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Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells.

In this CCEA study guide, you can revise and learn the atomic structure of chlorine, the structure of the nucleus, and the structure of an atom. Remember that atoms are made up of protons, neutrons and electrons. Change the number of neutrons in an atom and it becomes an isotope, change the number of electrons, it becomes an ion.

Radioactivity was first noticed by French physicist, Henri Becquerel, in 1896, when he observed that some photographic plates which had been stored close to a uranium compound had become partly exposed or ‘fogged’.

People are exposed to sources of radiation in all aspects of everyday life. Radioactive sources can be very useful but need handling carefully to ensure safety.

Nuclear fission is the splitting of a large atomic nucleus such as uranium into smaller nuclei with the release of energy.

Nuclear fusion occurs when two small, light nuclei join together to make one heavier nucleus. The nuclei fuse together, and energy is released.