Mixture vs Compound
A mixture is a physical combination of two or more substances that keep their own properties — you can usually separate them by physical means. A compound is a chemical combination of elements in a fixed ratio, held together by chemical bonds, with properties unlike either of the original elements. Salt water is a mixture; salt itself is a compound.
Last reviewed on 2026-04-27.
Quick Comparison
| Aspect | Mixture | Compound |
|---|---|---|
| How combined | Physically — components keep identity | Chemically — atoms bond into new substance |
| Component ratio | Variable — any proportion | Fixed — defined by chemical formula |
| Separation | Physical methods (filtering, distilling, evaporation) | Chemical reactions only |
| Properties | Average of components, sometimes new | Different from either element |
| Energy change | Usually little or none | Chemical bond formation releases or absorbs energy |
| Examples | Air, salt water, alloys, sand and iron filings | Water, salt, glucose, carbon dioxide |
| Types | Homogeneous (uniform) and heterogeneous | Ionic, covalent, metallic compounds |
Key Differences
1. How they're put together
Mixtures combine substances physically. The components are mixed in but each one retains its molecular identity. Air is nitrogen, oxygen, argon, and others — each gas is still itself; they're just sharing space.
Compounds combine elements chemically. Atoms form bonds, sharing or transferring electrons, and the result is a new substance. Water (H2O) isn't hydrogen and oxygen mingling — it's atoms bonded into a new molecule with very different properties.
2. Ratios
Mixtures can have any composition. Salt water can be 1% salt or 30% salt; both are still salt water.
Compounds have fixed ratios. Water is always 2 hydrogen atoms per oxygen. Sodium chloride is always one Na⁺ per Cl⁻. The ratios are dictated by chemistry, not choice.
3. Separation
Mixtures can be separated physically. Filter sand from water, distil alcohol from water, magnetise iron filings out of sand, evaporate salt from solution.
Compounds require chemical reactions to break apart. Splitting water into hydrogen and oxygen needs electricity (electrolysis); decomposing salt back into sodium and chlorine needs molten-state electrolysis. You can't separate water into H and O by filtering, settling, or evaporating.
4. Properties
Mixture properties are usually some kind of average or combination of the components. Salt water is salty; iron filings in sand still rust.
Compound properties are typically very different from the elements they're built from. Sodium is a soft, reactive metal; chlorine is a poisonous green gas; combined chemically, they make table salt — a stable, edible white crystal.
5. Subtypes
Mixtures are homogeneous (uniform throughout — like salt water or air) or heterogeneous (visibly different parts — like a salad, sand and pebbles, or oil and water).
Compounds classify by bond type: ionic (transferred electrons, like NaCl), covalent (shared electrons, like water and CO2), or metallic (a sea of electrons in metals' alloys, though metals themselves are elements).
6. Energy involvement
Mixing usually involves little energy change. Stirring sugar into tea cools the tea slightly because the dissolution is mildly endothermic, but no significant chemistry happens.
Forming or breaking a compound involves the energy of chemical bonds — sometimes substantial. Burning hydrogen in oxygen releases enough energy to power a rocket; breaking water back into H and O requires putting that energy back in.
When to Choose Each
Choose Mixture if:
- Discussing solutions, alloys, suspensions, smokes, and many everyday materials.
- Cooking — most foods are mixtures of compounds and other mixtures.
- Anywhere components retain their original chemical identities.
Choose Compound if:
- Discussing pure chemicals: water, salt, sugar, glucose, methane.
- Stoichiometry — chemical equations balance because compounds have fixed ratios.
- Anywhere a substance has properties distinct from its elemental constituents.
Worked example
A glass of seawater is a mixture: water (a compound) plus dissolved sodium chloride (a compound) plus other dissolved substances. Boil it, and you can recover pure water vapour and leave the salt behind — physical separation. Inside that salt, the sodium and chlorine are bonded into a compound; recovering elemental sodium and elemental chlorine requires running an electric current through molten salt — a chemical change.
Common Mistakes
- "All mixtures are uniform." Many are heterogeneous — a salad is a mixture, but you can pick out the components.
- "Compounds are mixtures of elements." They're chemical combinations, not physical mixes. Water is not just hydrogen and oxygen sitting together.
- "Air is a compound." Air is a mixture — nitrogen, oxygen, argon, CO2, and others. Each is its own molecule; they share space.
- "You can always tell mixtures from compounds at a glance." Solutions look uniform; only chemistry can confirm whether components are bonded or just mingling.