Which elements are unstable and radioactive

An unstable atom has excess internal energy, with the result that the nucleus can undergo a spontaneous change towards a more stable form. This is called 'radioactive decay'. Each element exists in the form of atoms with several different sized nuclei, called isotopes.

Unstable isotopes which are thus radioactive are called radioisotopes. Some elements, eg uranium, have no stable isotopes. When an atom of a radioisotope decays, it gives off some of its excess energy as radiation in the form of gamma rays or fast-moving sub-atomic particles. For example carbon, carbon is stable and has six protons and six neutrons. However as the number of protons increases, more neutrons are needed to keep the nucleus stable.

For example lead, lead has 82 protons and has neutrons. Nuclei with too many, or too few, neutrons do exist naturally but are unstable and will disintegrate or decay by emitting radiation. The band of stability is the range of stable nuclei on a graph that plots the number of neutrons in a nuclide against the number of protons. Known stable nuclides are shown with individual blue dots, while the and 1. It should be noted that just because a nucleus is "unstable" able to undergo spontaneous radioactive decay does not mean that it will rapidly decompose.

Allison Soult , Ph. Department of Chemistry, University of Kentucky. Learning Outcomes Recognize that radioactivity is a signature of unstable nuclide - radioisotopes. But quality journalism comes at a price. Support the next century of science journalism. Skip to content. Science News Needs You Support nonprofit journalism. By Carmen Drahl March 1, at pm. Tap or click to expand.

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