0Solid state
Gases are also called fluids because they have tendency to flow. Due to less intermolecular forces between the particles. In solids particles can oscillate about there mean positions. Intermolecular forces keep them closer nd thermal energy keeps them far away.
Crystalline solids and amorphus solids, in crystalline solids large number of small molecules are present they have long range order molecules but all molecules have definite shape in solids two things matter structure and properties of molecules. NaCl and Quartz are examples of crystalline. Amorphous solids consist of particles of irregular shape they have short range order. Quartz glass is example of amorphous solids. Amorphous solids is similar to liquids.
Glass, Plastics, Rubber also example of amorphous solids. Crystalline solids have sharp melting point. Amorphous solids become soften on short range of temperature on heating they become crystalline at some temperature.
Glasses from ancient times have a tendency to flow, though very slowly. Therefore they are called pseudo solids nd supercooled liquids.
Glasses panes fixed to windows or doors of old buildings are found invariably slightly thicker at the bottom rather than top because glass flows down from top to bottom.
Crystalline solids are anistropic in nature means their electrical resistance, refractive index show different values in different directions. Amorphous solids are isotropic. Because they have short range order arrangement and molecules are not arranged properly therefore they show same properties in any direction.
Amorphous solids are useful materials. Amorphous solids is best photovoltic material for conversion of sunlight into electricity. Mostly solids are crystalline solids like all metallic and non metallic elements along with some compounds like Nacl. Crystalline solids are classified on the basis of forces held between them.
Classification of crystalline solids:
Molecular solids:
1. Non polar molecular solids: These solids are generally found in the state of gaseous or liquid state at room temperature and pressure.these solids generally comprise of atoms like Argon and Heleium and molecules which are held by weak dispersion forces. They are not conductor of electricity.
2. Polar molecular solids: These solids are formed by stronger polar covalent bonds. The molecules in these solids are held by strong dipole-dipole intrection. They are soft solids and are not conductors of electricity. They are soft solids. High melting point rather than previous one most of the gases and liquids are these type of solids under room temperature and pressure. Solid Ammonia and SO2.
3. Hydrogen bonded solids: These solids are formed by strong polar covalent bonds. The molecules of such solids contain polar covalent bonds between H, F, O and N atoms. H2O(solid) is example in which strong hydrogen bond is present.
Ionic solids: These solids formed by three dimensional arrrangement of cations and anions. And these are held by strong electrostatic forces. They are hard and brittle in nature. They cannot conduct electricity in solid state because ions are not free to move about but conduct in liquid state. They have high melting and boiling points.
Metallic solids: In these type of solids positive ions are surronded by sea of negative charged electrons. These free electrons are free to move and evenly spread throughout the crystal. These free electrons are held responsible for electrical and thermal conductivities. When electric field is applied then each electron flow through the network of positive ions. When thermal heat is provided then heat will spread over the surface of metal by free electrons. they have high melting point. malleable and ductile.
Covalent or network solids: Covalent bonds are strong and directional in nature. Therefore atoms are held by strong molecular forces. Very hard and brittle. They are non conductor of electricity. They have very high melting point and may even decompose before melting.
Diamond and Silicon Carbide are the examples.
