2.1 Elements, compounds and mixtures
- Syllabus
- 0620–2026–2027
- Topic
- 2.1
- Level
- —
Learning objectives
Distinguish elements, compounds and mixtures
Elements, compounds and mixtures differ by what particles they contain, whether different elements are chemically bonded and whether the composition is fixed.
| Type of substance | Particle and composition description | How it can be separated |
|---|---|---|
| element | one type of atom; all atoms have the same proton number | cannot be broken into simpler substances by chemical means |
| compound | atoms of two or more elements chemically bonded in a fixed ratio | separated into elements only by chemical reactions |
| mixture | two or more substances together but not chemically bonded; proportions can vary | components can be separated by physical methods |
A compound is a new pure substance with properties different from its elements. In a mixture, each component keeps its chemical identity and no single formula describes the whole mixture.
In a particle diagram, an element contains only one atom symbol, even if its atoms are paired. A compound has particles containing different atom symbols bonded together in the same pattern. A mixture shows more than one kind of particle.
A molecule containing two identical atoms is still an element, not a compound. A pure compound can contain many particles but is not a mixture because every particle has the same fixed composition.