General characteristics of solid

• A.  Solid substance has a definite volume and  a. Definite shape
• A solid is rigid and it cannot be compressed easily
• A solid does not diffuse into another solid
• Heat energy is needed to melt a solid

Types of solids

Of the three states of matter solids have always attracted considerable interest because of their symmetry ,beauty and simplicity of form. The solid substances have been classified as crystalline and amorphous solids.

Crystalline solids:- The solids having sharp edges and well define plane are called crystals. Crystalline solids are called true solids. Sodium chloride, quartz, gold, copper and iron are some examples of crystalline solids.

Amorphous solids:- The solids which lack in well defined structure are known as amorphous (a=without, morph= form i.e., without form). Amorphous are also called pseudo solids. Glass, rubber and plastics are some examples of amorphous solids.

Difference between the crystalline and amorphous solids.

These two solids are differ with respect to the internal arrangements of their constituent particles, melting point and anisotropy.

1. Internal arrangement of the constituent particles:- In a crystalline solids the constituent particles are regularly arranged. A crystal has a long range order. On the other hand, an amorphous solids does not have long-range order.
2. Melting point:- A crystalline solid has sharp melting point. But amorphous solids on heating gradually soften and changes into viscous fluid. Thus an amorphous solids do not have sharp melting point.
3. Enthalpy of fusion:- A crystalline solid has a definite characteristic enthalpy of fusion. But the enthalpy of fusion of an amorphous solid is not fixed.
4. Anisotropy:- Dependence of electrical and optical properties of the same solid on the direction of its measurement is called anisotropy.

          A crystalline substance shows anisotropy. For example, a ray of light splits into separate components when it passed through a crystalline solid. The components of light follow different paths in the same crystalline solid.

          An amorphous substance is isotropic and has identical characteristics in all the directions.

       5. Cleavage:- A crystalline solids can be cut with sharp knife produces plane and smooth surface. But on cutting with sharp knife an amorphous solids produces irregular surfaces.

Difference between amorphous and crystalline solids are tabulated below :-

property	crystalline solids	Amorphous solids
Structure	In the crystalline solids their constituent particles were arrangement in a regular pattern having long range order	In Amorphous solids their constituent particles do not have definite geometry for a long rage order
Melting point	crystalline sounds having sharp melting point	They have broad melting point
cleavage	Crystals can be cleaved along definite planes.	Cleavage of an amorphous solid gives irregular plane.
Electrical and optical nature	Crystalline substance are anisotropic in nature: They have different electrical and optical properties along different planes of the same crystal	Amorphous substance are isotropic in nature: They have identical electrical and electrical properties in all direction

Did you know:- A crystalline solid can be changed into amorphous solid by melting and rapid cooling of the object

Use of amorphous solids

# Amorphous silica is used as photovoltaic to convert sunlight into electricity.

# Amorphous solids are useful as inorganic glasses, in fabrication of glass, apparatus for laboratory, and making of glass kitchenwares..

Question time

The refractive index of a solid substance has the same value in all directions. What is the nature of the solid ? Would it have a sharp melting point?

Ans:- The substance is isotropic and thus it is an amorphous solid. Therefore, it would not have sharp melting point.