Classification of Solids
Solids are classified into two main classes.
- Crystalline
- Amorphous
Crystalline Solids
In a solid if the atoms are attached with each other with a definite arrangement and it also possesses a definite geometrical shape. This type of solid is called crystalline solid.
e.g. NaCl, NiSO4 are crystalline solids.
Amorphous Solids
In these solids there is no definite arrangement of the particles so they do not have a definite shape. The particles of such solids have a random three dimensional arrangement. Examples of amorphous solids are glass, rubber, plastic etc.
The properties of crystalline and amorphous solids are quite different from each other. These differences in properties are given below.
Difference of Geometry
Crystalline Solids
In crystalline solids particles are arranged in a definite order due to which it possesses a definite structure.
Amorphous Solids
In amorphous solids particles are present without any definite arrangement so they do not have definite shape.
Difference of Melting Point
Crystalline Solids
Crystalline solids have sharp melting point due to uniform arrangement.
Amorphous Solids
Amorphous solids melts over a wide range of temperature
Cleavage and Cleavage Plane
Crystalline Solids
When a big crystal is broken down into smaller pieces the shape of the smaller crystals is identical with the bigger crystal. This property of crystalline solids is called cleavage and the plane from where a big crystal is broken is called cleavage plane.
Amorphous Solids
Amorphous solids do not break up into smaller pieces with an identical shape.
Anisotropy & Isotropy
Crystalline Solids
It is a property of crystalline solid that they show different physical properties in different direction. For example graphite can conduct electric current only through the plane which is parallel to its layers. This property is called anisotropy.
Amorphous
In amorphous solids the physical properties are same in all directions. This property of solids is called isotropy.
Symmetry in Structure
- Crystalline solids are symmetric in their structure when they are rotated about an axis, their appearance remains same so they are symmetric in structure.
- Amorphous Solids are not symmetric
