Science > Chemistry > States of Matter > Introducion
A matter is defined as anything that has mass, which occupies space and may be perceived by senses. There are three states of matter, viz. (a) solid, (b) liquid, and (c) gaseous states.
Historical Perspective of States of Matter:
Ancient Indian philosophers suggested that all the forms of matter are made up of five basic elements (they called it tatva) they called these five basic elements as ‘panch maha bhoota’. These elements are the sky (Akash), air (vayu), fire (teja), water (aap) and earth (soil). Ancient Greek philosophers considered that all for of matter are made of fire, water, air and the earth. Thales (640-546 BC) suggested that all things arose from the water.
The properties which decide the state of matter are the interparticle space, the force of attraction between particles, and the kinetic energy of particles due to their motion. Thus different states of matter can be explained on the basis of particle and kinetic model.
Solid State:
It has a definite shape and definite volume at a given temperature and pressure. A substance is said to be in the solid state if its melting point is above the room temperature at the atmospheric pressure e.g. Chair, chalk, desk, salt, silver, etc.
Characteristics of Solid State:
- Solids have a definite shape and volume.
- There are strong cohesive forces between the molecules of solid.
- The molecules of solid are fixed at one point.
- The melting point of the solid is above room temperature at atmospheric pressure.
- Solids have high densities.
Particle Model:
According to the particle model, in the solid state, the constituent particles are very close to each other. Hence voids between them are very small. There are strong cohesive forces between the particles of solid.
Due to small voids and strong cohesive forces, the particles are not free to change their position and thus can’t have relative motion w.r.t. each other. Thus the particles of solid are fixed at one point. Hence solids have a definite shape and definite volume at given temperature and pressure.
Kinetic Model:
Due to small interparticle space and strong cohesive forces, the particles are fixed in one position. They can only vibrate about their mean position. Hence solids have low thermal energy and thus particles cannot break away from each other by overcoming inter-particles attractive forces. Thus they have a definite spatial arrangement. Hence solids have a definite shape and definite volume at a given temperature and pressure. When the average distance between the particles increases beyond 10-9 m, the solid melts into a liquid.
Liquid State:
It has a definite volume but has indefinite shape. It will take the shape of the container containing it. A substance is said to be in the liquid state if its boiling point is above the room temperature and melting point is above the room temperature at the atmospheric pressure e.g. water, alcohol, milk etc.
Characteristics of Liquid State:
- Liquids do not have a definite shape but have a definite volume
- In liquids, the cohesive forces are weaker compared to solid and stronger compared to gases.
- Molecules of liquid move freely anywhere but can’t leave the bulk.
- The boiling point of a liquid is above and its freezing point (melting point) is below the room temperature at the atmospheric pressure.
- Liquids have comparatively low densities compared to solids but have higher densities than gases.
Particle Model:
According to the particle model, in the liquid state, the distance between constituent particles is more compared to that between solid particles and less than that between gaseous particles. Thus voids are more compared to that in solids but less compared to that in gases. The cohesive forces between the particles of a liquid are weaker than that between solid particles and stronger than that between gaseous particles.
Hence the cohesive forces are weak enough so that the particles of liquid can have relative motion w.r.t. each other but these cohesive forces are strong enough to stop the particles of a liquid to go out of the bulk. Hence liquids have a definite volume but have indefinite shape.
Kinetic Model:
The interparticle distance between the particles is more than that in the solid state. Hence the attractive forces are weaker than that in the solid state. There is larger void space among the particles. Hence the particles can vibrate with a higher amplitude. At the same time, the particles can move in the bulk. Hence they have translational motion.
Thus particles in the solid state have more thermal energy than that in the solid state. Thus liquids can flow and have a definite volume. Due to their fluidity, they acquire the shape of the container in which they are kept.
Gaseous State:
Gas has neither a definite shape nor a definite volume. It takes the shape and volume of the container. Thus it occupies the whole available volume. A substance is said to be in the gaseous state if its boiling point is below room temperature at atmospheric pressure. e.g. air, oxygen, nitrogen, carbon dioxide.
