Pure Substances
- A pure substance is made up of only one kind of particle (atoms or molecules).
- It has uniform composition and definite properties throughout.
- Cannot be separated into simpler substances by physical methods.
- Two types:
- Elements → made of one kind of atom (e.g., gold, oxygen, hydrogen).
- Compounds → made of two or more elements chemically combined in a fixed ratio (e.g., water (H₂O), salt (NaCl), carbon dioxide (CO₂)).
- Examples: Iron, pure sugar, distilled water, oxygen gas.
Mixtures
- A mixture is made up of two or more substances physically combined (not chemically bonded).
- The substances retain their individual properties.
- Can be separated by physical methods (like filtration, evaporation, or distillation).
- Two types:
- Homogeneous Mixtures → uniform composition throughout (e.g., salt dissolved in water, air, lemonade).
- Heterogeneous Mixtures → non-uniform composition, substances can be seen separately (e.g., sand in water, salad, oil and water).
- Examples: Air, soil, sugar in tea, milk.
Key Difference:
- Pure substance = single type of particle, fixed composition (cannot be separated physically).
- Mixture = combination of substances, variable composition (can be separated physically).