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Abrasion     Rocks bang into each other and become smaller and more rounded.

Acid rain     All rainfall is slightly acidic because of the dissolved carbon dioxide. The term acid rainrefers to rain that is extra acidic because of large amounts of dissolved gases such as nitrogen oxides and sulfur oxides. These can make nitric acid and sulfuric acid as well as many others.

Addition reaction     A substance is reacted with an alkene to form a compound with a single bond between the two formerly double bonded carbon atoms. An example is the decolourisation of bromine.

Addition polymerisation     One long single molecule is made from many short chain monomers. All the starting material is incorporated in the final polymer. An addition reaction taks place each time the chain is extended.

Air     The mixture of gases which we breathe! Most of the air (almost 4/5) is nitrogen with oxygen making up 1/5 and small amounts of argon (1%) and other gases in even smaller amounts. Carbon dioxide is only present in very small quantities. Water vapour is present in varying amounts depending on where you are in the world.

Air pollution     Substances that have been released into the air that are not natural. In the past, people have not been very concerned about waste being put into the atmosphere. Many thought that a tall chimney would remove the problem. Nowadays we are much more careful and take more care to dispose of problem gases, smoke and dusts in a more responsible way.

Alkane     A hydrocarbon that has only single bonds. It is a saturated hydrocarbon.

Alloy     A mixture of different metals. Bronze, brass, duralumin are some typical examples of alloys.

Atom     The smallest particle tha can be recognised as being an element. If you break an atom into its smaller pieces (protons, neutrons and electrons) you can no longer identify a particular element.

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