Selenium

toc Selenium By Liz and Nathan

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**//__Introduction__//**
Selenium is a non-metallic element. It is a member of the group XVI, and is a Chalcogen, in the Periodic Table of the Elements. It appears in many different forms, some of which include a red powder, a redish crystal, and a grey crystal. The grey crystal form is also known as Metallic Selenium (Introduction Link), and it possesses some interesting qualities. For example, it conducts electricity better in the light than in the dark. This abnormal feature has led to its use in photocells (see //__**Economics),**__// It burns in air, but it's not reactive with water, dissolving in nitric acid and alkalis. It has many applications in world industries, especially in electronics and commercial animal feeds.



//__**History**__//
Selenium was first discovered by Jons Jacob Berzelius, a Swedish Chemist, in 1817. At this time, Berzelius noticed an impurity contaminating the sulfuric acid being produced at a factory in Sweden. Berzelius first believed the impurity was tellurium, but then realized it was actually a previously unknown element. in 1957, it was discovered to be essential to all mammalian life. Through out the 1970s and 1980s it was often used in photocopiers and laser printers. ([|Selenium History]) At the current time, however, it is very important and widely used in glass manufacturing.The use of Selenium in electronics continues to decline.

__//**Economics**//__
Selenium has many applications in industry. For example, its electric conductivity means that it is ideal for use in many electronics, specifically photocells, which are used in electronics to help the electrical current flow more freely throughout the wires in electrical devices ([|Making Things]). Some common electronics that implement Selenium are light meters or solar cells. Selenium is also used commonly for staining or removing stain. In glassmaking, it is used to remove color from glass, however, it can also be used to tint glass or enamel a redish color. Because of the demand of its applications, Selenium can be obtained at a cost of roughly $300 per pound ([|Selenium]). In addition to electronics and glassmaking, Selenium is also a common ingredient in inks and copying toner. It is also an additive in stainless steel.

__//**Environment**//__
Selenium occurs naturally in the environment. It is often found in soils, as well as water, as a trace nutrient. Due to different irrigation techniques, more and more Selenium has ended up in our water (see **//__Health).__//** In 1930, Selenium was found to be a toxic agent responsible for livestock poisoning in the Western United States. The two diseases often associated with such conditions are "alkali disease" and "blind staggers". Since then, Selenium toxicity has been a major concern. Selenium weathered from rocks under oxidizing conditions (Selenates), is the most toxic form of Selenium. In some cases, however, Selenium is more helpful than hurtful. For example, certain plant species grow well in seleniferous soils. It has also been found that many plant species which have accumulated large amounts of Selenium have not faced any detrimental effects.

**//__Health__//**
Selenium is fundamentally important to human health. People come in contact with Selenium in food and water. There is often a fair amount in grain, cereals, and meat. Over the years, an increasing amount of Selenium has ended up in our drinking water. This increase, however, has not been seriously detrimental. In most cases, it helps humans meet the Selenium intake they should maintain to stay healthy. Selenium is an antioxidant, as well as a catalyst for the production of active thyroid hormone. Selenium is especially important to the immune system and is said to inhibit HIV progression to AIDS and reduce the risk of miscarriage. There is also a hypothesis that large intakes of Selenium will reduce cancer risk. ([|Se Health]) At the present moment, large clinical studies are being held to determine if this hypothesis is true or not. Due to the overwhelmingly positive health effects of Selenium, low and diminishing Selenium intake amounts have caused concern in some countries. If your body has a shortage of Selenium, you may suffer from heart and muscle problems. Although it is rare, if one consumes too much Selenium it may result in brittle hair, deformed nails, and possibly some type of rash.

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__//**Physics and Chemical Properties of Selenium (Se)**//__
Selenium has an atomic number of 34 and an atomic mass of 78.96 amu. Selenium is a non-metal element located in the Chalcogens section of the periodic table, or group 16. Chalcogen elements have metal like-properties. Selenium conducts electricity, which parallels its metalloid classification. Interestingly enough, the brighter the light, the better Selenium conducts electricity. When this element is found in the form of a crystal, the structure of the crystal is hexagonal, or six-sided. There are 9 isotopes of Selenium, they are: Se-73, Se-74, Se-75, Se-76, Se-77, Se-78, Se-79, Se-80, and Se-82. However, the atomic mass indicated that the most common isotope of Selenium is Se-79. The electronegativity of Selenium, according to Pauling, is 2.4, and the electronic configuration for Selenium is [ Ar ] 3d10 4s2 4p4 ([|Se Properties]).



__**//Fun Facts//**__
Selenium is derived from the Greek word //Selene//, meaning moon. It was found by Berzelius in association with Tellurium, the Greek word for //Earth.// Because they appeared to compliment each other, he thought a fitting name to be //Selene// or //Moon.// The two elements seem to accompany each other as the moon accompanies the earth.

__//**Works Cited**//__
"Chalcogens - Chemistry Encyclopedia - Structure, Elements, Metal, Gas, Number, Name, Salt."

Chemistry: Foundations and Applications. Web. 05 Jan. 2011. [].

"Chemical Elements.com - Selenium (Se)." Chemical Elements.com - An Interactive Periodic Table of the Elements. Web. 05 Jan. 2011. [].

Lancet. "The Importance of Selenium to Health." //PubMed.gov//. U.S. National Library of Medicine. Web. 05 Jan. 2011. .

"PHOTOCELL." Welcome — MakingThings. Web. 05 Jan. 2011. [].

"Selenium." Web. 05 Jan. 2011. [].

"Selenium (Se) - Chemical Properties, Health and Environmental Effects." Water Treatment and Purification - Lenntech. Web. 05 Jan. 2011. [].

"Selenium History." //Kendrick Wathershed Project//. Web. 05 Jan. 2011. .

"Selenium History." //THE MEDICAL NEWS | from News-Medical.Net - Latest Medical News and Research from Around the World//. Web. 06 Jan. 2011. .