Chemistry Notes for Class 12 – Solid State | NCERT Solutions for class 12
In this article, we have discussed the about the solid state of matter, and the two different types of solids. It covers the Unit 1: Solid State, of CBSE Class 12th Chemistry.
Solid State – Chemistry Notes for Class 12
The matter is commonly encountered in one of three states— solid, liquid, or gas. Air is an example of a gas and water an example of a liquid. Objects such as rocks, concrete buildings, or pages in a book can be classified as solids. An analogy for the three states of matter is students in a classroom. The students sitting at their desks represent a solid state. Moving around the classroom, they are like a liquid. Once the bell rings, they are like a gas that is spread throughout the neighborhood. Now we can define solids as;
Solids are the chemical substances which are characterized by fixed shape and volume, rigidity, high density and low compressibility.
Solid state is the state of matter having fixed shape and volume, rigidity, high density and low compressibility.
Based on the arrangement of the particles, the solids are classified as;
- Amorphous solids
- Crystalline solids
Amorphous Solids: In condensed matter physics and materials science, an Amorphous (from the Greek a, without, morphé, shape, form) or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal.The solids which do not have any definite geometrical shape are called as amorphous solids. Glass is a classic example of an amorphous material.Glass is a heterogeneous material formed from silicon, oxygen, sodium, and a variety of other elements, depending upon the type of glass. It lacks long-range structure: Short units of silicon dioxide are bound together, but there is no overall order. At an atomic level, glass looks like a frozen liquid. Individual clusters exist, but they are not connected to each other and are held together only by van der Waals interactions. This is why when glass breaks it forms curved or jagged edges and why it shatters if struck with a hard blow. Another example is paper, composed of randomly oriented cellulose molecules. Many familiar objects are made up of amorphous solid materials, all lacking long-range structure or order. They are aperiodic substances—substances that do not display periodicity. Consequently, it is hard to analyze the structure of amorphous materials as each sample is unique. Some other examples of amorphous solids are rubber, plastic etc. Amorphous solids are isotropic i.e. the properties (like mechanical, thermal, electrical, optical) of isotropic materials are the same in all directions. In amorphous substances, the particles are randomly arranged and disordered. Due to this, all directions are equivalent and so all the properties remain the same in all directions.
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Crystalline solids: The solids which have a repetitive arrangement of atoms and molecules in a regular formation are known as crystalline solids. They have long-range order as these can extend for the massiveness of the structure. These solids have the low potential energy they are always considered as the most stable form of solids. Crystalline solids could be subdivided into either single or polyforms. The crystalline solids make up a much smaller percentage of everyday objects, but they are easier to understand. A sub-discipline of chemistry called crystallography is devoted to analyzing the crystalline material. Crystal displays long-range structure made up of the same building block used over and over.
In case of diamond, which is like glass in appearance, it is a covalent network solid with a three-dimensional lattice of tetrahedrally bound carbon atoms. Each carbon is attached to four neighbors in endless repetition. The three-dimensional structure and covalent bonds ensure that diamonds are incredibly hard. The critical feature of crystalline material is that it shows a periodicity of arrangement along with regularity. The crystalline substance is anisotropic i.e. its physical properties like mechanical, electrical, thermal and optical are different in different directions. For example, the velocity of light passing through crystal changes with the direction in which it is measured.
To summarize the differences, we list few properties of amorphous solids and crystalline solids
- There is only a short range order in amorphous solids.
- Amorphous solids do not have a sharp melting point, they are softened in a range of temperature.
- Amorphous solid undergo irregular or conchoidal breakage.
- Amorphous solids are isotropic.
- They are less rigid.
Examples: Fibre-glass, Cellophane, Teflon, Naphthalene, Polyurethane, Polyvinyl chloride, etc.
- There is long range order in crystalline solids.
- There is a sharp melting point.
- They can be cleaved along definite planes.
- They are anisotropic in nature.
- Crystalline solids are very rigid.
Examples: Copper, Potassium nitrate, Benzoic acid, etc.
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