Overview
This lecture covers the classification of matter, distinguishing elements and compounds, mixtures (homogeneous and heterogeneous), the three main states of matter, and differentiates between physical and chemical properties and changes.
Elements vs. Compounds
- An element consists of one type of atom and cannot be broken down chemically (e.g., helium, sulfur, mercury, iron).
- A compound contains two or more different elements chemically combined (e.g., sugar, sodium hydroxide, potassium chloride).
- Compounds can be broken down into simpler substances by chemical means.
Pure Substances vs. Mixtures
- Pure substances have uniform composition and include both elements and compounds (e.g., iron nail, propane gas, potassium chloride sample).
- Mixtures contain two or more substances physically combined and can be separated physically (e.g., soft drink, cheese sandwich, salt substitute).
- Mixtures can be homogeneous (uniform throughout, e.g., non-fat milk, cranberry juice) or heterogeneous (components visible, e.g., chocolate chip ice cream, peanut butter sandwich).
States of Matter
- Three main states are solid, liquid, and gas (plasma is a fourth, less discussed).
- Solids have definite shape and volume.
- Liquids have definite volume but take the shape of their container.
- Gases have neither definite shape nor definite volume and expand to fill their container.
Physical vs. Chemical Properties and Changes
- Physical properties: describe without changing substance identity (e.g., color, phase, shape, smell, melting, phase changes).
- Chemical properties: involve a substance's ability to undergo chemical change (e.g., ability to react, tarnishing, burning).
- Physical changes: alter form or appearance but not identity (e.g., melting, cutting, compressing gas).
- Chemical changes: result in new substances (e.g., burning, rusting, digestion, apples browning).
Key Terms & Definitions
- Element — Pure substance with one type of atom; cannot be chemically broken down.
- Compound — Pure substance with two or more elements chemically combined.
- Mixture — Physical blend of two or more substances, not chemically combined.
- Homogeneous mixture — Mixture that looks uniform throughout.
- Heterogeneous mixture — Mixture where components are visibly different.
- Physical property — Characteristic observed without changing substance identity.
- Chemical property — Characteristic revealed when substance undergoes chemical change.
Action Items / Next Steps
- Review the flow chart for classifying matter provided by the instructor.
- Read related textbook sections on elements, compounds, mixtures, and properties of matter.
- Practice classifying everyday materials as elements, compounds, or mixtures and as physical/chemical changes.