Introduction/General characteristics of Solids:
There are three states of matter solid ,liquid and gas. Fluids involve both liquids and gases because of their ability to flow.Solid is a state of matter in which the constituting particles are arranged very closely .The constituent particles can be atoms, molecules or ions.
Properties of solids:
They have definite mass, volume and shape.
They are non compressible and rigid.
Intermolecular distances are very short and hence the intermolecular forces are strong.
Their constituent particles have fixed position. sand can only oscillate about their mean positions.
Classification of solids on the basis of the arrangement of constituent particles:
Properties of crystalline solid
-A solid is said to be crystalline if its various constituent particles [ions, -atoms, molecules] are arranged in a definite geometric pattern in the three dimensional space so that there is short as well as long range order of constituent particles.
-They have a long range order.(means that there is a regular pattern of arrangement of particles which repeats itself periodically over the entire crystal.
-They have a sharp melting point.
-They are anisotropic in nature i.e. their physical properties(such as refractive index, conductivity, thermal expansion) show different values when measured along different directions in the same crystal.
-They have a definite characteristic heat of fusion.
-They are called true solids.
-When cut with a sharp edged tool , they split into two pieces and the newly generated surfaces are plain and smooth.
Example:- Sodium, Calcium, , NaCl and quartz etc.
polymorphs: The different crystalline forms of a substance are known as polymorphic forms or polymorphs . For example: graphite and diamond. Characteristics of amorphous solids:
- If there is no regular arrangement of constituent particles or there is only the short range order of its constituent particles then the solid is called amorphous solid.
-They have a short range order.(In such an arrangement, a regular and periodically repeating pattern is observed over short distances only. Such portions are scattered and in between the arrangement is disordered.
-They gradually soften over a range of temperature.
-They are isotropic in nature i.e. their physical properties are the same in all directions.
-When cut with a sharp edged tool, they cut into two pieces with irregular surfaces.
-They do not have definite heat of fusion.
-They are called pseudo solids or super cooled liquids . This is because they have a tendency to flow, though very slowly.
Example:- Rubber, Glass, Pitch, Silica , quartz glass etc.
Note-supper cooled liquids: A liquid below its freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form.
Amorphous solids are very useful in everyday life such as:
-The glasses [Amorphous] are used in construction house ware, laboratory ware etc.
- A large no. of amorphous plastics is being used in forming no. of articles.
- Amorphous silica has found to be the best material for converting sunlight into electricity [in photovoltaic cells]
CLASSIFICATION OF CRYSTALLINE SOLIDS:-
Based upon nature of constituent particles and binding forces present in them:-
A. Molecular Solids
B. Ionic Solids
C. Metallic Solids
D. Covalent or Network Solids
A. Molecular Solids
In these solids the constituent particles are molecules . they can further subdivided into following three types:-
1. Non polar molecular solids:-
The crystalline solids in which constituent particles are atoms of noble gases [helium, neon] or non polar molecules like [H2, Cl2, I2]
Their characters are:-
-These are soft due to weak intermolecular forces(London force).
- are non conductors of electricity. They have low melting and boiling points.
Examples - Tetra phosphorus decaoxide (P4O10), CO2, CCl4, I2, P4
2. Polar molecular solids
-The crystalline solids in which constituent particles are polar molecules like HCl, SO2 etc. the intermolecular forces of attraction are dipole – dipole forces of attraction.
-their characters are:-
They are soft; they are non conductors of electricity.
Their melting and boiling points are high then non polar solids. They exists gases or liquid at room temperature.
3. Hydrogen bonded – molecular solids:-
In these solids the constituent particles are which contain hydrogen atom linked to high electronegative atoms as N, O, F
Their characters are:-
They exists as volatile liquids or gases at room temperature.
They are non-conductor of electricity.
Their melting and boiling points are high.
Eg: - H2O (ice), NH3.
B. Ionic Solids
Constituent Particles: Ions
Bonding/Attractive Forces: Coulombic or Electrostatic
Electrical Conductivity: Insulators in solid state but conducts in molten state and in aqueous solutions
Physical Nature: Hard but brittle
Melting Point: HighExamples: , ZnS, MgO, NaCl
C. Metallic Solids
In natural the constituent particles are positively charged metal ions – and free electrons.
