Mass number number of protons in a nucleus, and thus uniquely identifies an element. Hence, the difference between the mass number and the atomic number gives the number of neutrons ("N") in a given nucleus: . The mass number is written either after the element name or as a superscript to the left of an element's symbol. For example, the most common isotope of carbon is carbon-12, or , which has 6 protons and 6 neutrons. The full isotope symbol would also have the atomic number ("Z") as a subscript to the left of the element symbol directly below the mass number:
Isotopes of flerovium Isotopes of flerovium Flerovium (Fl) 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 Fl in 1999 (or possibly 1998). Flerovium has seven known isotopes, and possibly 2 nuclear isomers. The longest-lived isotope is Fl with a half-life of 1.9 seconds, but the unconfirmed Fl may have a longer half-life of 19 seconds. The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 114. "This section deals