Solid State - Intro, Types, Crystal Lattice, Unit Cell | Chemistry Grade XI

Solid State

Solid State - Intro, Types, Crystal Lattice, Unit Cell | Chemistry Grade XI

Solid State - Detail Introduction

SOLID STATE
Solid is a state of matter in which the particles (atoms, molecules, or ions) are closely packed and the particles are held with each other by a strong force of attraction. Some of the properties of solids are:

  1. They are rigid and have definite volume and shape.
  2. They are incompressible.
  3. They have a high melting point and boiling point.
  4. They have a higher density than liquid and gas.
ANISTROPY AND ISOTROPY
The substance in which the physical properties like mechanical strength, thermal and electric conductivity, refractive index, thermal expansion etc are different in different directions is called anisotropic substance. And this phenomenon is called anisotropy. Crystalline solids are anistrophic solids.

The substance in which the physical properties like mechanical strength, thermal and electric conductivity, refractive index, thermal expansion etc are same in all directions is called isotropic substance. And this phenomenon is known as isotropy. Amorphous solids are isotropic solids.

TYPES OF SOLIDS

  1. Crystalline solids
  2. Amorphous solids

Crystalline solids

Amorphous solids

The substance in which constituent particles are arranged in regular repeating pattern in three dimensional pattern and have fixed  geometry are crystalline solids.

The substance in which the constituents particles are not arranged in regular repeating pattern or fixed pattern and doesn’t have fixed geometry is called amorphous solids.

They are anisotropic solids.

They are isotropic solids.

They are regarded as true solids.

They are not true solids. They are supercooled liquid.

They have high melting point and boiling point.

They have low melting and boiling point.

Examples: NaCl, CuSO45H2O, MgSO4.7H2O, FeSO4.7H2O, etc.

Examples: glass, rubber,plastic,etc

SOME PROPERTIES SHOWN BY CRYSTALLINE SOLIDS

1. Water of crystallization: water molecule associated with the crystal of substance is called water of crystallization. Water of crystallization is an integral part of the crystal of the substance. The substance or the salt which contains water of crystallization is called hydrated substance or hydrated salt. If water of crystallization is removed from hydrated salt, the resulting salt is called anhydrous salt.
Some of the examples of hydrated salt are CuSO4.5H2O, ZnSO4.7H2O, Na2CO3.1OH2O, etc.
 
2. Efflorescence: From hydrated salt or hydrated substance, when they are exposed to atmospheric air, the spontaneous phenomenon of removing one or more water of crystallization is called efflorescence. The substance is called efflorescent substance.
For eg: Na2CO3.10H2O ---------> Na2CO3.9H2O + H2O

3. Hygroscopy: The phenomenon of absorbing moisture from atmospheric air by the substance when they are exposed to atmospheric air is called hygroscopy and the substance is called a hygroscopic substance.

4. Deliquescence: The spontaneous phenomenon of absorbing moisture by the substance till it changes into solution when it is exposed to the atmospheric air is called deliquescence and the substance is called a deliquescent substance. For eg: CaCl2, MgCl2,etc

CRYSTAL LATTICE AND UNIT CELL
The substance which has a fixed geometrical shape with a sharp edge and plane/flat faces is called crystal. The constituent particles are arranged in a regular repeating pattern in three dimensional. The point occupied by a constituent particle in a three-dimensional structure of a crystal is called lattice point or lattice site. The sequence of lattice point in three dimensions is called crystal lattice or space lattice.

The smallest repeating unit of crystal lattice which has a fixed geometrical shape is called unit cell. Unit cell is a fundamental unit of the crystal. Unit cell possesses all the properties which are shown by a crystal.

TYPES OF UNIT CELL

1. Simple unit cell or primitive unit cell: If lattice points occupy only the corners of the unit cell then such unit cell is known as a simple unit cell.

Simple unit cell2. Body-centered unit cell: If lattice point occupies the center of the unit cell as well as corners of the unit cell, then such type of unit cell is known as the body-centered unit cell.

Body centered unit cell3. Face-centered unit cell: If the lattice point occupies the center of all the faces and even the corners of the cell then such unit cell is known as the face-centered unit cell.                   

Face centered unit cell4. End centered unit cell: If the lattice point occupies the centre of opposite faces as well as corners of the unit cell, then such unit cell is known as the end-centered unit cell.

End centered unit cellUNIT CELL OF SODIUM CHLORIDE

Unit cell of sodium chloride

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