Tin – facts and properties
- Symbol
- Sn
- Atomic number
- 50
- Atomic mass
- 118.71 u
- Period
- 5
- Group
- 14
- Category
- metal
- Electron configuration
- [Kr] 4d¹⁰ 5s² 5p²
- Electronegativity
- 1.96
- Atomic radius
- 145 pm
- Valence electrons
- 4
- State at standard conditions
- solid
- Melting point
- 231.93 °C
- Boiling point
- 2602 °C
- Density
- 7.287 g/cm³
- Discovered
- known since antiquity
Tin is a silvery-white, soft metal with atomic number 50. It has been known since antiquity and gave a whole era its name: in the Bronze Age, tin was alloyed with copper to make bronze. Today tin coats food cans, serves as solder in electronics and goes into many alloys. The metal creaks when bent, and in great cold it can crumble.
Position in the periodic table
Occurrence and extraction
Tin is not abundant in the Earth's crust, but it is important. The most important tin ore is cassiterite, or tinstone, an oxide with the formula SnO₂. It is found in veins in rock and in placer deposits, which are accumulations in river sands. Major producers are China, Indonesia, Myanmar and Peru; in Europe tin was once mined in the Ore Mountains and in Cornwall.
To extract tin, cassiterite is heated with coal. The carbon takes the oxygen from the tin oxide, and liquid tin is left. Because this works at moderate heat, people could obtain tin early on. In antiquity it was traded over long distances, and it has been known for thousands of years. There is therefore no year of discovery. The symbol Sn comes from the Latin stannum.
Properties and reactions
Tin is in period 5 and group 14, below germanium. Its electron configuration is [Kr] 4d¹⁰ 5s² 5p² and its electronegativity is 1.96. The metal has a density of 7.287 g/cm³, melts at 231.93 °C and boils at 2602 °C. The melting point is low for a metal, the boiling point high. The element has 4 valence electrons. With ten stable isotopes, tin has more than any other element. In compounds the oxidation numbers plus two and plus four are the most common.
Tin is fairly stable in air because a thin oxide layer forms. It is non-toxic and hardly reacts with water or weak acids. Strong acids and alkalis dissolve it, so it is an amphoteric metal.
When a bar of tin is bent, a creaking sound can be heard, the tin cry. It comes from crystals that slide against each other and form twins.
Tin occurs in several forms. At room temperature it is white, metallic beta tin. Below about 13 degrees Celsius alpha tin is the stable form, a grey form with a diamond structure that shows hardly any metallic properties. The change is very slow, however, and fastest in severe cold. Grey alpha tin is brittle and crumbles to powder. This tin pest has destroyed historical tin objects. It is an example of allotropy: the same atoms, arranged differently.
Uses in everyday life and technology
Bronze was the first important tin alloy. It consists of copper with an addition of roughly a tenth tin and is harder than pure copper. It gave the Bronze Age its name and is still used today for bells, bearings and sculptures. Tin is also a component of pewter tableware and organ pipes.
Tinplate is sheet steel with a thin layer of tin. Food cans are made from it. The tin layer protects the steel from rust and is non-toxic. Today the cans are usually also lacquered on the inside.
In electronics tin is the main component of solder, which joins components to circuit boards. Solder used to contain lead; today lead-free solders of tin with a little silver and copper are used. Other uses are the tin bath in the making of flat glass and tin oxide as a transparent, conductive coating.
Metallic tin is harmless, but certain organic tin compounds are toxic and were used, for example, in ship paints. That use is now banned.
Molecules containing this element
- Tin(II) chloride SnCl2
- Tin(II) fluoride SnF2
- Tin(IV) oxide SnO2
Quick question
What is the atomic number of tin (Sn)?
FAQ
What is bronze?
Bronze is an alloy of copper and tin, usually with roughly a tenth tin. It is harder than copper and casts well. The Bronze Age is named after this material.
What is tin pest?
In the cold, white metallic beta tin can change into grey alpha tin. Grey tin has a different crystal structure and crumbles to powder. The change is slow and happens mainly after long periods of severe cold.
Why does tin creak when it is bent?
The sound is called tin cry. When the metal is bent, regions in its crystals suddenly flip into a mirror-image orientation (twinning). In tin this is especially easy to hear.