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CBSE | Class 9 | science
Read the chapter in a clean notebook-style flow before moving into deeper practice.
Summary Note
Key concept recap
Matter is anything that occupies space and has mass. It is the fundamental substance that constitutes all the objects in the universe.
Ancient Indian and Greek philosophers believed that matter was composed of basic elements like air, earth, fire, water, and sky.
Modern science classifies matter based on its physical and chemical properties, and in this chapter, the focus is on physical characteristics.
Summary Note
Key concept recap
Matter is made up of particles that are extremely small and not visible to the naked eye.
These particles are arranged in such a way that they have spaces between them, and they are constantly in motion.
The activity of dissolving salt in water and the diffusion of potassium permanganate demonstrate that particles are minute and spread throughout a solution.
Summary Note
Key concept recap
Particles of matter have space between them, allowing one substance to mix into another, as seen in the dissolution of sugar in water.
They are continuously moving, as shown by the spreading smell of incense or perfume.
Particles attract each other, and this force of attraction varies among solids, liquids, and gases.
Summary Note
Key concept recap
Matter exists in three main states: solid, liquid, and gas.
Solids have fixed shapes and volumes, liquids have fixed volumes but take the shape of the container, and gases have neither fixed shape nor volume.
Each state differs in terms of particle arrangement, space, movement, and force of attraction.
Summary Note
Key concept recap
Matter can change from one state to another by altering temperature or pressure.
Melting, boiling, condensation, and freezing are common processes. Melting point and boiling point are fixed for pure substances.
Latent heat is the energy absorbed or released during a change of state without changing temperature.
Summary Note
Key concept recap
Some substances like camphor and naphthalene change directly from solid to gas (sublimation) and vice versa (deposition).
Dry ice (solid carbon dioxide) also undergoes sublimation at room temperature and pressure.
These processes occur without passing through the liquid state.
Summary Note
Key concept recap
Increasing pressure can bring particles closer, converting gases into liquids.
Liquefied gases like LPG and CNG are stored under high pressure for practical usage.
Pressure and temperature together determine the state of a substance.
Summary Note
Key concept recap
Evaporation is the surface phenomenon where liquid changes to vapour at temperatures below boiling point.
Factors affecting evaporation include surface area, temperature, humidity, and wind speed.
Evaporation causes cooling as particles absorb energy from the surroundings to escape into the vapour phase.
Summary Note
Key concept recap
Sprinkling water on roofs and using desert coolers are examples of cooling due to evaporation.
Sweating and wearing cotton clothes in summer help cool the body through evaporation.
Nail polish remover feels cold because it absorbs heat from the palm during evaporation.
Summary Note
Key concept recap
Matter – Anything that has mass and occupies space.
Diffusion – Intermixing of particles of two different substances.
Latent Heat – Heat energy required for changing the state without change in temperature.
Sublimation – Change of state directly from solid to gas.
Deposition – Change of state directly from gas to solid.
Boiling Point – Temperature at which a liquid changes into vapour.
Melting Point – Temperature at which a solid turns into liquid.
Evaporation – Conversion of liquid to vapour from its surface at any temperature below boiling point.
Kinetic Energy – Energy possessed by particles due to their motion.
States of Matter – Solid, liquid, and gas forms of matter based on physical properties.
