Period 2 element two make up all natural occurrence of lithium on Earth, although further isotopes have been synthesized. In ionic compounds, lithium loses an electron to become positively charged, forming the cation Li. Lithium is the first alkali metal in the periodic table, and the first metal of any kind in the periodic table. At standard temperature and pressure, lithium is a soft, silver-white, highly reactive metal. With a density of 0.564 g·cm, lithium is the lightest metal and the least dense solid element. Lithium is one of the few elements synthesized in the Big Bang, making it a primordial element. Lithium
E-dense semigroup introduced by Gabriel Thierrin in 1955. Some authors use "E"-dense to refer only to "E"-inversive semigroups in which the idempotents commute. More generally, a subsemigroup "T" of "S" is said dense in "S" if, for all "x" ∈ "S", there exists "y" ∈ "S" such that both "xy" ∈ "T" and "yx" ∈ "T". A semigroup with zero is said to be an "E"*-dense semigroup if every element other than the zero has at least one non-zero weak inverse. Semigroups in this class have also been called 0-inversive semigroups. E-dense semigroup In abstract algebra, an E"-dense semigroup (also called an