Standard atomic weight real life substances—for example, in pharmaceuticals and scientific research. Atomic weights are specific to single sources and samples of an element, such as the atomic weight of carbon in a particular bone from a particular archeological site. Standard atomic weight generalizes such values to the "range of atomic weights" which a chemist might expect to derive from many random samples from Earth. This range is the cause of the "interval notation" in some standard atomic weight values. Out of the 118 known chemical elements, 84 are stable and have this Earth-environment based value. Typically, such a value is, for example
Isotopes of hassium Isotopes of hassium Hassium (Hs) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was Hs in 1984. There are 12 known isotopes from Hs to Hs and 1–4 isomers. The longest-lived isotope is Hs with a half-life of 10 seconds. Super-heavy elements such as hassium are produced by bombarding lighter elements in particle accelerators that induce fusion reactions. Whereas most of the isotopes of hassium can be synthesized directly this way, some heavier ones have only been observed as decay