Definition of Solids and classification of Solids

Definition of Solids and classification of Solids

Solids and classification of Solids

Solids and classification of Solids is a important topic in chemistry. The solids are the substances which have definite volume as well as definite shape, because the molecules of the substances are closely packed. In terms of kinetic molecular model, solids have regular order of atoms, molecules or ions. These particles are held close together by fairly strong forces, therefore, they maintain a fixed positions in the substance. The properties of a solid depends upon the nature of the as well as on their arrangements in that solid.

Properties:

  • They have a definite mass
  • Definite volume and shape
  • Short intermolecular distance
  • Strong intermolecular forces
  • Rigid and incompressible

Classification of Solids

Crystalline Solid:

                              Crystalline solids or crystals have ordered structures and symmetry. The atoms, molecules or ions in a crystals are arranged in a particular manner, thus, the arrangement should have a long range order in the solid.

In crystalline solids, there is a regular, repeating pattern of the constituents atoms, molecules or ions

What is crystal?

By definition, a crystal is “a homogenous chemical compound with a regular and periodic arrangement of constituents atoms, molecules or ions.”

Examples: halite, salt (NaCl), and quartz (SiO2).

Many people thinks the crystals are founds only in the minerals. But you will be surprised that the crystals are not restricted to minerals. Most of the solid matters such as sugar, diamonds, metals, bones and even DNA.

Solids and classification of Solids

Category of Crystals

Crystals can be categorized according to their physical and chemical properties.

They are-

  • Covalent crystals (e.g.: silicon carbide, diamond),
  • Metallic crystals (e.g.: pyrite),
  • Ionic crystals (e.g.: Calcium chloride)  and
  • Molecular crystals (e.g.: sugar).

Crystals can have different shapes and colors. Crystals have an aesthetic value, and it is believed to have healing properties; thus, people use them to make jewelry.

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Amorphous Solid:

Now we discuss about another type of solid substances. It known as Amorphous solid. Amorphous solid is a solid which does not have a crystalline structure: that means it does not have a long range regular and periodic arrangement of constituents atoms, molecules or ions. It means, it does not have a long range ordered arrangement of constituents atoms, molecules or ions within the structure. So we can say that it is a powder like solid substance.

Glass, gels, thin films, plastics and nano structures materials are some examples for amorphous solids.

Solids and classification of Solids

Definition of Solids and classification of Solids

Differences between crystalline and amorphous solids:

Amorphous Solids

Crystalline Solids

They do not have regular arrangement of particles, therefore do not have well defined particles Crystalline solids have a regular three dimensional arrangement of atoms, ions or molecules due to which they have well defined geometrical shape
They have short range order Crystalline solids have long range order
They do not have sharp melting point i.e., they melt over a range of temperature. They have sharp melting point i.e., they melt at a particular temperature
They do not have fixed heat of fusion. Crystalline solids have high and fixed heat of fusion, i.e., high energy is required to melt 1 mole of crystalline solid
They are isotropic, i.e., they have same properties in all directions. They are anisotropic , i.e., they have different properties such as optical and electrical properties in different directions.
Amorphous solids are unsymmetrical When crystalline solids are rotated about an axis, their appearance does not change. This shows that thay are symmetrical
Amorphous solids don’t break at fixed cleavage planes. Crystalline solids cleavage along particular direction at fixed cleavage planes
They are pseudo – solids, i.e., they do not show all the characteristic properties of solids. They are true solids, i.e., they show all the characteristic properties of solids

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