Fermium (100Fm) is a synthetic element, meaning it does not possess any stable isotopes. Because of this, it is impossible to assign a standard atomic weight to the element. All isotopes of fermium are artificial and must be produced in laboratory settings.
The history of its isotopes began in 1952 with the discovery of 255Fm. Shortly after this initial discovery, the isotope 250Fm was also synthesized independently, marking the early stages of research into the various forms of this element.