Overview
This lecture explains how to classify materials into four categories: heterogeneous mixture, homogeneous solution, homogeneous pure substance (element), and homogeneous pure substance (compound).
Categories of Material
- All materials are made of chemical elements, either alone or combined.
- Material classifications: heterogeneous mixture, homogeneous solution, homogeneous pure substance element, homogeneous pure substance compound.
Mixtures
- Heterogeneous mixtures do not have uniform composition; samples differ throughout.
- Common examples: oil and water, sand, fog (liquid + gas), smog (solid + gas).
- Homogeneous solutions have uniform composition; elements/compounds are evenly mixed.
- Liquid solutions: solute dissolved in solvent (e.g., salt water).
- Solid solutions: metal alloys (e.g., copper mixed with gold or silver).
- Gas solutions: mixed gases like air (nitrogen and oxygen) always mix homogeneously.
Separation of Mixtures and Solutions
- Mixtures and solutions can be separated by physical means (e.g., evaporation, condensation, filtration, using magnets).
Pure Substances
- Homogeneous pure substance element: single type of element, same atoms (e.g., molybdenum, neon, cesium).
- Homogeneous pure substance compound: chemically combined elements, represented with a chemical formula (e.g., NaCl for sodium chloride, C6H12O6 for sucrose).
Identifying Compounds
- Use chemical formulas to identify compounds; subscripts show the number of atoms (e.g., C6H12O6 has 6 carbons, 12 hydrogens, 6 oxygens).
- Compounds can be modeled by molecular shapes or formulas.
Key Terms & Definitions
- Heterogeneous mixture — a physical combination with non-uniform composition.
- Homogeneous solution — a physical combination with uniform composition.
- Element — a pure substance made of one type of atom.
- Compound — a pure substance with two or more different elements chemically combined.
- Solute — the substance dissolved in a solution.
- Solvent — the substance that dissolves the solute.
Action Items / Next Steps
- Practice classifying materials into the four categories.
- Be able to identify elements, compounds, mixtures, and solutions using examples and chemical formulas.