Tin is a chemical element; it has the symbol Sn () and atomic number 50. A metallic-gray metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the so-called "tin cry", as a result of twinning in tin crystals.
Tin is a post-transition metal in group 14 of the periodic table of elements. It is obtained chiefly from the mineral cassiterite, which contains stannic oxide, . Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element on Earth, making up 0.00022% of its crust, and with 10 stable isotopes, it has the largest number of stable isotopes in the periodic table, due to its magic number of protons.
It has two main allotropes: at room temperature, the stable allotrope is β-tin, a silvery-white, malleable metal; at low temperatures it is less dense grey α-tin, which has the diamond cubic structure. Metallic tin does not easily oxidize in air or water.
The first tin alloy used on a large scale was bronze, made of tin and copper (12.5% and 87.5% respectively), from as early as 3000 BC. After 600 BC, pure metallic tin was produced. Pewter, which is an alloy of 85–90% tin with the remainder commonly consisting of copper, antimony, bismuth, and sometimes lead and silver, has been used for flatware since the Bronze Age. In modern times, tin is used in many alloys, most notably tin-lead soft solders, which are typically 60% or more tin, and in the manufacture of transparent, electrically conducting films of indium tin oxide in optoelectronic applications. Another large application is corrosion-resistant tin plating of steel. Because of the low toxicity of inorganic tin, tin-plated steel is widely used for food packaging as "tin cans". Some organotin compounds can be extremely toxic.
Characteristics Physical
Tin is a soft, malleable, ductile and highly crystalline silvery-white metal. When a bar of tin is bent, a crackling sound known as the "tin cry" can be heard from the twinning of the crystals. This trait is shared by indium, cadmium, zinc, and mercury in its solid state. Tin melts at about , the lowest in group 14, and boils at , the second lowest (ahead of lead) in its group. The melting point is further lowered to for 11 nm particles.
β-tin, also called white tin, is the allotrope (structural form) of elemental tin that is stable at and above room temperature. It is metallic and malleable, and has body-centered tetragonal crystal structure. α-tin, or gray tin, is the nonmetallic form. It is stable below and is brittle. α-tin has a diamond cubic crystal structure, as do diamond and silicon. α-tin does not have metallic properties because its atoms form a covalent structure in which electrons cannot move freely. α-tin is a dull-gray powdery material with no common uses other than specialized semiconductor applications. γ-tin and σ-tin exist at temperatures above and pressures above several GPa.
In cold conditions β-tin tends to transform spontaneously into α-tin, a phenomenon known as "tin pest" or "tin disease". Some unverifiable sources also say that, during Napoleon's Russian campaign of 1812, the temperatures became so cold that the tin buttons on the soldiers' uniforms disintegrated over time, contributing to the defeat of the Grande Armée, a persistent legend.
The α-β transformation temperature is , but impurities (e.g. Al, Zn, etc.) lower it well below . With the addition of antimony or bismuth the transformation might not occur at all, increasing durability. Commercial grades of tin (99.8% tin content) resist transformation because of the inhibiting effect of small amounts of bismuth, antimony, lead, and silver present as impurities.
Alloying elements such as copper, antimony, bismuth, cadmium, and silver increase the hardness of tin. Tin easily forms hard, brittle intermetallic phases that are typically undesirable. It does not mix into a solution with most metals and elements so tin does not have much solid solubility. Tin mixes well with bismuth, gallium, lead, thallium and zinc, forming simple eutectic systems.
Tin becomes a superconductor below 3.72 K and was one of the first superconductors to be studied. The Meissner effect, one of the characteristic features of superconductors, was first discovered in superconducting tin crystals.
Chemical Tin resists corrosion from water, but can be corroded by acids and alkalis. Tin can be highly polished and is used as a protective coat for other metals. When heated in air it oxidizes slowly to form a thin passivation layer of stannic oxide () that inhibits further oxidation.
Isotopes
Tin has seven to ten stable isotopes, the greatest number of any element. Their mass numbers are 112, 114, 115, 116, 117, 118, 119, 120, 122, and 124. Seven, Sn, are theoretically stable, while the remaining three, Sn, Sn, and Sn, are potentially radioactive to double beta decay, but have not been observed to decay. Tin-120 makes up almost a third of all tin. Tin-118 and tin-116 are also common. Tin-115 is the least common stable isotope. The isotopes with even mass numbers have no nuclear spin, while those with odd mass numbers have a nuclear spin of 1/2. It is thought that tin has such a great multitude of stable isotopes because of tin's atomic number being 50, which is a "magic number" in nuclear physics.
Tin is one of the easiest elements to detect and analyze by NMR spectroscopy, which relies on molecular weight and its chemical shifts are referenced against tetramethyltin ().
