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Isotopes of nobelium 54 s activity was actually due to No and the isotope No was retracted. Isotopes of nobelium Nobelium (No) 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 (and correctly identified) was No in 1966. There are 12 known radioisotopes, which are No to No and No, and 3 isomers, No, No, and No. The longest-lived isotope is No with a half-life of 58 minutes. The longest-lived isomer is No with a half-life of 1.7 seconds. This cold fusion reaction was