1. Diffusion and Brownian Motion:
* Diffusion: The gradual spreading of a substance through a medium (like a drop of food coloring in water). This is explained by the random movement of particles, which collide and spread out.
* Brownian Motion: The erratic, jiggling motion of small particles suspended in a fluid (like pollen grains in water). This motion is caused by collisions with the invisible particles of the fluid, demonstrating their existence.
2. States of Matter:
* Solids: Particles are tightly packed and vibrate in fixed positions. This explains their rigid structure and inability to flow.
* Liquids: Particles are closer together than in gases but can move around each other. This explains their ability to flow and take the shape of their container.
* Gases: Particles are far apart and move freely and randomly. This explains their compressibility and ability to fill any container.
3. Chemical Reactions:
* Law of Conservation of Mass: In a chemical reaction, the total mass of reactants equals the total mass of products. This is explained by the rearrangement of atoms (particles) during the reaction, not their destruction or creation.
* Stoichiometry: The fixed ratios of reactants and products in chemical reactions (e.g., 2 hydrogen atoms + 1 oxygen atom = 1 water molecule) are explained by the combining of specific numbers of particles.
4. Physical Properties:
* Boiling Point: The temperature at which a substance changes from liquid to gas. This is explained by the particles gaining enough energy to overcome intermolecular forces holding them together.
* Melting Point: The temperature at which a substance changes from solid to liquid. This is explained by the particles gaining enough energy to overcome the fixed positions they held in the solid state.
5. Atomic Theory:
* Dalton's Atomic Theory: Proposed that elements are made up of tiny, indivisible particles called atoms. This laid the foundation for the idea of particles as the fundamental building blocks of matter.
* Modern Atomic Theory: Explains the structure of atoms with protons, neutrons, and electrons, further solidifying the particle nature of matter.
These pieces of evidence strongly suggest that substances are composed of particles. While we can't directly observe individual particles with the naked eye, the collective behavior of these particles explains a wide range of phenomena we experience in the macroscopic world.
