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There are 20 isotopes of fermium listed in NUBASE 2016, [15] with atomic weights of 241 to 260, [b] of which 257 Fm is the longest-lived with a half-life of 100.5 days. 253 Fm has a half-life of 3 days, while 251 Fm of 5.3 h, 252 Fm of 25.4 h, 254 Fm of 3.2 h, 255 Fm of 20.1 h, and 256 Fm of 2.6 hours.
This is a list of radioactive nuclides (sometimes also called isotopes), ordered by half-life from shortest to longest, in seconds, minutes, hours, days and years. Current methods make it difficult to measure half-lives between approximately 10 −19 and 10 −10 seconds.
There are 20 known radioisotopes ranging in atomic mass from 241 Fm to 260 Fm (260 Fm is unconfirmed), and 4 nuclear isomers, 247m Fm, 250m Fm, 251m Fm, and 253m Fm. The longest-lived isotope is 257 Fm with a half-life of 100.5 days, and the longest-lived isomer is 247m Fm with a half-life of 5.1 seconds.
A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z). [ 1 ] The definitive visualisation of all 118 elements is the periodic table of the elements , whose history along the principles of the periodic law was one of the founding ...
This is a list of chemical elements and their atomic properties, ordered by atomic number (Z).. Since valence electrons are not clearly defined for the d-block and f-block elements, there not being a clear point at which further ionisation becomes unprofitable, a purely formal definition as number of electrons in the outermost shell has been used.
The stability of nuclei decreases greatly with the increase in atomic number after curium, element 96, so that all isotopes with an atomic number above 101 decay radioactively with a half-life under a day. No elements with atomic numbers above 82 (after lead) have stable isotopes. [107]
Phosphorus is a chemical element with the symbol P and the atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus , but because it is highly reactive , phosphorus is never found as a free element on Earth.
Proton number Z, also named the atomic number, determines the position of an element in the periodic table. The approximately 3300 known nuclides [7] are commonly represented in a chart with Z and N for its axes and the half-life for radioactive decay indicated for each unstable nuclide (see figure). [8]