Element of the day: Bismuth
Unoxidized, synthetic bismuth crystals. A high purity (99.99%) 1 cubic centimeter bismuth cube is shown on the top left for comparison.
Original image is provided by the own work of Alchemist-HP.
Discovery and History of Bismuth
As one moves across the sixth row of the periodic table, there are three toxic heavy metals: mercury, thallium, and lead. On the right side of this row, there are the dangerously radioactive elements polonium, astatine, and radon. Sandwiched right in between, sitting at the 83rd spot of the periodic table, is relatively safe bismuth (Bi). It is one of the first metals to have ever been discovered, with its discovery dating back to the early 15th century by an unknown practitioner of alchemy. Bismuth metals may have even been used since ancient times, but it is very probable that it was confused for other metals like lead and tin since they share similar physical properties.
Oxidized, iridescent bismuth crystals due to exposure of the metal’s surface to air.
Bismuth is about twice as abundant as gold in the Earth’s crust. It is a brittle metal that looks like silver with a faint pink tinge. Exposing bismuth to air causes it to oxidize and form an iridescent film over the element’s exposed surface that exhibits many different colors.
Bismuth was historically considered to be the element with the highest atomic mass that is stable, but a study in 2003 discovered that its atoms do radioactively decay into thallium; however, this decay is extremely slow since the half-life of bismuth is over a billion times longer than the current age of the universe. Recall that half-life is the time taken for an amount of radioactive product to decrease to half its original value. Due to this extraordinarily long half-life, bismuth is considered stable for nearly all purposes.
Applications of Bismuth
Putting the Bismuth in Pepto-Bismol
1957 Life magazine advertisement for Pepto-Bismol. It was first sold in 1900 by a physician in New York as a remedy for infant diarrhea.
Since the 1700s, bismuth has been used in treating stomach complaints like peptic ulcers and diarrhea. Given its location on the periodic table right in between the highly toxic lead and poisonous polonium, this is quite surprising. Bismuth subsalicylate, also known by its brand name Pepto-Bismol, is medication that most of us have probably taken to combat diarrhea, indigestion, heartburn, and nausea. This medication is a derivative of the compound salicylic acid (commonly found in aspirin) to product anti-inflammatory effects. Pepto-Bismol is 57% bismuth by weight, and this bismuth has bactericidal properties since small amounts of heavy metals like bismuth can be toxic to bacteria.
Nontoxic Lead Replacement
One of bismuth’s many applications is as a replacement to lead since it is relatively non-toxic and weighs 86% as much as lead. This difference in mass is small enough that it can be used as a substitute for lead in creating ammunition and fishing sinkers. This has the potential to significantly decrease toxicity that lead imparts on the environment.
Comparison of the toxic lead chromate (left) and cadmium sulfide yellow (center) powders with the nontoxic bismuth vanadate (right) that is commonly used by artists. Although there are subtle differences in hue between the three compounds, their toxicities are significantly different.
Cosmetics and Pigments
Another one of bismuth’s applications is in cosmetics and painting pigments. Bismuth oxychloride, for instance, is used to produce a pearlescent finish of some white nail varnishes. It is also used as paint for eye shadows and in hair sprays. Another example is bismuth vanadate, which is used as a light-stable, non-reactive yellow paint pigment that is used in artists’ paint. This replaced the significantly more toxic lead chromate and cadmium sulfide yellow and orange-yellow pigments previously used. Evidently, bismuth has proven to be a viable and relatively nontoxic substitute in across different fields and disciplines.
