NCERT Class 8 Science Chapter 7

The particulate nature of matter means that all matter (solids, liquids, and gases) is composed of tiny particles (atoms or molecules) that cannot be seen with the naked eye. These particles have spaces between them, are in constant motion, and attract each other. This concept is central to NCERT Class 8 Science Chapter 7.

Diffusion is the spontaneous spreading of particles from a region of high concentration to a region of low concentration until they are evenly distributed. For example, the smell of perfume spreading across a room is diffusion of gas molecules. Diffusion is faster in gases than in liquids and faster at higher temperatures.

Brownian motion is the random, erratic movement of tiny particles suspended in a fluid (like pollen grains in water) caused by constant collisions with the fluid's moving molecules. It was first observed by botanist Robert Brown in 1827 and provides evidence for the existence and movement of molecules.

Gas particles have very large spaces between them, so they can be pushed closer together easily — gases are highly compressible. Solid particles are very closely packed with almost no space between them, so they cannot be compressed significantly. Liquids fall in between.

As temperature increases, particles gain more kinetic energy and move faster. This is why gases expand when heated, liquids evaporate more quickly at higher temperatures, and diffusion happens faster in warm conditions. The kinetic theory links temperature directly to the speed of particle movement.

Key evidence includes: (1) Diffusion — particles mix on their own, (2) Brownian motion — suspended particles move randomly due to molecular collisions, (3) Dissolution — solutes disappear into solvents as their particles disperse, (4) Compression of gases — spaces between gas particles can be reduced. NCERT Class 8 Chapter 7 explains all these.