Solids – Definition, Types and Classification

Matter exists in three states in nature – Solid, Liquid and Gas. Solid has a definite shape, whereas liquid and gas flow and take the form of a container. The fluidity of liquids and gas corresponds to weak molecular forces compared to a solid state.

In solids, the constituent particles have a fixed position because of the strong bonding intermolecular forces. Thus, the particles oscillate in their mean positions and are responsible for rigidity in the solid state of matter.

Mainly, Solids are of two types – Crystalline solids and Amorphous solids.

Definition Of Solid

Solid is a form of matter in which the ions, atoms and molecules are held together firmly so that they do not segregate easily from each other. Thus, solids have a definite shape and are rigid.

Properties Of Solid

Solids have five main properties regardless of their type. They are: 

• Solids have definite shapes and volumes.

• They have high density.

• Intermolecular forces between constituent particles are strong. 

• Diffusion of solid into any other form takes a significant amount of time.

• They have a high melting point.

Classification Of Solid State Of Matter

Solids are of two types based on the arrangement of constituent particles: 

• Crystalline solid

• Amorphous solid

Crystalline solids

Solids containing constituent particles of matter organised and arranged in a specific manner are crystalline solids.

Their structure comprises crystals with solid geometry. Also, crystalline solids possess low potential energy and are the most stable form. 

Most of the solids, such as metallic elements (silver, iron and copper), non-metallic elements (Sulphur, Phosphorus and Iodine) and compounds like Zinc Sulphide, Sodium Chloride and Naphthalene, are crystalline solids.

Crystalline Solids are further classified into the following types based on the binding forces between the constituent particles.

• Molecular Solid

• Metallic Solid

• Covalent Solid

• Ionic Solid

Furthermore, molecular solids are classified into three subgroups:

• Non-Polar

• Polar

• Hydrogen-bonded 

Characteristics of Crystalline Solids

The characteristics of crystalline solids are:

• They have a stable structure and predefined geometrical shapes.

• Their freezing point is sharp because the distance between the same atoms/molecules or ions remains constant.

• Because of the fixed regularity in the crystal lattice, the heat of fusion is definite and fixed.

• Crystalline solids are True Solids, and they do not flow like pseudo solids.

• We get a flat and smooth surface by cutting a crystalline solid with a knife.

• They have anisotropic nature, i.e. The properties are different in different directions.

• They depict both the long-range and the short-range order.

Examples are Quartz, Sugar, Calcite, Mica, Diamond etc.

Uses of Crystalline Solids

Some of the prominent crystalline solids and their applications are:

• Diamond is prominently used in making jewellery items.

• Watches and clocks have quartz as their essential component.

• In addition, many industries use various crystalline solids as raw materials in manufacturing consumer goods.

Amorphous Solids

Solids with randomly arranged constituent particles of matter are amorphous solids. They are non-crystalline solids with no specific atom arrangement. Thus, amorphous solids are materials with no typical organised structure of atoms and molecules.

Most solids are amorphous and are used in various sectors. The most common example of an amorphous solid is glass. Glass has many applications in the manufacturing industry.

Characteristics of Amorphous Solids

The main features of amorphous solids are

• The amorphous form of solids has constituent particles of matter arranged randomly. Thus, there is no fixed position of atoms and molecules.

• Due to the random arrangement of atoms and molecules, the amorphous solids lack definite shape or geometry.

• Amorphous solids possess only short-range order.

• They do not form a crystalline structure and can flow. Thus, amorphous solids are also known as pseudo solids or supercooled liquids.

• They are isotropic, i.e., they possess the same properties when measured in all directions. For instance, amorphous solids have the same refractive index.

• They do not have sharp melting points because of irregularly packed atoms and molecules.

• The absence of a sharp melting point also results in no fixed heat of fusion.

• On cutting the amorphous solids, the constituent particles are irregular in shape and geometry.

Examples are Plastics, Rubber, Glass, Polymers, Metallic Glass, Gel etc.

Uses of Amorphous Solids

Some of the widely used amorphous solids and their application are as follows.

• Glass – Used in making tableware, packaging, utensils etc.

• Rubber – Manufacturing of tyres, ropes, footwear etc.

• Polymer – Used in manufacturing medicines, pipes and as a raw material in factories.

• Amorphous Silicon – It is known as the best photovoltaic material used to convert sunlight into electricity.

Classification of Solids on the Basis of Conductivity

Classification of solids based on the conductivity is as follows:

• Conductors

• Semiconductors

• Insulators

Metals or conductors have the highest conductivity, and the insulators have the lowest. Semiconductors have moderate conductivity.

Classification of Solids Based On Magnetic Properties

The classification of solids based on their magnetic properties is as follows:

• Diamagnetic

• Paramagnetic

• Ferromagnetic

• Antiferromagnetic

• Ferrimagnetic

Conclusion

The solid matter of a substance possesses a definite shape and structure and various properties. They are classified into crystalline solids and amorphous solids based on their essential characteristics. Solids are also classified based on their conducting and magnetic properties. This article covers all the crucial facets of solids and their classification. We hope you find this information about solids helpful. Make sure you go through the differences and characteristics of solids, as these are usually asked in exams.