Elements, compounds and mixtures

• Element


  A pure substance that is listed in 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.
• 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 filtering and distillation.
• Air is a mixture that contains the elements nitrogen, oxygen and argon, and also the compound carbon dioxide.
• Filtering


  The 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'.
• Distillation


  A separation technique which involves a solution being heated so that the solvent evaporates before being cooled to form a pure liquid.