5.0 PARTICULATE NATURE OF MATTER

Matter is anything that has mass and occupies space. For centuries, scientists debated whether matter was continuous (like a smooth block) or made of tiny particles. We now know that all matter is made of tiny, discrete particles (atoms, molecules, or ions) in constant motion. This chapter explores the evidence for this idea and explains the behaviour of solids, liquids, and gases using the Kinetic Theory of Matter.

5.1 Evidence for the Particulate Nature of Matter

Everyday experiences and simple experiments show that matter is not continuous but consists of tiny particles with spaces between them.

• Dissolving: When sugar or salt dissolves in water, the solid seems to disappear, but the water tastes sweet. The sugar particles separate and fit into the spaces between water particles.
• Expansion and contraction: Solids, liquids, and gases expand when heated. This happens because the particles gain energy and move further apart – if matter were continuous, expansion would be impossible.
• Compressibility of gases: Gases can be squeezed into a smaller volume because there is lots of empty space between particles. Liquids and solids are much harder to compress because their particles are already closely packed.
• Diffusion (see 5.3): The fact that smells spread and ink mixes with water without stirring shows that particles move and intermingle.
• Brownian motion (see 5.2): The