Elements, Compounds, and Mixtures
The fundamental classification of all matter — know definitions and distinguishing features precisely.
| Type | Definition | Separation | Example |
|---|---|---|---|
| Element | One type of atom only | Cannot be broken down chemically | Fe, O₂, Cu, N₂ |
| Compound | Two+ elements chemically bonded in fixed ratio | Chemical methods only | H₂O, NaCl, CO₂, CuSO₄ |
| Mixture | Two+ substances physically combined (no fixed ratio) | Physical methods (filtration, distillation) | Salt water, air, crude oil, alloys |
Compound vs Mixture — key distinctions:
| Feature | Compound | Mixture |
|---|---|---|
| Ratio of components | Fixed (by chemical formula) | Variable |
| Formation | Requires chemical reaction | Physical mixing only |
| Properties | Different from elements | Components retain own properties |
| Separation | Only by chemical methods | Physical methods (distillation, filtration, etc.) |
| Energy change | Yes (bonds formed/broken) | No (usually) |
Example: Iron + sulfur mixture vs iron sulfide compound.
- Mixture of Fe + S: iron filings can be removed by magnet; sulfur dissolves in CS₂; each element keeps its properties.
- Iron(II) sulfide (FeS): cannot be separated by magnet; has different properties from iron or sulfur alone; requires chemical reaction to form.
- Element: one atom type. Compound: elements chemically combined (fixed ratio). Mixture: physically combined (variable ratio).
- Compounds have different properties from their elements. Mixture components keep their properties.
- Mixtures separated by physical methods; compounds only by chemical reactions.