# Different States of Matter on the Basis of Particle Model

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• 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.

#### 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 at 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 the definite spatial arrangement. Hence solids have a definite shape and definite volume at given temperature and pressure.  When average distance between the particles increases beyond 10-9 m, the solid melts into liquid.

#### 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.

#### 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.

### 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.
• It is to be noted that the chemical properties of a substance do not change with the change in the state of the substance
• The change in physical state and the bulk properties of matter depend on the energy of constituent molecules and intermolecular attraction between them.

### 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.

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