- Bismuth (Bi) is a post-transition metal with atomic number 83, located in Group 15 of the periodic table, alongside nitrogen, phosphorus, arsenic, and antimony.
- Its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³, giving it five valence electrons. Bismuth commonly exhibits oxidation states of +3 and, less commonly, +5, though the +3 state is far more stable due to the inert pair effect. Each atom of bismuth contains eighty-three protons, eighty-three electrons, and about 126 neutrons in its most stable isotope, bismuth-209 (²⁰⁹Bi).
- Bismuth has been known since ancient times but was often confused with lead, tin, or antimony due to its similar appearance. It was first clearly distinguished as a unique element in the 15th century by German scientist Basil Valentine and later by Georgius Agricola in the 16th century. The name bismuth likely comes from the German word Wismut, meaning “white mass.”
- Physically, bismuth is a brittle, crystalline metal with a silvery-white color and often shows iridescent hues of pink, purple, and blue on its oxidized surface. It has a relatively low density for a heavy metal (9.78 g/cm³), a melting point of 271 °C (520 °F), and a boiling point of 1,564 °C (2,847 °F). Bismuth is notable for having one of the lowest thermal conductivities among metals and a very high electrical resistivity. Unlike most metals, it expands when it solidifies, a property it shares with water and antimony.
- Chemically, bismuth is relatively stable and resistant to oxidation. It forms compounds in both the +3 and +5 oxidation states, though bismuth(III) compounds, such as bismuth(III) oxide (Bi₂O₃), are more common and stable. Bismuth compounds often display low toxicity compared to neighboring heavy metals. This unusual property makes bismuth useful in medical and cosmetic applications where lead or mercury would be harmful.
- Bismuth has a variety of modern applications. It is widely used in pharmaceuticals, particularly in bismuth subsalicylate (C₇H₅BiO₄), the active ingredient in common antacid and anti-diarrheal medicines. In metallurgy, bismuth is used to create low-melting alloys for fire detection and suppression systems, as well as in solders that replace toxic lead-based versions. Its unique expansion upon solidification makes it valuable in casting processes. Bismuth compounds are also used in cosmetics, pigments, and as catalysts in organic chemistry.
- In electronics and materials science, bismuth has attracted interest for its semiconducting properties and thermoelectric applications. Bismuth telluride (Bi₂Te₃), for example, is a leading thermoelectric material used to convert heat into electricity and vice versa.
- Biologically, bismuth is considered the least toxic of the heavy metals, and certain compounds are even beneficial in medicine. However, excessive exposure can still cause harm, leading to symptoms such as kidney or liver damage, though such cases are rare compared to other heavy metals.
- Environmentally, bismuth is relatively rare, making up about 0.00002% of Earth’s crust. It is usually found in association with lead, copper, silver, and tin ores. Commercial production of bismuth is largely as a by-product of lead, copper, and tin smelting. Major producers include China, Mexico, and Peru. Because it is both rare and comparatively safe, bismuth has become increasingly valuable as a replacement for lead in environmentally friendly applications.
