What Is Matter in Our Surroundings Class 9 Notes: Complete Guide

Definition and Basic Properties of Matter

Matter is anything that has mass and occupies space. Everything around us, whether living or non-living, is made up of matter. The three key properties of matter are:

• Mass: The amount of matter present in an object.
• Volume: The space occupied by the matter.
• Inertia: The resistance of matter to change its state of motion.

These properties help us identify and study matter in our surroundings. For example, a book, air, water, and even you are made of matter.

States of Matter and Their Characteristics

Matter exists mainly in three states:

Each state has unique properties. Solids have fixed shape and volume, liquids have fixed volume but no fixed shape, and gases have neither fixed shape nor volume.

Particle Theory of Matter

The particle theory explains the behaviour of matter:

• All matter is made of tiny particles.
• Particles have spaces between them.
• Particles are always moving.
• Particles attract each other.
• The energy of particles changes with temperature.

This theory helps us understand why matter changes state. For example, heating ice increases particle energy, turning solid ice into liquid water.

Changes in States of Matter: Melting, Boiling, and More

Matter changes state when energy is added or removed:

• Melting: Solid to liquid (e.g., ice to water)
• Freezing: Liquid to solid (e.g., water to ice)
• Evaporation: Liquid to gas at any temperature
• Boiling: Liquid to gas at boiling point
• Condensation: Gas to liquid
• Sublimation: Solid directly to gas (e.g., camphor)

These changes depend on temperature and pressure. For example, water boils at 100 °C at normal atmospheric pressure.

Physical and Chemical Changes in Matter

Matter undergoes two types of changes:

• Physical Changes: Change in state or appearance without forming a new substance (e.g., melting, freezing).
• Chemical Changes: New substances are formed with different properties (e.g., burning paper).

Physical changes are usually reversible, while chemical changes are not. Understanding these helps in studying matter’s behaviour in different conditions.

Examples and Formulas Related to Matter

Here are some useful formulas and examples:

• Density ($\rho$): Density is mass per unit volume.

$$\rho = \frac{m}{V}$$

where $m$ = mass (kg), $V$ = volume (m³).

• Example: If a block has a mass of 500 g and volume of 250 cm³, its density is:

$$\rho = \frac{500}{250} = 2 \text{ g/cm}^3$$

• Worked Example: What happens when ice at 0 °C is heated?

• Ice absorbs heat energy.
• Particles vibrate more and break free from fixed positions.
• Ice melts to form water at 0 °C.

This shows matter changing state due to energy changes.