Tin

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Tin (stannum in Latin) is a chemical element with symbol Sn and atomic number 50. Main ore of tin is mineral cassiterite. Elemental tin occurs in nature too, but is very rare.

Properties

Chemical

Tin resists corrosion from water, but can be attacked by acids and alkalis. Tin can be highly polished and is used as a protective coat for other metals. In this case the formation of a protective oxide layer is used to prevent further oxidation.

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 "tin cry" can be heard due to the twinning of the crystals. Tin melts at 232 °C, property that allows him to be used in solders. Tin consists of two allotrope forms:

  • β-tin: also known as white tin, it's the standard metallic form, which is stable at and above room temperature. It is malleable and ductile. Its crystalline form is tetragonal.
  • α-tin: also known as gray tin, it's the nonmetallic form of tin which is stable below 13.2 °C. Gray tin is brittle and has a diamond cubic crystal structure, similar to diamond, silicon or germanium. α-tin has no metallic properties at all because its atoms form a covalent structure where electrons cannot move freely.

Commercial grades of tin (99.8%) resist transformation of β-tin into α-tin because of the inhibiting effect of the small amounts of other metals such as bismuth, antimony, lead or silver present.

Availability

Tin is available at electronic stores as solder, that contains >90% tin with traces of other metals, such as copper or bismuth. Older solders tend to contain lead. Bronze, which is an alloy of copper and tin is a poorer source, as only 12-30% is tin. Older dishes were made of pewter, that contains 85-99% tin.

Pure tin can be bought as ingots or bars from Rotometals, at around 19.66$ per pound.

Preparation

Tin can be prepared by reducing tin oxides (tin(II) oxide or tin(IV) oxide) with carbon at 1200°C. Since tin metal boils at 2600 °C, very little metal will be evaporated during the reduction.

2 SnO + C → 2 Sn + CO2
2 SnO2 + C → Sn + CO2

Projects

Handling

Safety

Tin has little toxicity, as most of its compounds. Organotin compounds however as know to be as toxic as cyanide.

Storage

Tin should be stored in closed bottles. If you want to avoid forming the α form, it should be kept at room temperature.

Disposal

Tin should be taken to metal recycling centers.

References

Relevant Sciencemadness threads