PTL:Tin
From ChemEd Collaborative
Tin is a metal in Group IVA and the 5th period. Other members of the group are carbon (C), silicon (Si), germanium (Ge), and lead (Pb). Tin makes up about .001% of the Earth's crust.
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Discovered
The metal has been known for centuries. Cassiterite (SnO2) is the only important tin-containing ore.
Name
Because of the long history of tin, it is not surprising that its name is an Anglo-Saxon word, but the symbol Sn comes from the Latin name for the metal, stannum.
β Tin Properties
Atomic Number: 50
Atomic Weight: 118.710
Melting Point: 505.08 K
Boiling Point: 2875 K
Superconduction Temperature: 3.72 K
Density of Solid: 7310 kg/m^3 (7.310 g/cm^3)
Electron Configuration: [Kr] 5s2 4d10 5p2
Atomic Radius: 140.5 pm
Atomic Volume: 16.3 cm^3/mol
Specific Heat: .227 J/g*K
Isotopes
[Mass Number] [Natural Abundance]
112 .97% 114 .66% 115 .34% 116 14.54% 117 7.68% 118 24.22% 119 8.59% 120 32.58% 122 4.63% 124 5.79%
These are the ten naturally occurring isotopes of tin. There are many other radioactive isotopes that have been synthesized in labs, but they are not stable like the naturally occurring isotopes.
Characteristics
Tin metal exists in two allotropic forms: β (white tin, body-centered tetragonal) and α (gray, diamond cubic). The ordinary form at room temperature is β tin, which is a silver-white malleable metal that is somewhat ductile. When β tin is bent or handled roughly, it literally "cries", making a high pitched sound, due to a change in the crystalline structure.
α tin vs β tin
Below 13.2°C, tin exists as α tin. This type of tin is not useful because it does not have metallic properties. Gray tin exists as a gray powder. β tin is the more useful variety of tin, and it is frequently used to coat other metals in order to protect against corrosion. The transformation from white tin to gray tin below 13.2°C can be prevented by mixing in small amounts of antimony or bismuth. This transformation is often referred to as the "tin pest" or "tin disease", and it is believed to have played a role in Napoleon's defeat in the Russian Campaign of 1812. The buttons on his soldiers' uniforms were made of tin, and the cold Russian winter might have caused them to disintegrate, which would have contributed to their defeat. However, the transformation generally takes a long time, so this story could merely be a legend. The "tin disease" caused the organ pipes in cold churches and cathedrals to crumble long ago.
Reactions
When heated in air, tin forms SnO2, and the metal is attacked by nitric acid at room temperature and hydrochloric acid when heated
Sn(s) + 2 HCl(aq) 
SnCl2(aq) + H2(g)
It also reacts with strong base when heated. It does not react with water, but does react with steam. The most important compound is tin(II) chloride (SnCl2·2H2O),
Sn(s) + Cl2(g) SnCl2(s)
which is widely used as a reducing agent.
Pure tin must be isolated from Cassiterite, the naturally occurring compound. Often times, this occurs through the reduction of Cassiterite by burning coal:
SnO2(s) + 2C (s) Sn(s) + 2CO(g)
Tin exists as Sn(II) or Sn(IV) in its compounds.
Uses
Uncovered artifacts suggest that people have been using tin for at least 5,500 years. Tin played a role in the development of civilization, as it is an important constituent of bronze, an alloy of Cu with 5-10% Sn. Bronze was used in Mesopotamia and in Egypt throughout recorded history. In South America, pure tin was found in Machu Picchu, the mountain home of the Incas, who apparently made bronze objects with varying compositions of Cu and Sn depending on the final use of the implement.
The metal was used by the Egyptians, the Phoenicians, the Greeks, and the Romans, and is mentioned in the Bible. Since the mineral cassiterite (SnO2) is the only important tin-containing ore, it must also have been known to the ancients. It was traded by the Phoenicians, and it has been said - although it is apparently a myth - that they found cassiterite in England and gave the name Cassiterides to those islands. Tin dishes have been used for hundreds of years, and tin plated iron was mentioned in 320 B.C. by Theophrastus. Cassiterite was mined in Cornwall, England for centuries, but tin ore now comes largely from Southeast Asia and Bolivia.
Due to its high cost and low strength, pure tin metal is rarely used. Rather it is used in various alloys and as a tin coating on steel. Indeed, tin plating accounts for 40% of the tin used. Tin is non-toxic and protects the underlying steel from corrosion. Thus, soft drinks and foods are packaged in such [cans]. At least 30,000 million such cans are sold each year in the U.S. alone! Tin salts can be sprayed onto glass, which produces electrically conductive coatings. These salts are often used for panel lighting and for frost-free windshields.
In the past, edible goods were often wrapped in sheets coated with tin, known as "tin foil." Now, aluminum is the metal of choice because it is more abundant and it is lighter. However, the product itself is still often referred to as tin foil.
The elemental form of tin is nontoxic to humans and most organisms. However, organic forms of tin are toxic if they manage to enter the body in some way.
Alloys
- The following are the main alloys of tin -
- Solder is typically about 33% Sn with the remainder largely lead.
- Bronze is usually 5-10% tin with the remainder largely Cu. If the tin content is adjusted correctly, bells cast from bronze have a marvelous tone. However, if too much tin is used, the bronze becomes brittle, which is how the Liberty Bell acquired its crack.
- Bearing metal, used in roller bearings, is an alloy of Sn, Pb, and Cu.
- Pewter, 90-95% Sn with some Sb and Cu, is used for tableware and decorative items.
- Type metal is composed of Pb, Sb, and Sn and is used to make printing type.
- Tin-niobium, is being tested for its exceptional superconducting capabilities.
Emission Spectra
This is the emission spectra for Tin.