They are formed of metal atoms which lose their valance electrons to left behind positively charged ions.
These metal atoms are surrounded by the sea of electrons each metal atom contributes one or more electrons to this sea of electrons.
Metallic bond:-
The force that holds the metal kenels (part of metal without valence electrons) and mobile valence electrons in the crystal is called metallic bond.
Properties of metallic solids:-
They possess high electrical and thermal conductivity.
They possess lusture and colour in some case due to presence of sea of free electrons.
They are highly malleable and ductile.
They are closely packed. They exhibit high melting points and high densities.
Examples: Fe ,Cu, Ag, Mg
D. Covalent or Network Solids
In these crystalline solids the constituent particles are non-metal atoms linked to adjacent atom by covalent bond throughout the crystal. They forms a network of covalent bonds and exists as giant molecules. Example: Diamond
Their main characteristics are:-
As covalent bond is strong and directional in nature, these solid are very hard and brittle.
Electrical Conductivity: Conductors in solid state as well as in molten state
Physical Nature: Hard but malleable and ductile
Melting Point: Fairly high
Examples: , (quartz), SiC, C (diamond), C(graphite)
B. Ionic Solids
Constituent Particles: Ions
Bonding/Attractive Forces: Coulombic or Electrostatic
Electrical Conductivity: Insulators in solid state but conducts in molten state and in aqueous solutions
Physical Nature: Hard but brittle
Melting Point: HighExamples: , ZnS, MgO, NaCl
C. Metallic Solids
In natural the constituent particles are positively charged metal ions – and free electrons.
They are formed of metal atoms which lose their valance electrons to left behind positively charged ions.
These metal atoms are surrounded by the sea of electrons each metal atom contributes one or more electrons to this sea of electrons.
Metallic bond:-
The force that holds the metal kenels (part of metal without valence electrons) and mobile valence electrons in the crystal is called metallic bond.
Properties of metallic solids:-
They possess high electrical and thermal conductivity.
They possess lusture and colour in some case due to presence of sea of free electrons.
They are highly malleable and ductile.
They are closely packed. They exhibit high melting points and high densities.
Examples: Fe ,Cu, Ag, Mg
D. Covalent or Network Solids
In these crystalline solids the constituent particles are non-metal atoms linked to adjacent atom by covalent bond throughout the crystal. They forms a network of covalent bonds and exists as giant molecules. Example: Diamond
Their main characteristics are:-
As covalent bond is strong and directional in nature, these solid are very hard and brittle.
Electrical Conductivity: Conductors in solid state as well as in molten state
Physical Nature: Hard but malleable and ductile
Melting Point: Fairly high
Examples: , (quartz), SiC, C (diamond), C(graphite)
B. Ionic Solids
Constituent Particles: Ions
Bonding/Attractive Forces: Coulombic or Electrostatic
Electrical Conductivity: Insulators in solid state but conducts in molten state and in aqueous solutions
Physical Nature: Hard but brittle
Melting Point: HighExamples: , ZnS, MgO, NaCl
C. Metallic Solids
In natural the constituent particles are positively charged metal ions – and free electrons.
They are formed of metal atoms which lose their valance electrons to left behind positively charged ions.
These metal atoms are surrounded by the sea of electrons each metal atom contributes one or more electrons to this sea of electrons.
Metallic bond:-
The force that holds the metal kenels (part of metal without valence electrons) and mobile valence electrons in the crystal is called metallic bond.
Properties of metallic solids:-
They possess high electrical and thermal conductivity.
They possess lusture and colour in some case due to presence of sea of free electrons.
They are highly malleable and ductile.
They are closely packed. They exhibit high melting points and high densities.
Examples: Fe ,Cu, Ag, Mg
D. Covalent or Network Solids
In these crystalline solids the constituent particles are non-metal atoms linked to adjacent atom by covalent bond throughout the crystal. They forms a network of covalent bonds and exists as giant molecules. Example: Diamond
Their main characteristics are:-
As covalent bond is strong and directional in nature, these solid are very hard and brittle.
Electrical Conductivity: Conductors in solid state as well as in molten state
Physical Nature: Hard but malleable and ductile
Melting Point: Fairly high
Examples: , (quartz), SiC, C (diamond), C(graphite)