Chemistry: Particle Model and Substances

Particle Model

• Brownian motion is the random movement of small particles suspended in a liquid or gas due to collisions with smaller, invisible particles.
• Dissolving is the process where a solute mixes with a solvent to form a solution. This process provides evidence for the particle model.
• Brownian motion shows that even particles too small to see have an effect when they collide with larger particles.

Substances

• A substance is a material with a consistent composition and defined properties. Examples include water, gold, and oxygen.
• A mixture contains two or more substances physically combined, but not chemically bonded. Examples include saltwater, air, steel, and sand and water.

Examples of Substances

• Water (H₂O): Composed of two hydrogen atoms and one oxygen atom, having consistent composition and defined boiling/freezing points.
• Gold (Au): Uniform composition with defined physical properties like density and melting point.
• Oxygen (O₂): A pure substance made of oxygen molecules.
• Table salt (NaCl): A pure substance with a consistent chemical formula consisting of sodium and chlorine.

Examples of Mixtures

• Saltwater: A mixture of water and dissolved salt. The salt is physically combined and can be separated by evaporation.
• Air: A mixture of gases (nitrogen, oxygen, carbon dioxide, argon, and water vapor).
• Steel: A mixture of iron, carbon, and sometimes other metals, creating an alloy.
• Sand and water: A physical combination of sand particles and water that can be separated by filtration.

States of Matter

• Foam: A mixture of gas bubbles dispersed in a liquid or solid (e.g., whipped cream).
• Aerosol: A mixture of fine liquid droplets or solid particles suspended in a gas (e.g., spray deodorants)
• In foams, gas particles are trapped within the liquid or solid structure. In aerosols, particles are freely dispersed in the gas.
• A foam forms when small gas bubbles are trapped in a liquid or a solid.