| Pure Substances | Mixtures | ||
| Elements | Compounds | Mixtures | |
| Macroscopic Level | Elements look like one pure substance; e.g. a chunk of gold (Au). | Compounds look like one pure substance; e.g. a quartz crystal (SiO2) | Mixtures if homogeneous may look like one pure substance, but are not; e.g. milk, steel. If heterogeneous you can see the constituents; you may need some optical aid to see them, e.g. cells in a plant. |
| Particulate Level | Elements may be free (He, Ar) or bound to each other, as in H2, O2, N2, or C60 buckyballs. | Compounds are made from two or more different elements, as in HCl or H2SO4 | Mixtures have elements or compounds sitting or swimming around next to each other as in gold dust in an ore, sugar dissolved in water, or the oxygen and nitrogen in the air. |
| Separation | Bonded elements (e.g. H2) can be separated by chemical means. | Compounds can be broken into their elements by chemical means. | Mixtures can be separated by physical means. Examples: distillation, chromatography, preferential dissolving (e.g. sugar and sand with water). |