Bismuth – facts and properties
- Symbol
- Bi
- Atomic number
- 83
- Atomic mass
- 208.98 u
- Period
- 6
- Group
- 15
- Category
- metal
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³
- Electronegativity
- 2.02
- Atomic radius
- 143 pm
- Valence electrons
- 5
- State at standard conditions
- solid
- Melting point
- 271.4 °C
- Boiling point
- 1564 °C
- Density
- 9.807 g/cm³
- Discovered
- 1753
Bismuth is a brittle, silvery heavy metal with a pink tinge and atomic number 83. Unlike most heavy metals it is hardly toxic. Laboratory-grown crystals gleam in rainbow colours, and many people know bismuth from stomach remedies. It counts as the heaviest practically stable element, because its only natural isotope decays so slowly that this was not measured until 2003. In solder and fishing weights bismuth takes the place of toxic lead.
Position in the periodic table
Occurrence and extraction
Bismuth is rarer in the Earth's crust than silver. It is occasionally found as the native metal, but mostly it sits in minerals such as bismuthinite, Bi₂S₃, or bismite, Bi₂O₃. Deposits of its own are rare, so the metal comes mostly as a by-product of smelting lead, copper, tin and tungsten ores. Worldwide less than twenty thousand tonnes a year are produced, against millions of tonnes of lead. China supplies most of it.
The metal was known in the Middle Ages but was long confused with lead, tin and antimony. Only in 1753 did the French chemist Claude François Geoffroy show that it is an element of its own. The origin of the name is uncertain. German miners called the metal Wismut, and chemistry uses the Latinised form.
Properties and reactions
Bismuth is the heaviest naturally occurring element of the nitrogen group. It lies in period 6 and group 15, below antimony, with lead on its left and polonium on its right. The atom has 5 valence electrons, its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³, and its electronegativity is 2.02. Bismuth melts as low as 271.4 °C, boils at 1564 °C and, at 9.807 g/cm³, is somewhat lighter than lead.
Bismuth shares one oddity with water: it expands as it solidifies, so a solid piece floats on the melt. When a melt cools slowly, stair-stepped crystals with a metallic shine grow. Their colours do not come from the metal itself but from a wafer-thin oxide layer. Light is reflected from the top and bottom of the layer, and depending on its thickness a different colour is strengthened.
Chemically bismuth is a nobler metal than lead. It is stable in dry air, and when heated it burns with a bluish flame to yellow bismuth oxide. The most common oxidation state is plus three. Compounds in the plus five state, such as sodium bismuthate, are powerful oxidising agents.
For a long time bismuth-209, the only natural isotope, counted as the heaviest stable atom. In 2003 a French research team used a bismuth germanate crystal to show that it is a very weak alpha emitter. Its half-life is about twenty billion billion years, more than a billion times the age of the universe. In practice bismuth is stable. The heaviest truly stable nucleus is the lighter lead-208.
For a heavy metal bismuth is unusually harmless, because many of its salts hardly dissolve.
Uses in everyday life and technology
Bismuth salts such as bismuth subsalicylate and bismuth citrate are found in remedies for stomach and bowel complaints. They coat the irritated lining. Combined with antibiotics, they also treat stomach ulcers caused by the bacterium Helicobacter pylori. A harmless side effect is black stools, caused by dark bismuth sulfide.
The second big field is replacing lead. Tin-bismuth solders melt at only about one hundred and forty degrees Celsius and spare delicate components. Fishing weights, shot for hunting near water and free-machining brass now contain bismuth instead of lead.
With lead, tin and cadmium, bismuth forms alloys that melt well below the boiling point of water, for example Wood's metal. Such alloys serve as fusible links: in a fire the metal gives way and sets off sprinkler systems.
Bismuth oxychloride gives eye shadow and lipstick a pearly lustre. Bismuth vanadate is a bright yellow pigment for paints and plastics and replaces cadmium colours. Bismuth germanate crystals in positron emission tomographs detect the radiation that doctors use to image the inside of the body.
Molecules containing this element
- Bismuth vanadate BiVO4
Quick question
What is the atomic number of bismuth (Bi)?
FAQ
Is bismuth radioactive?
Strictly speaking yes, because bismuth-209 decays by emitting alpha particles. Its half-life, however, is more than a billion times the age of the universe. The radiation is so weak that only special detectors can measure it, so in daily life bismuth counts as stable.
Why do bismuth crystals shimmer in rainbow colours?
A wafer-thin oxide layer forms on the metal. Light is reflected from its top and bottom, and the two beams overlap. Depending on the thickness of the layer a different colour is strengthened, so the crystals look multicoloured.
Is bismuth toxic?
No, at least not compared with lead, mercury or cadmium. Stomach remedies with bismuth salts have been in use for a long time. Only very high doses over a long period can lead to nerve damage, which is why dosage instructions matter.