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 non-empty subset of a set "X" equipped with the trivial topology is dense, and every topology for which every non-empty subset is dense must be trivial. Denseness is transitive: Given three subsets "A", "B" and "C" of a topological space "X" with such that "A" is dense in "B" and "B" is dense in "C" (in the respective subspace topology) then "A" is also dense in "C". The image of a dense subset under a surjective continuous function is again dense. The density of a topological space (the least of the cardinalities of its dense subsets) is a topological invariant.