Tin

Tin is a chemical element that is classified as a Poor metal and also known by the chemical symbol "Sn" for Latin Stannum. Tin has ten stable isotopes, the most stable of any other element. Though tin is a metallic solid at room temperature, pure tin will transition into an unusable allotrope called grey tin if left under 13.2°C. Tin combines readily with other metals to form alloys such as bronze and Babbitt metal. Its most common form in nature is an oxide cassiterite (SnO2) and can be mined and processed to isolate the pure tin. This metal possesses a wide range of uses, from ceramic coloring agents to ceiling tiles. Its most common application, however, is as a thin non-corrosive coating in aluminum cans. Although the amount of tin ingested through tin cans is negligible, many organic compounds of tin are extremely toxic to humans.

Properties
Tin is a silvery-white and lustrous gray color located in the fifth row of the Periodic Table. Tin contains 50 protons and 50 electrons in its ground state, having several stable isotopes. In fact, tin has ten stable isotopes, the most of any other element. Tin is a solid at room temperature, with two varieties based on temperature. White tin (tin above 13.2°C) is metallic is chemically stable. Grey tin (tin below 13.2°C) develops a configuration of covalent bonds which detract all of its metallic properties and therefore has very few practical uses. However, mixing in small amount of bismuth or antimony can prevent the transition to grey tin. This element has a tetragonal structure that gives it relative strength and complicated crystalline structure. As tin is bent, a soft crackling noise, known as tin cry, is heard as a result of shearing multiple tin crystals within. When heated in the presence of oxygen, tin becomes SnO2, also known as cassiterite. Most natural tin is found in this form.

Tin is malleable, somewhat ductile, and semi-conductive. Similar to other metals, Tin has a relatively high melting point and boils at 2602°C. Tin naturally resists corrosion and is not easily oxidized due to its electron structure and four valence electrons and density of 7.287 g/ml. Because of these properties, tin was widely used as a protective coating on other metals, such as steel. Though isolated tin remains too soft to withstand heavy impact, tin combines readily with most metals to form alloys. For example, a mixture of tin and copper creates bronze, a highly durable alloy.

Occurrences
Although tin has the most number of stable isotopes of any other element, it is not very common in the earth's crust, comprising only about 1-2 parts per million (ppm). This makes tin roughly the 50th most common crustal element. Tin commonly occurs as the compound cassiterite (SnO2), also called tinstone. The metal can be isolated by smelting cassiterite with coke, fuel with few impurities and high carbon content. This cassiterite extraction method has been used for thousands of years to obtain pure tin. The major producers of tin are China, Peru, Bolivia, Indonesia, and Brazil, though the United States is its largest consumer. Other compounds of tin are manufactured artificially and do not occur naturally.

Uses
Tin is commonly used to coat other metals to form a non-corrosive surface due to its low oxidation rate. Steel cans are often coated with a thin layer of tin, hence the tin can. Tin alloys are used for several industrial and commercial purposes. Tin and fluoride (SnF2) as a compound may be used in toothpaste. Tin foil was widely used as food wrap, though aluminum foil has largely replaced it today. Tin and lead are used to produce pewter, Niobium-tin alloys are used as superconducting magnets, and tin oxide is used for gas sensors. As Tin oxide absorbs additional gas, it becomes more electrically conductive, a property that can be measured. When tin salts are coated on glass surfaces, the glass becomes electrically conductive, allowing for frost-free windshields and lighting.

Tin and chlorine (SnCl2) are used often to add weight to silk without compromising its sheen. Tin is also widely used in solder to fuse electrical connections or repair piping. This malleable metal is primarily used in the Pilkington glass-making process. Molten glass is poured onto a bed of molten tin, and their densities allow the glass to float on the surface. This leaves a perfectly smooth and parallel surface when the glass dries. Most window glass today is produced by this process. Historically, tin was used for roofing materials, flame-resistant coating on wooden doors, and ornaments around mirrors, ceilings, and windows. Tin-Chromium compounds (SnCrO2) are used to color china and porcelain. Babbitt metal is another alloy of tin, and may be mixed with arsenic, lead, or cadmium. Babbitt metal is used in the production of industrial ball bearings for large machinery. A thin layer of this soft alloy is coated on their surfaces and retains lubricant oils more effectively than simply iron or steel.

Health Effects
No known biological process naturally requires tin. Tin is not toxic to organisms in its pure form, but as tin binds with other elements, these compounds can be very damaging to life. Tin with carbon, organic tin, is not biodegradable and is difficult to break down in any digestive system. Additionally, organic tin absorbed in water can greatly harm fungi and phytoplankton, degrading the aquatic ecosystem. Specifically, these compounds are known to interfere with the reproductive, growth, and dietary functions of aquatic organisms. Exposure is greatest at shallow depths of water, where these compounds accumulate. Triethyltin, the most dangerous organic tin compound for humans, may cause several long term health issues including depression, liver damage, red blood cell shortage, or even brain damage. Short terms effects from minimal exposure to airborne tin compounds may include vomiting, nausea, diarrhea, and cramps. The US government standards of maximum levels of airborne tin compounds reaches 2 milligrams per cubic meter of air, and only 0.1 milligram per cubic meter for organic compounds. The amount of tin ingested from tin cans is negligible and of little to no risk to consumers.

Video
An explanation of tin (Left) and a time-lapse video of white tin transitioning into grey tin due to temperature (right). qEwCPJOP0Mg sXB83Heh3_c