Bismuth
Bismuth is a chemical element with the symbol Bi and atomic number 83, classified as a pentavalent post-transition metal in group 15 of the periodic table.[1] It manifests as a lustrous, silvery-white crystalline solid with a faint pinkish tinge, notable for forming iridescent oxide layers that produce rainbow-like colors due to thin-film interference.[2] Bismuth exhibits the highest diamagnetism of any element, repelling magnetic fields strongly, and possesses one of the lowest thermal conductivities among metals, alongside a unique expansion upon solidification akin to water.[2][3] Although utilized since ancient times in alloys and cosmetics, bismuth was formally distinguished as a unique element from lead and tin by French chemist Claude François Geoffroy in 1753 through chemical analysis confirming its distinct properties.[4] It occurs sparingly in Earth's crust at about 0.02 parts per million, primarily as a byproduct of refining copper, lead, and tin ores, with principal mineral sources including bismuthinite (Bi₂S₃) and bismite (Bi₂O₃).[4] Despite its position low in the periodic table suggesting potential radioactivity, naturally occurring bismuth is overwhelmingly stable isotope bismuth-209, with only rare alpha decay observed.[3] Bismuth's low toxicity relative to heavy metals like lead enables its use as a non-toxic alternative in applications such as fishing weights, shotgun pellets, and low-melt solders, reducing environmental lead contamination.[5] In medicine, bismuth compounds like bismuth subsalicylate provide antimicrobial and protective effects for gastrointestinal treatments, including relief from diarrhea and indigestion.[5] Additionally, bismuth features in specialized alloys for castings and thermoelectric devices, leveraging its expansion on cooling to minimize shrinkage defects, and in emerging high-temperature superconductors.[4]Properties
Physical properties
Bismuth is a brittle, post-transition metal exhibiting a silvery-white luster when freshly prepared, which quickly forms a thin oxide layer producing an iridescent tarnish of rainbow hues.[6] This oxide layer contributes to its distinctive appearance, and under controlled cooling conditions, bismuth forms hopper crystals with stepped, pyramidal structures due to rapid growth at crystal edges.[7] It displays the strongest diamagnetism among elements, repelling magnetic fields noticeably, and possesses the lowest thermal conductivity of any metal at approximately 7.97 W/(m·K).[6][4] The element adopts a rhombohedral crystal structure, characterized by three equal axes and angles of about 57.2°.[8] Bismuth has a density of 9.78 g/cm³ at 20 °C, a melting point of 271.3 °C, and a boiling point of 1564 °C.[9] Uniquely among metals, it expands upon solidification, increasing in volume by 3.32% relative to its solid form at the melting point, which causes it to float on its own liquid.[10] Its Mohs hardness measures 2.25, indicating relative softness comparable to arsenic or antimony.[4] The linear thermal expansion coefficient is 13.4 × 10^{-6} K^{-1}, and electrical resistivity stands at 1.29 μΩ·m at 20 °C, reflecting poor conductivity typical of post-transition metals.[11][4]| Property | Value |
|---|---|
| Density (20 °C) | 9.78 g/cm³ |
| Melting point | 271.3 °C |
| Boiling point | 1564 °C |
| Mohs hardness | 2.25 |
| Thermal conductivity | 7.97 W/(m·K) |
| Electrical resistivity (20 °C) | 1.29 μΩ·m |
| Linear thermal expansion coefficient | 13.4 × 10^{-6} K^{-1} |
| Volume expansion on solidification | 3.32% |