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
Dense set close to it (see Diophantine approximation). Formally, a subset "A" of a topological space "X" is dense in X if for any point "x" in "X", any neighborhood of "x" contains at least one point from "A" (i.e., "A" has non-empty intersection with every non-empty open subset of "X"). Equivalently, "A" is dense in "X" if and only if the only closed subset of "X" containing "A" is "X" itself. This can also be expressed by saying that the closure of "A" is "X", or that the interior of the complement of "A" is empty. The density of a topological