The metallic element, Bi, of atomic number 83 and atomic weight 208.980 belonging in the periodic table to group 15. Bismuth is the most metallic element in this group in both physical and chemical properties. The only stable isotope is that of mass 209. It is estimated that the Earth's crust contains about 0.00002% bismuth. It occurs in nature as the free metal and in ores. The principal ore deposits are in South America. However, the primary source of bismuth in the United States is as a by-product in refining of copper and lead ores.
The main use of bismuth is in the manufacture of low-melting alloys which are used in fusible elements in automatic sprinklers, special solders, safety plugs in compressed gas cylinders, and automatic shutoffs for gas and electric water-heating systems. Some bismuth alloys, which expand on freezing, are used in castings and in type metal. Another important use of bismuth is in the manufacture of pharmaceutical compounds.
Bismuth is a gray-white, lustrous, hard, brittle, coarsely crystalline metal. It is one of the few metals which expand on solidification. The thermal conductivity of bismuth is lower than that of any metal, with the exception of mercury. The table cites the chief physical and mechanical properties of bismuth. Bismuth is inert in dry air at room temperature, although it oxidizes slightly in moist air. It rapidly forms an oxide film at temperatures above its melting point, and it burns at red heat, forming the yellow oxide, Bi₂O₃. The metal combines directly with halogens and with sulfur, selenium, and tellurium; however, it does not combine directly with nitrogen or phosphorus. Bismuth is not attacked at ordinary temperatures by air-free water, but it is slowly oxidized at red heat by water vapor.
Almost all compounds of bismuth contain trivalent bismuth. However, bismuth can occasionally be pentavalent or monovalent. Sodium bismuthate and bismuth pentafluoride are perhaps the most important compounds of Bi(V). The former is a powerful oxidizing agent, and the latter a useful fluorinating agent for organic compounds .