Classification of Solid chapter 1 Solid State Chemistry for class 12th

Classification of solid based upon particle arrangement:

Depending upon the arrangement of constituent particles solid can be classified into two types:

  1. Crystalline solids,
  2. Amorphous solids.

Crystalline solids : Classification of Solid

These are the solids in which the constituent particles ( atoms, ions or molecules) have a regular orderly arrangement throughout and its get repeated again and again resulting in definite pattern.

We can say that these solids have long-range order. A crystalline solid therefore, has a large number of units called crystals. A crystals may therefore be defined as: A solid figure having a definite geometrical shape with flat faces and sharp edges.

Crystalline solids are known as True solids. Some Examples of crystalline solids are sodium chloride, sucrose (sugar), diamond, quartz and all solid metals and non metals.

Amorphous solids :

The term ‘amorphous’ is derived from a Greek word ‘Omorphe’ meaning shapeless indicating thereby that the amorphous solids do not have a regular arrangement of their constituents particles.

However in some cases, they may have small regions of orderly arrangement in which they behave like crystalline solids. Such regions are called crystallates. Thus, the amorphous solids have a short-range order.

The long-range order of crystalline solid and short-range order in the amorphous solids arr being illustrated by the two-dimensional structures of quartz glass in fig. 1.1 although both the structures look to be identical but there is no long-range order in structure (b) for this reasons, whereas crystalline solids have definite geometrical shapes, amorphous solids have irregular shape.

Classification of Solid
Fig. 1.1 Representation of (a) long-range order (b) short-range order (quartz glasss). Classification of Solid

Amorphous solids are quite often called Pseudo solids. A few common examples of amorphous solid are glass, rubber, strarch, cellulose, plastics, ( Infact all Polymers).

Distinction Between Crystalline and Amorphous Solids ,Classification of Solid

The main points of different between the two types of solids are briefly discussed:

  1. Geometry: Crystalline solids have definite and regular geometry which extends through the crystals i.e. these solids have long-range order whereas amorphous solids do not have definite orderly arrangements. At the most these can be orderly arranged to 10-10m i.e., they have short-range order.
  2. Melting points : The crystalline substance possess sharp melting points whereas the amorphous substances melts gradually over a temperature range. That is only glasses and plastics soften over a  temperature range and can be moulded or blown into various shapes. Amorphous solids do not possess definite heats of fusion.
  3. Isotropy and Anisotropy : Crystalline solids are anistropic in nature that means they have different values of physical propeerties ( such as refractive index, density etc. ) at different direction of solids, because crystalline solids have different arrangement of constituent particle in different directions of solids.
    Classification of Solids
    Fig 1.2 Anisotropy in crystallinen solids.

    On the other hand, amorphous solids are isotropic in nature. It is due to the reason that the arrangement of particles is irregular in all directions and hence the values of any physical property would be same along any direction.

  4. Cleavage with a knife: A crystalline solid when cut with a sharped edge tool such as knife gives a clean cleavage but an amorphous solids undergoes irregular cleavage. this has been shown in fig.1.3.
Classification of Solids
Fig 1.3. Cleavage of a crystalline and Amorphous solids .

Thus, the main points of different between a crystalline solid and an amorphous solid may be summed up as follows:

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