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Types and Classification of solids

Types and Classification of solids

(1) Types of solids

Solids can be broadly classified into following two types,

(i) Crystalline solids/True solids,

(ii) Amorphous solids/Pseudo solids

Crystalline solids Amorphous solids
They have long range order. They have short range order.
They have definite melting point Not have definite melting point
They have a definite heat of fusion Not have definite heat of fusion
They are rigid and incompressible Not be compressed to any appreciable extent
They are given cleavage i.e. they break into two pieces with plane surfaces They are given irregular cleavage i.e. they break into two pieces with irregular surface
They are anisotropic because of these substances show different property in different direction They are isotropic because of these substances show same property in all directions
There is a sudden change in volume when it melts. There is no sudden change in volume on melting.
These possess symmetry Not possess any symmetry.
These possess interfacial angles. Not possess interfacial angles.

(2) Crystalline and amorphous silica

Silica occurs in crystalline as well as amorphous states. Quartz is a typical example of crystalline silica. Quartz and the amorphous silica differ considerably in their properties.

Quartz Amorphous silica
It is crystalline in nature It is light (fluffy) white powder
All four corners of tetrahedron are shared by others to give a network solid The tetrahedra are randomly joined, giving rise to polymeric chains, sheets or three-dimensional units
It has high and sharp melting point (1710°C) It does not have sharp melting point

(3) Diamond and graphite

Diamond and graphite are tow allotropes of carbon. Diamond and graphite both are covalent crystals. But, they differ considerably in their properties.

Diamond Graphite
It occurs naturally in free state It occurs naturally, as well as manufactured artificially
It is the hardest natural substance known. It is soft and greasy to touch
It has high relative density (about 3.5) Its relative density is 2.3
It is transparent and has high refractive index (2.45) It has black in colour and opaque
It is non-conductor of heat and electricity. Graphite is a good conductor of heat and electricity
It burns in air at 900°C to give CO2 It burns in air at 700°C to give CO2
It occurs as octahedral crystals It occurs as hexagonal crystals

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