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:
- They are rigid and have definite volume and shape.
- They are incompressible.
- They have a high melting point and boiling point.
- They have a higher density than liquid and gas.
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
- Crystalline solids
- Amorphous solids
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Crystalline solids |
Amorphous solids |
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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. |
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They are anisotropic solids. |
They are isotropic solids. |
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They are regarded as true solids. |
They are not true solids. They are supercooled liquid. |
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They have high melting point and boiling point. |
They have low melting and boiling point. |
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Examples: NaCl, CuSO45H2O, MgSO4.7H2O, FeSO4.7H2O, etc. |
Examples: glass, rubber,plastic,etc |
SOME PROPERTIES SHOWN BY CRYSTALLINE SOLIDS
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
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.
2. 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.
3. 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.
4. 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.
UNIT CELL OF SODIUM CHLORIDE
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