The Solid State

Solid: A substance which has the melting point above the room temperature under normal pressure is called a solid. Ex: iron, rubber, plastic etc.

Rigidity in solids: The constituent particles in solids have fixed positions. They can’t move like those in fluids(Liquids & Gases). These particles can only oscillate about there mean positions. This property of solid leads to rigidity. Only due to this the solids have definite shape and volume.

Existence of a state: At the given temperature & pressure, the state of a matter depends upon two factors – the intermolecular forces & thermal energy.

The intermolecular forces are for keeping the constituent particles(molecules or ions or atoms) together.

Thermal energy is responsible for keeping them apart due to which they move faster.

When the temperature is low, the thermal energy is also low. In such a situation intermolecular forces become very strong and they bring the constituent particles very close. Thus, the particles are at fixed positions and a definite shape is formed.

Properties of solids: Solids have following properties:

I. They has definite mass, volume & shape.

II. The intermolecular distances are short.

III. Intermolecular forces are very strong.

IV. The constituent particles have fixed positions and can only oscillate about their mean positions.

Types of solids: Solids can be classified as two types: 1.Crystalline solids & 2.Amorphous solids

1.Crystalline Solids: A solid made up of a large number of crystals is called a crystalline solid. A crystal is an ordered arrangement of particles(molecules, atoms or ions).

Ex: Sodium Chloride(NaCl), quartz etc

2.Amorphous solid: A solid is called amorphous when its constituent particles are irregularly arranged.

Ex: Quartz glass, rubber, plastic etc

Difference between crystalline & amorphous solids:

Property Crystalline Solids Amorphous Solids
Shape Definite Geometrical Shape Irregular Shape
Nature True solids Pseudo solids or super cooled liquids
Melting Point Melt at a sharp & characteristic temperature Melt over a certain range of temperature
Heat of fusion Have definite and characteristic heat of fusion Don’t have a definite heat of fusion
Order of arrangement Long range order Only short range order
Cleavage Property Have a clean cleavage when cut Have irregular cleavage when cut
Anisotropy Anisotropic Isotropic

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