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 — from the air we breathe to the chair we sit on — is made of matter. The two fundamental properties of matter are:

• Mass: The amount of matter present in an object.
• Volume: The space occupied by the matter.

Matter exists in three common states: solids, liquids, and gases. These states differ based on the arrangement and movement of their particles. Understanding these basics is crucial for Class 9 students studying NCERT Science.

States of Matter and Their Characteristics

Matter can exist in three primary states:

Each state has unique properties:

• Solids have a definite shape and volume.
• Liquids take the shape of their container but have a fixed volume.
• Gases expand to fill their container, having neither fixed shape nor volume.

This classification helps explain everyday phenomena and is a key part of NCERT Class 9 Science.

Particle Theory of Matter: Understanding Motion and Arrangement

The particle theory explains matter’s properties based on tiny particles:

• All matter is made of extremely small particles.
• Particles have spaces between them.
• Particles are constantly moving; the speed depends on the state.
• Particles attract each other with forces that vary by state.

For example, in solids, particles vibrate but stay fixed; in gases, they move freely at high speeds. This theory helps us understand why matter changes state when heated or cooled, a concept important for Class 9 exams.

Physical Changes in Matter: Melting, Boiling, and Freezing

Physical changes alter matter’s form but not its chemical identity. Important physical changes include:

• Melting: Solid to liquid (e.g., ice to water) at melting point.
• Boiling: Liquid to gas (e.g., water to steam) at boiling point.
• Freezing: Liquid to solid (e.g., water to ice).

These changes depend on temperature and pressure. The melting and boiling points are unique for each substance and help identify it. For example, water melts at 0 °C and boils at 100 °C under normal pressure.

Worked Example:

If the temperature of ice is raised from -10 °C to 10 °C, it first warms to 0 °C, then melts into water at 0 °C, and finally the water temperature rises to 10 °C.

Evaporation and Sublimation: Special State Changes

Besides melting and boiling, matter can change states through:

• Evaporation: Slow vaporization of liquid at temperatures below boiling point, e.g., water drying on a hot day.
• Sublimation: Direct change from solid to gas without becoming liquid, e.g., camphor or dry ice.

These processes are important in daily life and explain natural phenomena like drying clothes or the disappearance of solid air fresheners.

Evaporation depends on surface area, temperature, and humidity, unlike boiling which happens at a fixed temperature.

Summary Table: States of Matter and Their Properties

This table helps Class 9 students quickly compare states of matter for exams.