that can easily slide over one another. This gives h-BN its characteristic slippery feel. Here are some key properties of hexagonal boron nitride:

• Appearance: It is a white, non-toxic solid.
• Structure: The layers are made up of hexagons of boron and nitrogen atoms, aligned in a honeycomb pattern.
• Lubricant: Due to its slippery nature, h-BN is often used as a lubricant in various industrial applications.
• Heat resistance: It can withstand high temperatures, making it useful in high-temperature environments.

The similarity to graphite means that h-BN can be used in applications where lubrication at high temperatures is required. This form of boron nitride is also an excellent electrical insulator, while still conducting heat, making it a unique material for thermal management in electronics.

Cubic Boron Nitride

Cubic boron nitride (c-BN) is another important form of boron nitride, distinct from h-BN. It has a structure similar to that of diamond, which gives it remarkable properties. Here are some details about cubic boron nitride:

• Appearance: It is a white, crystalline solid.
• Structure: The atoms are arranged in a cubic crystal lattice, like diamond.
• Hardness: c-BN is extremely hard, second only to diamond. This makes it a valuable material for industrial cutting and grinding tools.
• Thermal and chemical stability: It remains stable at high temperatures and in harsh chemical environments, where diamond would decompose or react.

These properties make c-BN an excellent material for applications requiring high durability and stability. It is often used in the manufacturing of cutting tools, abrasive wheels, and other materials that must maintain their properties under extreme conditions.

Structures of Boron Nitride

Boron nitride (BN) can exist in different structural forms, each with unique properties. The two most common structures are hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN).

In h-BN, the atoms are arranged in a hexagonal pattern forming layers, similar to graphite. This structure allows the layers to slide over each other, giving h-BN its lubricating property. On the other hand, c-BN has a cubic crystal lattice, resembling the structure of diamond. This gives c-BN its exceptional hardness and stability.

Depending on the synthesis conditions, boron nitride can transition between these structures. For instance:

• High temperature and pressure favor the formation of cubic boron nitride (c-BN).
• Lower temperatures and regular atmospheric pressure commonly result in hexagonal boron nitride (h-BN).

Understanding these structures is crucial in selecting the right type of boron nitride for specific applications, whether it’s for lubrication, thermal management, or high-durability tools.