Tin

Tin is a soft, silvery metal in group 14 with the configuration [Kr] 4d10 5s2 5p2. It forms compounds in two oxidation states: +4, as in the ore cassiterite (SnO2), and +2, which becomes relatively more stable going down the group because the 5s electrons are held tightly and resist bonding (the inert-pair effect). Tin has two common allotropes. Metallic white tin is stable above 13.2 °C; below that, it can slowly crumble into brittle grey tin, a diamond-structured semiconductor. This transformation, called tin pest, is slow and needs long exposure to cold.

Tin has 50 protons, one of the nuclear 'magic numbers' that give extra stability, and it has ten stable isotopes, more than any other element. Alloyed with copper, it made bronze, the material that defined an age of human history. Today about half of all tin goes into solder, joining components on circuit boards; lead-free solders are mostly tin with small amounts of silver and copper. Tin plating protects steel food cans from corrosion, molten tin provides the perfectly flat bed on which window glass is made, and organotin compounds stabilize PVC plastics.

Discovery

Tin has been used for over 5,000 years. By about 3000 BCE, metalworkers in the Near East were alloying it with copper to make bronze, which is harder and casts better than copper alone. Tin ore was scarce, so long trade routes brought it from Cornwall, Iberia and Central Asia. The English word 'tin' is Germanic in origin, and the symbol Sn comes from the Latin stannum.