The chemical elements beyond lead are radioactive, and they do not have stable isotopes. This means that they will decay into other elements. As their atomic number (the number of protons in their nucleus) increases, the time it takes for them to decay tends to get shorter, going from billions of years to less than one millisecond. There is a theory in physics that says that after a number of elements with short half lives, there will be others with longer half lives. These are generally known as "islands of stability". These elements are expected to have isotopes that decay in several minutes.The theory is that, similarly to electron shells, the nucleus of an atom is made of "shells" (which can be thought of as layers of protons and neutrons), and that when a nucleus has entirely filled shells, it is significantly more stable.
A filled shell would have "magic numbers" of neutrons and protons, known magic numbers are 2, 8, 20, 28, 50, 82, and 126; however, further numbers are predicted to exist. One element that is predicted to be quite stable is unbihexium, in particular, its isotope unbihexium-310, which would be "doubly magic" (both its atomic number of 126 and neutron number of 184 are thought to be magic) and so would be the most likely to be very stable. The next lightest doubly magic isotope of an element is lead-208, the heaviest stable isotope of any element and the most stable heavy metal.
Isotopes have been produced with enough protons to put them on an island of stability but with too few neutrons. It is possible that these elements possess unusual properties and, if they have isotopes with long enough lifespans, would be available for various uses (such as particle accelerator targets and neutron sources).
References[change | change source]
- "Shell Model of Nucleus". HyperPhysics. Department of Physics and Astronomy, Georgia State University. Retrieved 22 January 2007.