Almost all substances exist in three states under appropriate conditions of temperature and pressure.
1. Solids : Characteristics of solids are as follows :
(i) Have a definite shape and a definite volume.
(ii) Inter molecular forces between the molecules are very strong due to which their positions are fixed. Molecules can only vibrate to and fro about their mean position.
(iii) Molecules are closely packed and associated with minimum energy.
`text(Note) :`
• The melting point of a solid is an indication of strength of inter molecular forces of attraction.
• Melting point of a solid `prop` strength of intermolecular forces.
Solids can be of the following two types :
(i) Amorphous solids : There is no orderly arrangement of constituent particles over the long range. e.g. glass, rubber and plastic etc. Glass is a supercooled liquid.
(ii) Crystalline solids : There is orderly arrangement of constituent particles over the long range. e.g. graphite, diamond, `NaCl` etc.
Crystalline solids can be further classified as :
(a) Ionic solids : Constituent particles are ions and forces of attraction are strong electrostatic forces of attraction e. g. `NaCl , BaCl_2 , ZnS`.
(b) Metallic solids : Constituent particles are positively charged kernels and free electrons. Forces of attraction are metallic bonds. e.g. `Fe, Cu, AI` etc.
(c) Covalent solids : Constituent particles are atoms and forces of attraction are strong covalent bonds. e.g., diamond, quartz, `SiO_2`.
(d) Molecular solids : Constituent particles are molecules and forces of attraction are hydrogen bonds or van der Waals' forces. e.g. solid `CO_2 , I_2` etc.
2. Liquids : Characteristics of liquids are as follows :
(i) No definite shape but have a definite volume.
(ii) Inter molecular forces operating between the molecules are weak due to which they can slide over one another but cannot escape the boundary in normal conditions.
(iii) Molecules are closely packed and associated with intermediate energy due to motion.
3. Gases : Characteristics of gases are as follows :
(i) Neither definite shape nor volume.
(ii) Inter molecular forces operating between the molecules are very weak due to which their positions are not fixed and thus, they can move freely.
(iii) Molecules are wide apart and are associated with maximum energy.
(iv) Gases exert pressure on the walls of the container due to collision of molecules with the walls of the container.
`text(Note)` : Compressibility depends upon the intermolecular spaces between the particles of matter. Order of compressibility or intermolecular spaces is as follows :
Solid < liquid < gas
Almost all substances exist in three states under appropriate conditions of temperature and pressure.
1. Solids : Characteristics of solids are as follows :
(i) Have a definite shape and a definite volume.
(ii) Inter molecular forces between the molecules are very strong due to which their positions are fixed. Molecules can only vibrate to and fro about their mean position.
(iii) Molecules are closely packed and associated with minimum energy.
`text(Note) :`
• The melting point of a solid is an indication of strength of inter molecular forces of attraction.
• Melting point of a solid `prop` strength of intermolecular forces.
Solids can be of the following two types :
(i) Amorphous solids : There is no orderly arrangement of constituent particles over the long range. e.g. glass, rubber and plastic etc. Glass is a supercooled liquid.
(ii) Crystalline solids : There is orderly arrangement of constituent particles over the long range. e.g. graphite, diamond, `NaCl` etc.
Crystalline solids can be further classified as :
(a) Ionic solids : Constituent particles are ions and forces of attraction are strong electrostatic forces of attraction e. g. `NaCl , BaCl_2 , ZnS`.
(b) Metallic solids : Constituent particles are positively charged kernels and free electrons. Forces of attraction are metallic bonds. e.g. `Fe, Cu, AI` etc.
(c) Covalent solids : Constituent particles are atoms and forces of attraction are strong covalent bonds. e.g., diamond, quartz, `SiO_2`.
(d) Molecular solids : Constituent particles are molecules and forces of attraction are hydrogen bonds or van der Waals' forces. e.g. solid `CO_2 , I_2` etc.
2. Liquids : Characteristics of liquids are as follows :
(i) No definite shape but have a definite volume.
(ii) Inter molecular forces operating between the molecules are weak due to which they can slide over one another but cannot escape the boundary in normal conditions.
(iii) Molecules are closely packed and associated with intermediate energy due to motion.
3. Gases : Characteristics of gases are as follows :
(i) Neither definite shape nor volume.
(ii) Inter molecular forces operating between the molecules are very weak due to which their positions are not fixed and thus, they can move freely.
(iii) Molecules are wide apart and are associated with maximum energy.
(iv) Gases exert pressure on the walls of the container due to collision of molecules with the walls of the container.
`text(Note)` : Compressibility depends upon the intermolecular spaces between the particles of matter. Order of compressibility or intermolecular spaces is as follows :
Solid < liquid < gas