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Tin: structure, properties, obtaining, uses

It is a silvery, soft, ductile and malleable metal. It has an atomic number of 50, and its predominant oxidation states or numbers are +2 (Sn 2+ ) and +4 (Sn 4+ ), with tin (II) compounds, such as SnCl 2 , being good reducing agents.

Tin has the symbol Sn, which is an abbreviation of the Latin word “stannum.” Tin is a metal resistant to attack by water and air at room temperature; but in hot air it forms tin dioxide, SnO 2 .

The property of being resistant to corrosion, and having a low melting point, has served for tin to have numerous applications; such as metal surface coating and welding.

Another important property of tin is its ability to be part of alloys with various metals, the oldest being bronze, an alloy of copper and tin.

Discovery

Tin granules. Source: Nefronus, CC0, via Wikimedia Commons

Tin is a metal that has been known since ancient times. Therefore, it is not known who was its discoverer; much less, the year and place of its discovery.

Bronze is an alloy of copper with tin and arsenic. It is possible that the elaboration of this alloy is the consequence of a fortuitous and unintentional event, since the first bronze objects – in the Bronze Age – were made up of copper and only traces of arsenic.

These objects appeared in the Near East where arsenic is associated with copper. But from the beginning, the toxicity of arsenic was evidenced, achieving its replacement by tin in bronze, using cassiterite (SnO 2 ) mainly as a source of tin .

Tin chemical structure

As there are two allotropes: white tin or β-Sn, and gray tin or α-Sn, we will have two crystalline structures. That of β-Sn is body-centered tetragonal (bct), which characterizes the malleability of white tin.

Meanwhile, the structure of α-Sn is diamond-like; that is to say, the Sn atoms are linked forming networks of tetrahedra, without the proper existence of a metallic bond at all.

Tin also presents two other allotropes under different conditions of pressure (in the order of GPa) and temperature (above 161 ºC): σ-Sn and γ-Sn.

Electronic configuration

The abbreviated electron configuration of tin is as follows:

[Kr] 4d 10 5s 2 5p 2

Adding all the electrons we will have a total of 14, the same number that corresponds to its group. However, only the electrons of the 5s and 5p orbitals are those that participate in the chemical reactions of tin, since those of the 4d are not energetically available.

Tin Properties

Appearance and physical characteristics

Tin is a soft, ductile and malleable metal that can be cold rolled and spun. Its low melting point allows it to adhere to the clean surfaces of metals or alloys such as steel, copper and their alloys, thus protecting them from oxidation.

When a piece of tin is bent it creaks, emitting a characteristic sound known as the “tin cry”, a consequence of the crushing of the crystals.

Tin has two allotropic forms: β and α. The β form corresponds to a white solid and is responsible for the applications of tin; while the α form is a greyish powder.

Location of tin on the periodic table. Source: Image by Daniel Mayer or GreatPatton and released under terms of the GNU FDL

The β form occurs at temperatures above 13.2 ºC. When the temperature drops below 13.2 ° C, tin changes from the β form to the α form. This phenomenon is undesirable and is avoided by adding other metals to tin, such as antimony or bismuth, which block this change and prolong its useful life.

Tin is the first known superconductor at temperatures below 3.72 K.

Atomic number

fifty

Molar mass

118.71 g / mol

Melting point

231.93 ºC

Boiling point

2602 ºC

Density

Allotrope β: 7.265 g / cm 3

Allotrope α: 5.769 g / cm 3

Oxidation states

Tin has multiple oxidation states: -4, -3, -2, -1, 0, +1, +2, +3, +4. However, most of its compounds have tin with oxidation states +2 (Sn 2+ ) and +4 (Sn 4+ ).

Ionization energies

First: 708.6 KJ / mol

Second: 1411.8 kJ / mol

Third: 2943.0 kJ / mol

Electronegativity

1.96 on the Pauling scale

Reactivity

Tin is a metal resistant to the action of air and water at room temperature, but when heated in air it forms tin oxide (IV), SnO 2 , which is weakly acidic. It is attacked by acids and alkalis, and in the presence of oxygen it can act as a catalyst in some cases.

Obtaining

The mineral cassiterite is the main mineralogical source of tin. Source: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Tin, from the point of view of its occurrence, is a rare metal, since it has an abundance in the earth’s crust of just 2 ppm. The mineral cassiterite, a tin oxide mineral, is the only commercial source of tin.

Cassiterite is a blackish mineral found in muddy soils on the banks of rivers. Tin is extracted from cassiterite by heating it up to 1370ºC with coal or coke to produce its reduction.

The tin produced is impure, so it is treated with sodium hydroxide or hydrochloric acid to solubilize the tin. Then, this is subjected to electrolysis, being the anode of tin and the cathode of iron. Tin is deposited on the cathode, with a purity greater than 90%.

Uses / applications

Corrosion protection

Tin is a corrosion resistant metal. The so-called can or tinplate is a steel container, covered with a layer of tin to prevent oxidation.

Cans have been used to store food and other substances, for example: paints, lacquers, solvents, etc. But they are currently being replaced by aluminum or plastic containers. Tin-coated pipes and valves maintain the purity of water and beverages.

Alloys

The first uses for tin alloys were to make containers or utensils such as the cans and jars in this pantry. Source: Butterfly voyages – Serge Ouachée / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Man began to use bronze for more than 5000 years. Bronze is an alloy of copper and tin that is used in the making of tools, weapons, and household utensils.

In the same way, pewter, an alloy that was initially made of tin and lead, was used to make pots, dishes, etc. But due to the toxicity of lead, pewter is currently made from the alloy of tin, antimony, and cobalt.

The alloy of tin and lead has a low melting point, a property that has allowed its use in soldering, a technique that is used to join parts present in electrical and electronic circuits. There are auto parts in which tin is alloyed with iron, while alloys of aluminum, tin, and titanium are used in aerospace vehicles.

Zirconium alloys, also called Zircaloys, are used in nuclear reactors and have a small amount of tin.

Tin samples. Source: Ondřej Mangl, Public domain, via Wikimedia Commons

The alloy of silver and tin has been used in dental amalgams.

A crystalline alloy with the element niobium is a superconductor that operates at a temperature of 18 K and maintains its property in a strong magnetic field.

Glasses

Tin is used in the Pilkington process to produce window glass. The molten glass is placed on a molten tin surface, the glass acquiring a flat and smooth surface. This technique is still being used successfully.

Tin salts are sprayed onto glass to obtain an electrically conductive coating, which can be used to make frost-free windshield and lighting panels.

Tin compounds

Stannous chloride (SnCl 2 ) is used in tin plating and as a reducing agent in the manufacture of polymers and dyes. Stannous Fluoride (SnF 2 ) is an active ingredient in toothpastes.

Meanwhile, its oxide is a useful catalyst in certain industrial processes. In addition, it is used as a powder for polishing steel.

The organic compounds of tins are used as biocides and fungicides, being toxic to humans. Organic tin stabilizers are used to prevent changes in polyvinyl chloride from exposure to light and heat.

Stannic chloride (SnCl 4 ) is used as a perfume stabilizer and as a starting material for other tin salts.

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