Chapter 1 Class 9 Science Exam Oriented Notes

🔹 Characteristics of Particles of Matter

1️⃣ Particles of matter have space between them

 Demonstrated by dissolving salt/sugar in water.

 Shows that particles are not tightly packed.

2️⃣ Particles of matter are in continuous motion

 Particles move constantly.

 Motion increases on heating.

 This movement is called diffusion.

3️⃣ Particles of matter attract each other

 Attractive force keeps particles together.

 Strongest in solids, weakest in gases.



🔹 States of Matter

There are three main states of matter:

1. Solid

2. Liquid

3. Gas



🔹 Solids

Properties:

 Fixed shape and fixed volume

 Rigid and incompressible

 Strong inter-particle force

 Very less space between particles

Examples: Ice, iron, wood, stone



🔹 Liquids

Properties:

 Fixed volume but no fixed shape

,  Can flow

 Less rigid than solids

 Moderate inter-particle force

Examples: Water, milk, oil



🔹 Gases

Properties:

 No fixed shape and no fixed volume

 Highly compressible

 Weak inter-particle force

 High diffusion rate

Examples: Oxygen, carbon dioxide, LPG



🔹 Comparison of States of Matter (Important for Exam)

Property Solid Liquid Gas

Not Not
Shape Fixed
fixed fixed

Not
Volume Fixed Fixed
fixed

Compressibili Very Very
Low
ty low high

Very
Diffusion Slow Fast
slow



🔹 Diffusion

Diffusion is the movement of particles from a region of higher
concentration to lower concentration.

 Fastest in gases

 Slowest in solids

Example: Smell of perfume spreading in a room.