NCERT Gist: Matter In Our Surroundings | Additional Study Material for UPSC PDF Download

- Everything in this universe is made up of material which scientists have named “matter” which occupy space and have mass.
- Early Indian philosophers classified matter in the form of five basic elements - the “Panch Tatva”- air, earth, fire, sky and water.
- Modern day scientists have evolved two types of classification of matter based on their physical properties and chemical nature.
- The particles of matter are very small - they are small beyond our imagination.
- Particles of matter have space between them.
- Particles of Matter are continuously moving.
- With increase in temperature the kinetic energy of the particles also increases.
- Particles of matter intermix on their own with each other by getting into the spaces between the particles.
- Intermixing of particles of two different types of matter on their own is called diffusion.
- On heating, diffusion becomes faster.
- Matter around us exists in three different states- solid, liquid and gas.
- These states of matter arise due to the variation in the characteristics of the particles of matter.

The Solid State

- Have a tendency to maintain their shape when subjected to outside force.
- Break under force but it is difficult to change their shape, so they are rigid.

The Liquid State

- Liquids have no fixed shape but have a fixed volume.
- Take up the shape of the container in which they are kept.
- Flow and change shape, so they are not rigid but can be called fluid.
- Solids, liquids and gases can diffuse into liquids.
- The rate of diffusion of liquids is higher than that of solids.
- This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state.

The Gaseous State

- Highly compressible as compared to solids and liquids.
- Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.
- On increasing the temperature of solids, the kinetic energy of the particles increases.
- Due to the increase in kinetic energy, the particles start vibrating with greater speed.
- The energy supplied by heat overcomes the forces of attraction between the particles.
- The particles leave their fixed positions and start moving more freely.
- A stage is reached when the solid melts and is converted to a liquid.
- The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
- The melting point of a solid is an indication of the strength of the force of attraction between its particles.
- The process of melting, that is, change of solid state into liquid state is also known as fusion.
- When a solid melts, its temperature remains the same.
- The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent (HIDDEN) heat of fusion.
- The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon.
- A change of state directly from solid to gas without changing into liquid state (or vice versa) is called sublimation.
- Solid carbon dioxide (CO₂) is stored under high pressure.
- Solid CO₂ gets converted directly to gaseous state on decrease of pressure to 1 atmosphere without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.
- Pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.
- Change of a liquid into vapours at any temperature below its boiling point is called evaporation.
- The rate of evaporation increases with an increase of surface area: evaporation is a surface phenomenon, an increase of temperature,
- A decrease in humidity, an increase in wind speed: Evaporation causes cooling.