Unit – I A
States of Matter
- There are three states of matter, solid, liquid and gaseous.
- liquids and gases are called fluids because of their ability to flow. The fluidity in both of these states is due to the fact that the molecules are free to move about.
- The constituent particles in solids have fixed positions and can only oscillate about their mean positions. This explains the rigidity in solids.
- In crystalline solids, the constituent particles are arranged in regular patterns.
Characteristics of Solid State:
- Solids have definite shape and volume. Generally there density is also definite
- Solids are heavier than liquids and solids. (exception ice is lighter than water). Mercury is in liquid state whose density is very high 13.6 g/cm³
- There are strong cohesive forces between the molecules of solid. The forces between the constituent molecules are stronger than those in liquids and gases.
- The molecules of solid are fixed at one point. Thus they are held tightly at a position by intermolecular forces of attraction. Hence solids can’t be poured.
- Melting point of solid is above the room temperature at the atmospheric pressure. All pure solids have characteristic melting point which depends on intermolecular forces of attraction.
- Most of the solids are hard, incompressible and rigid because due to intermolecular forces of attraction the intermolecular distance is very small.
- the vapour pressure of solid is much less than the vapour pressure of liquids at definite temperature. The particles near surface may possess sufficient kinetic energy to detach from bulk and enter in vapour state.
- The diffusion of solid is negligible.
From above characteristics solid can be defined as a form of matter in which ions, atoms or molecules are held so strongly that they can not easily move past each other. Thus solid is a form of matter which has rigidity and possesses the definite shape and definite volume.
Characteristics of Liquid State:
- Liquids have no definite shape but have definite volume. There density is also definite
- Liquids are lighter than solids but heavier than gases. (exception water is heavier than ice). Mercury is in liquid state whose density is very high 13.6 g/cm³
- There are weaker cohesive forces between the molecules of liquid compared to the cohesive forces between the molecules of solids. There are stronger cohesive forces between the molecules of liquid compared to the cohesive forces between the molecules of gases.
- The molecules of liquid are not fixed at one point. They can move within the bulk of the liquid. Hence liquids can be poured and can be contained in any shape container.
- All pure liquids have characteristic boiling point and freezing point which depends on intermolecular forces of attraction.
Characteristics of Gaseous State:
- Gases have neither definite shape nor definite volume. There density is very small
- Gases are lighter than solids and liquids
- Cohesive forces between the molecules of gases are negligible.
- The molecules of gases are not fixed at one point. The cohesive forces between the molecules of gas are so negligible that the molecules can leave the bulk.