Description
تفصیل
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead. It is a brittle metal with a silvery white color when newly made, but often seen in air with a pink tinge owing to the surface oxide. Bismuth metal has been known from ancient times, although until the 18th century it was often confused with lead and tin, which each have some of the metal's bulk physical properties. The etymology is uncertain but possibly comes from Arabic "bi ismid" meaning having the properties of antimony or German words weisse masse or wismuth meaning white mass.
Bismuth is the most naturally diamagnetic of all metals, and only mercury has a lower thermal conductivity.
Bismuth has classically been considered to be the heaviest naturally occurring stable element. Recently, however, it has been found to be very slightly radioactive: its only naturally occurring isotope bismuth-209 decays via alpha decay into thallium-205 with a half-life of more than a billion times the estimated age of the universe.
Bismuth compounds (accounting for about half the production of bismuth) are used in cosmetics, pigments, and a few pharmaceuticals. Bismuth has unusually low toxicity for a heavy metal. As the toxicity of lead has become more apparent in recent years, alloy uses for bismuth metal (presently about a third of bismuth production), as a replacement for lead, have become an increasing part of bismuth's commercial importance.
Bismuth is a brittle metal with a white, silver-pink hue, often occurring in its native form with an iridescent oxide tarnish showing many colors from yellow to blue. The spiral stair stepped structure of a bismuth crystal is the result of a higher growth rate around the outside edges than on the inside edges.
Bismuth is stable to both dry and moist air at ordinary temperatures. When red-hot it reacts with water to make bismuth(III) oxide.
2 Bi + 3 H2O → Bi2O3 + 3 H2
It reacts with large amounts of fluorine to make bismuth(V) fluoride.
2 Bi + 5 F2 → 2 BiF5
It reacts with small amounts of fluorine to make bismuth(III) fluoride.
2 Bi + 3 F2 → 2 BiF3
It also reacts with the other halogens to make bismuth(III) halides.
2 Bi + 3 Cl2 → 2 BiCl3
2 Bi + 3 Br2 → 2 BiBr3
2 Bi + 3 I2 → 2 BiI3