Bismuth

Bismuth is a metal (ore) with chemical symbol Bi and atomic number (proton number) 83. It is one of the elements in group 15 of the periodic table, alongside antimony and arsenic. Its colour is silvery-white and sometimes has a lustrous reddish tinge when a thin oxide layer forms on its surface.

Bismuth is a brittle metal that breaks easily. It is known for unusual physical properties: when it cools and solidifies, it expands and increases in volume, which is unlike most metals. It also has low electrical and thermal conductivity compared to other metals, and strong diamagnetism.

Physical and chemical properties

Bismuth has a relatively low melting point compared to other heavy metals—approximately 271 degrees Celsius—whereas its boiling point is very high. Its density is around 9.8 g/cm³. Naturally crystalline bismuth, when cooled in an orderly fashion, displays various colours in a geometric pattern, due to a thin oxide layer that refracts light.

Bismuth chemistry typically occurs in oxidation states of +3 and, less commonly, +5. Its common compounds include bismuth oxide and bismuth subsalicylate. The most abundant isotope, bismuth-209, was long considered stable; later experiments showed it decays very slowly (radioactive), but its half-life is so long that for practical purposes it is considered stable.

Occurrence and production

Bismuth is not abundant in the Earth's crust. It is found in specific ores such as bismuthinite (bismuth sulfide) and bismite, but is mostly obtained as a by-product when refining lead, copper, tin and tungsten. China is among the leading producers.

Uses

Because of its low toxicity compared to lead, bismuth is used as a substitute for certain heavy metals that are hazardous: fishing weights, water pipe fittings, and pigments. Bismuth alloys have lower melting points, making them suitable for soldering, fire sprinkler systems and electrical fuses. In medicine, bismuth subsalicylate is used for stomach and intestinal complaints; some compounds are used to treat infections caused by the bacterium Helicobacter pylori.