Of the stable isotopes, tin-115 has a high neutron capture cross section for thermal neutrons, at 30 barns. Tin-117 has a cross section of 2.3 barns, one order of magnitude smaller, while tin-119 has a slightly smaller cross section of 2.2 barns. Table of cross sections available at NIST: Neutron Scattering Lengths and cross sections. Before these cross sections were well known, it was proposed to use tin-lead solder as a coolant for fast reactors because of its low melting point. Current studies are for lead or lead-bismuth reactor coolants because both heavy metals are nearly transparent to fast neutrons, with very low capture cross sections. In order to use a tin or tin-lead coolant, the tin would first have to go through isotopic separation to remove the isotopes with odd mass number. Combined, these three isotopes make up about 17% of natural tin but represent nearly all of the capture cross section. Of the remaining seven isotopes tin-112 has a capture cross section of 1 barn. The other six isotopes forming 82.7% of natural tin have capture cross sections of 0.3 barns or less, making them effectively transparent to neutrons.
Tin has 33 unstable isotopes, ranging in mass number from 98 to 140. The unstable tin isotopes have half-lives of less than a year except for tin-126, which has a half-life of about 230,000 years. Tin-100 and tin-132 are two of the very few nuclides with a "doubly magic" nucleus; though they are unstable, being far off the valley of stability in neutron–proton ratio, the tin isotopes lighter than tin-100 and heavier than tin-132 are even less stable. Another 55 metastable isomers have been identified for tin isotopes between 111 and 131, the most stable being tin-121m, with a half-life of 43.9 years.
Etymology The word tin is shared among Germanic languages and can be traced back to reconstructed Proto-Germanic ; cognates include German , Swedish and Dutch . It is not found in other branches of Indo-European, except by borrowing from Germanic (e.g., Irish from English).
The Latin name for tin, stannum or stagnum, originally meant an alloy of silver and lead, and came to mean 'tin' in the fourth centuryEncyclopædia Britannica, 11th Edition, 1911, s.v. 'tin', citing H. Kopp—the earlier Latin word for it was , or "white lead". apparently came from an earlier (meaning the same substance), the origin of the Romance and Celtic terms for tin, such as French , Spanish , Italian , and Irish . The origin of / is unknown; it may be pre-Indo-European.American Heritage Dictionary
The suggests instead that came from Cornish , and is evidence that Cornwall in the first centuries AD was the main source of tin.
The ancient Greek word was κασσίτερος (kassíteros). Beekes suggests the name could be a demonym for the bronze age Kassite people (Neo-Assyrian 𒂵𒅆𒄿; ka₃-ši-i, kašši) of the Ancient Near East.
History
Tin extraction and use can be dated to the beginnings of the Bronze Age around 3000 BC, when it was observed that copper objects formed of polymetallic ores with different metal contents had different physical properties. The earliest bronze objects had a tin or arsenic content of less than 2% and are believed to be the result of unintentional alloying due to trace metal content in the copper ore. The addition of a second metal to copper increases its hardness, lowers the melting temperature, and improves the casting process by producing a more fluid melt that cools to a denser, less spongy metal. This was an important innovation that allowed for the much more complex shapes cast in closed molds of the Bronze Age. Arsenical bronze objects appear first in the Near East where arsenic is commonly found with copper ore, but the health risks were quickly realized and the quest for sources of the much less hazardous tin ores began early in the Bronze Age. This created the demand for rare tin metal and formed a trade network that linked the distant sources of tin to the markets of Bronze Age cultures.
Cassiterite (), the oxide form of tin, was most likely the original source of tin. Other tin ores are less common sulfides such as stannite that require a more involved smelting process. Cassiterite often accumulates in alluvial channels as placer deposits because it is harder, heavier, and more chemically resistant than the accompanying granite. Cassiterite is usually black or dark in color, and these deposits can be easily seen in river banks. Alluvial (placer) deposits may incidentally have been collected and separated by methods similar to gold panning.
Tin replaced silver as the main export commodity of Bolivia in the early 20th century as it was used in solder as the canning industry greatly expanded. Starting in the late 1920s tin prices began a long trend of gradual decline. During the Second World War Bolivian tin mining magnate Simón Iturri Patiño was believed to be one of the five wealthiest men in the world.
Later, in 1985 the crash of international tin prices led to the 1985 Bolivian economic crisis. Bolivian company Corporación Minera de Bolivia (COMIBOL) was forced to lay off over 20,000 miners.
Compounds and chemistry
In the great majority of its compounds, tin has the oxidation state II or IV. Compounds containing bivalent tin are called while those containing tetravalent tin are termed .
Inorganic compounds Halide compounds are known for both oxidation states. For Sn(IV), all four halides are well known: , , , and . The three heavier members are volatile molecular compounds, whereas the tetrafluoride is polymeric. All four halides are known for Sn(II) also: , , , and . All are polymeric solids. Of these eight compounds, only the iodides are colored.
Tin(II) chloride (also known as stannous chloride) is the most important commercial tin halide. Illustrating the routes to such compounds, chlorine reacts with tin metal to give whereas the reaction of hydrochloric acid and tin produces and hydrogen gas. Alternatively and Sn combine to stannous chloride by a process called comproportionation: