Elements, compounds and mixtures
Element
- A pure substance that is listed in the periodic tableA tabular representation of all known elements in order based on atomic number, eg all the noble gases are found on the right of the periodic table. and only has one type of atom in it.
- There are over 100 elements.
- Most are metals, a few are metalloids (also known as semi-metals), and the rest are non-metals.
Compound
- A pure substance made from more than one type of element chemically bonded together.
- Elements bond in fixed ratios and so can be represented by a chemical formula. For example, sodium chloride has the same number of sodium ions and chloride ions, so its formula is NaCl, whereas water is always made from twice the number of hydrogen atoms as oxygen atoms, so it is H2O.
Mixture
- An impure substance made from different elements or compounds mixed together that are not chemically joined.
- Mixtures can usually be separated by physical techniques such as filteringThe process of passing a mixture through a device - soluble substances pass through the filter as a 'filtrate' but insoluble substances or unwanted material will stay in the filter as a 'residue'. and distillationA separation technique which involves a solution being heated so that the solvent evaporates before being cooled to form a pure liquid..
- Air is a mixture that contains the elements nitrogen, oxygen and argon, and also the compound carbon dioxide.