Naturally occurring lithium (₃Li) is composed of two stable isotopes, lithium-6 (⁶Li) and lithium-7 (⁷Li), with the latter being far more abundant on Earth. Radioisotopes are short-lived: the particle-bound ones, ⁸Li, ⁹Li, and ¹¹Li, have half-lives of 838.7, 178.2, and 8.75 milliseconds respectively.

Both of the natural isotopes have anomalously low nuclear binding energy