Amorphous Solids – Class 12 | Chapter – 1 | Chemistry Short Notes Series PDF for NEET & JEE
Amorphous Solids: Amorphous solids are materials that lack a long-range ordered arrangement of atoms or molecules, unlike crystalline solids. In amorphous solids, the atoms or molecules are arranged randomly, and the material lacks a definite geometric shape. Some examples of amorphous solids include glass, rubber, and plastics. Amorphous solids can be formed in several ways, such as by rapidly cooling a molten material or by depositing atoms or molecules onto a substrate at low temperatures. The lack of a long-range order in amorphous solids makes them difficult to study, but various experimental techniques, such as X-ray diffraction and transmission electron microscopy, can be used to analyze their structure and properties.
Types of Amorphous Solids
There are several types of amorphous solids, each with their unique properties and characteristics. Here are a few examples:
- Glass: Glass is one of the most common types of amorphous solids. It is made by cooling a molten material, such as silica, quickly, preventing the atoms or molecules from forming a crystalline structure. Glass is transparent, brittle, and has a high electrical resistance.
- Rubber: Rubber is an elastic amorphous solid that is made from natural or synthetic polymers. It is highly flexible and can be stretched and deformed without breaking. Rubber has many industrial and commercial applications, such as in the production of tires, hoses, and gaskets.
- Plastics: Plastics are synthetic amorphous solids made from a wide range of organic polymers. They are lightweight, durable, and can be molded into various shapes and sizes. Plastics have a wide range of applications, from food packaging to car parts.
- Gels: Gels are a type of amorphous solid that contains a liquid component. They are formed by mixing a liquid with a solidifying agent, such as agar or gelatin. Gels are soft and can be deformed, but they retain their shape due to the solidifying agent.
- Amorphous metals: Amorphous metals, also known as metallic glasses, are a relatively new class of amorphous solids. They are made by cooling a molten metal at a high rate, preventing the atoms from forming a crystalline structure. Amorphous metals have unique mechanical, magnetic, and electrical properties and are used in a wide range of applications, such as in electrical transformers and biomedical implants.
Properties of Amorphous Solids
Amorphous solids have a unique set of properties that distinguish them from crystalline solids. Here are some of the main properties of amorphous solids:
- Lack of long-range order: Unlike crystalline solids, amorphous solids lack a long-range ordered arrangement of atoms or molecules. This means that their atomic structure is random and disordered.
- Isotropic properties: Amorphous solids exhibit isotropic properties, meaning their properties are the same in all directions. In contrast, crystalline solids have anisotropic properties, meaning their properties vary depending on the direction.
- Gradual softening and flow: Amorphous solids do not have a well-defined melting point like crystalline solids. Instead, they gradually soften and flow when heated, which is known as the glass transition.
- Brittle: Amorphous solids are typically brittle and prone to fracture when subjected to stress or strain. This is because their atomic structure lacks the regular arrangement found in crystalline solids, which makes them more susceptible to fracture.
- Low density: Amorphous solids tend to have lower densities than crystalline solids. This is because their random atomic structure allows for more empty space between atoms or molecules.
- High thermal expansion coefficient: Amorphous solids have a higher thermal expansion coefficient than crystalline solids. This means that they expand more when heated and contract more when cooled.
- Transparent: Some amorphous solids, such as glass, are transparent and allow light to pass through them.
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