Characteristics of Gaseous State:
- Gases have neither definite shape nor a definite volume.
- In gases, the intermolecular forces of attraction are very weak i.e. almost zero.
- Molecules of gases move freely anywhere.
- The condensation point (boiling point) of gas is below the room temperature at atmospheric pressure.
- Gases have very low densities.
Particle Model:
According to the particle model, iIn the gaseous state, the distance between constituent particles is very large compared to that between solid particles of the liquid. Voids are very large. The cohesive forces between the particles of a gas are negligible. Hence the particles of a gas can move away freely from the bulk and occupy any space available. Hence, gases have neither a definite shape nor a definite volume.
Kinetic Model:
In the gaseous state, the distance between constituent particles is very large compared to that between solid particles of the liquid. The cohesive forces between the particles of a gas are negligible. Hence the particles are free to move and free to vibrate. Hence they have the highest kinetic energy (hence thermal energy) in this state compared to the solid and liquid state.
On cooling the gas the kinetic energy of the gas particles decreases and the molecules come near to each other resulting in an increase in the cohesive forces and thus the gas condenses to form a liquid.
Notes:
- By changing the temperature or pressure or both, the state of the substance can be changed.
- Besides these three standard states of matter, there are two more states called plasma state (Exists at very high temperature) and Bose-Einstein condensate (Exists at the very very cold condition).
Comparative Study of States of Matter:
| Parameter | Solids | Liquids | Gases |
| Mass | Definite mass | Definite mass | Definite mass |
| Volume | Definite volume | Definite volume | No Definite volume. Occupies the whole volume of the container. |
| Particles | Closely packed | Loosely packed | Very loosely packed |
| Interparticle space | Very low | More than solid less than gases | Highest |
| Interparticle forces | Highest | Weaker than solid | Negligible |
| Packing of particles | Closely packed | Loosely packed | Very loosely packed |
| Constraint of particles | Fixed at one position | Free to move in bulk | Free to move anywhere |
| Motion of particles | vibratory | Vibratory, translational, rotational | Vibratory, translational, rotational in all directions |
| Kinetic energy of particles | Lowest | More than solids less than gases | Highest |
| Thermal energy of particles | Lowest | More than solids less than gases | Highest |
| Free surface | Infinite | One | No free surface |
| Density | High density | More than solids but less than gases | Low density |
| Fluidity | rigid | Fluid | Fluid |
| Compressibility | In compressible | Slightly compressible | Highly compressible |
| Thermal expansion | Very low | Higher than solid | Much higher than solids and gases |
| Melting point | Very high | For their solid state it is below atmospheric temperature | For their solid state very very low |
| Boiling point | For their liquid state very high | low | For their liquid state very very low |
| Diffusion | No diffusion | Some liquids can diffuse spontaneously (alcohol + water), other are immiscible. | Highly diffusible with high rate. |
Plasma State:
This state exists at superheated gaseous state consisting of a mixture of electrons and positively charged ions with unusual properties. These particles are super energetic and are at super excited state. It is found at extremely high temperatures such as interiors of suns and stars or intense electric fields as a discharge tube. Astronomers reveal that 99% of all matter in the universe exists in the plasma state.
Bose-Einstein Condensate (1924):
This state was predicted by Einstein and proved by Satyendra Nath Bose in 1920. It is super cooled solid in which atoms lose their separate identity. They get condensed and behave like a single super atom. This state is very useful for the modern concept of superconductivity.
Bulk Properties of Matter:
The bulk properties of matter depict the collective behaviour of a large number of particles taken together. These properties are not exhibited by the particle individually.
Volume, pressure, temperature, melting point, boiling point, vapour pressure, density, surface tension, viscosity etc. are the bulk properties of matter.
Bulk properties of matter are dependent on the state of the matter and they change with the change in the state of the matter. Similarly, these bulk properties depend on the energy of constituent particles and electrostatic attraction between them. The change in the physical state and the bulk properties of matter depend on the energy of constituent molecules and intermolecular attraction between them.
It is to be noted that the chemical properties of a substance do not change with the change in the state of the substance