Solid State (Lec-1) | Crystalline & Amorphous Solids | Isotropy & Anisotropy Nature of Solids

In this particular Lecture, we discussed a brief introduction about solids and also classified it on the basis of nature of order in the arrangement of its constituent particles i.e. Crystalline and amorphous solids. Additionally, we also discussed the isotropic and anisotropic behaviour of solids in very concise and symmetrical manner. 

I hope this information will help you in your preparation. If you have any doubt, let me ask freely in the COMMENT box.

What is Solid State

The vast majority of solid substances like high temperature superconductors, biocompatible plastics, silicon chips, etc. are destined to play an ever expanding role in future development of science.

We are mostly surrounded by solids and we use them more often than liquids and gases. For different applications we need solids with widely different properties. These properties depend upon the nature of constituent particles and the binding forces operating between them. Therefore, study of the structure of solids is important. The correlation between structure and properties helps in discovering new solid materials with desired properties like high temperature superconductors, magnetic materials, biodegradable polymers for packaging, biocompliant solids for surgical implants, etc. 

General Characteristics of Solid State

The solids are the substances which have definite volume and definnite shape. in terms of kinetic molecular model, solids have regular order of their constituent particles like atoms, molecules, or ions. These particles are held together by fairly strong forces., therefore, they are present at fixed positions. The properties of the solids not only depend upon the nature of the constituents but also on their arrangements.The following are the characteristic properties of the solid state: 

1. They have definite mass, volume and shape.
2. Intermolecular distances are short.
3. Intermolecular forces are strong.
4. Their constituent particles (atoms, molecules or ions) have fixed positions and can only oscillate about their mean positions.
5. They are incompressible and rigid.

Types and Classification of Solids

On the basis of the nature of order present in the arrangement of their constituent particles,  solids can be broadly classified into following two types,

1. Crystalline solids/True solids

2. Amorphous solids/Pseudo solids

A crystalline solid usually consists of a large number of small crystals, each of them having a definite characteristic geometrical shape. In a crystal, the arrangement of constituent particles (atoms, molecules or ions) is ordered. It has long range order which means that there is a regular pattern of arrangement of particles which repeats itself periodically over the entire crystal. Sodium chloride and quartz are typical examples of crystalline solids.

An amorphous solid (Greek amorphos = no form) consists of particles of irregular shape. The arrangement of constituent particles (atoms, molecules or ions) in such a solid has only short range order. In such an arrangement, a regular and periodically repeating pattern is observed over short distances only. Such portions are scattered and in between the arrangement is disordered. The structures of quartz (crystalline) and quartz glass (amorphous) are shown in Fig. 1.1 (a) and (b) respectively. 

While the two structures are almost identical, yet in the case of amorphous quartz glass there is no long range order. The structure of amorphous solids is similar to that of liquids. Glass, rubber and plastics are typical examples of amorphous solids.

Distinction between Crystalline and Amorphous Solids

1. Crystalline solids have long range order whereas amorphous solids have short range order.
2. Crystalline solid have definite melting point whereas amorphous solid melt over a range of temprature.
3. Crystalline solids have a definite and characteristic heat of fusion whereas amorphous solids do not have definite heat of fussion.
4. Crystalline solids are given smoth cleavage i.e. they break into two pieces with plane surfaces whereas amorphous solids are given irregular cleavage i.e. they break into two pieces with irregular surfaces.
5. Crystalline solids are anisotropic in nature i.e. show different properties in different direction Whereas amorphous solids are isotropic in nature i.e. show same properties in different direction.
6. Crystalline solids possess symmetry whereas amorphous solid do not possess symmetry.
7. Quartz, Metal (Na, Fe, Ca, Cu, etc), Benzoic acid, Naphthaline, Diamond, Graphite, Sugar, Salt etc are the examples of crystalline solid whereas glass, polymers, charcoal, coal, rubber etc are the examples of amorphous solid.

Isotropy & Anisotropy Nature of Solids

If we measure some physical Properties like electrical conductivity, resistance. thermal conductivity, mechanical strength and refractive index etc. of solid along with a perticular direction then crystalline solid show different physical properties in different direction which is known as anisotropy and the substances which shows these properties is called Anisotropic. Whereas amorphous solid show same physical properties in all direction which is known as isotropy and the substances which shows these properties is called isotropic.

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