Скачать или смотреть Solid State- Crystalline and Amorphous Solids, Unit Cell and Types, Close Packing, Voids

Solid State-
1. Solids have definite mass, volume and shape and are incompressible and rigid.
2. Intermolecular distances are short and Intermolecular forces are strong.
3. Their constituent particles (atoms, molecules or ions) have fixed
positions and can only oscillate about their mean positions.

Two Types of Solids are there
1. Crystalline Solids or True Solids-
a. It has definite characteristic geometrical shape.
b. It has a long range order
(regular pattern of arrangement of particles which repeats itself
periodically).
c. Melts at a sharp and characteristic
temperature.
d. Give a clean cleavage when cut with sharp edged knife.
e. Anisotropic- Physical properties like electrical conductivity, mechanical strength, refractive index are different in different directions.
Examples- Quartz, NaCl, metals, H2O, HCl, Diamond, Graphite.

2. Amorphous Solids or Pseudo solids-
a. It has an irregular shape.
b. It has a short range order
(regular pattern of arrangement of particles is observed over short distances only).
c. Melts at a range of
temperature.
d. Give an irregular when cut with sharp edged knife.
e. Isotropic- Physical properties like electrical conductivity, mechanical strength, refractive index are same in all directions.
Examples- Quartz glass, Rubber, Plastics, Glass( supercooled liquid) , Amorphous Silicon

Crytalline solids is of 4 types-
1. Ionic solids-
a. Constituent particles are ions held together by electrostatic forces of attraction like NaCl, KI, NaBr
b. They are hard but brittle. Conductors in molten state or aqueous solution.
c. High Melting point

2. Molecular solids-
a. Constituent particles are
i. Non polar molecules held together by london dispersion forces Ar, H2, Cl2, I2
ii. Polar molecules held together by dipole- dipole interactions HCl, HBr, HI, SO2
iii. Hydrogen bonded to F, O or N by Hydrogen Bonding H2O, NH3, HF
b. They are soft and insulators.
c. Low melting point

3. Metallic solids-
a. Constituent particles are positive ions in sea of mobile electrons. Positive ions are held together by metallic bonding like in all metals and alloys.
b. They are hard and good conductors of heat and electricity.
c. High melting point.

4. Covalent/ Network Solids-
a. Constituent particles are atoms(non metals) bonded by covalent bonding like C (diamond, graphite), quartz, AlN
b. They are hard and insulators.
Exception- graphite is soft and good conductor.
c. Very high melting point.

Space lattice/ Crystal Lattice- Three-dimensional
arrangement of atoms/unit cells.

Unit cell- smallest repeating unit of crystal lattice.
Types- 1. Primitive or simple cubic- atoms are present only at corners
2. Centered- atoms are present at another place in addition to corners.
a. Body centered- atoms are present at corners and at body center.
b. Face centered- atoms are present at corners and at center of 6 faces.
c. End centered- atoms are present at corners and at center of 2 opposite faces.

Types of unit cells on the basis of axial angles and axial lengths-
1. Cubic- primitive, body centered, face centered
2. Tetragonal- primitive, body centered
3. Orthorhombic- primitive, body centered, face centered, end centered
4. Trigonal- primitive
5. Hexagonal- primitive
6. Monoclinic- primitive, end centered
7. Triclinic- primitive

Set of 14 unit cells- Bravais lattice

Coordination number- the number of nearest neighbours of any constituent particle.
For 1D packing, CN is 2
For 2D, Square close packing CN is 4
Hexagonal close packing CN is 6
For 3D, hcp( hexagonal close packing) and ccp (cubic close packing) CN is 12

Void- empty space left unoccupied
Tetrahedral void- formed by 4 spheres. When one sphere is placed above 3 spheres. No of tetrahedral voids is equal to double the number of atoms present in a unit cell.
Octahedral void- formed by 6 spheres. When 3 spheres are placed above 3 spheres. No of octahedral voids is equal to the number of atoms present in a unit cell.