Isotopes of lithium

Naturally occurring lithium (₃Li, standard atomic weight: [6.938, 6.997], conventional: 6.94) is composed of two stable isotopes, lithium-6 and lithium-7, with the latter being far more abundant: about 92.5 percent of the atoms. Both of the natural isotopes have an unexpectedly low nuclear binding energy per nucleon (~5.3 MeV) when compared with the adjacent lighter and heavier elements, helium (~7.1 MeV) and beryllium (~6.5 MeV). The longest-lived radioisotope of lithium is lithium-8, which has a half-life of just 838 milliseconds. Lithium-9 has a half-life of 178 milliseconds, and lithium-11 has a half-life of about 8.6 milliseconds. All of the remaining isotopes of lithium have half-lives that are shorter than 10 nanoseconds. The shortest-lived known isotope of lithium is lithium-4, which decays by proton emission with a half-life of about 6977909999999999999♠9.1×10⁻²³ seconds, although the half-life of lithium-3 is yet to be determined, and is likely to be much shorter.

Lithium-7 and lithium-6 are two of the primordial nuclides that were produced in the Big Bang, with lithium-7 to be 10⁻⁹ of all primordial nuclides and amount of lithium-6 around 10⁻¹³. A small percentage of lithium-6 is also known to be produced by nuclear reactions in certain stars. The isotopes of lithium separate somewhat during a variety of geological processes, including mineral formation (chemical precipitation and ion exchange). Lithium ions replace magnesium or iron in certain octahedral locations in clays, and lithium-6 is sometimes preferred over lithium-7. This results in some enrichment of lithium-7 in geological processes.