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My name is Selenium, but you can call me Se,
I take good care of myself, I'm disease free.
I’m a conductor at the presence of light,
And I can be gray and dull or red and bright.
I'm in the Oxygen Family but I'm the rarest of them all,If you need some of me just pick up the phone and call! |
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History
Jons Jakob Berzelius a Swedish man, found an unexpected presence of Tellurium in a sulfuric acid factory. He tried to figure out how this could possibly be in this particular factory but in no other. In 1817, a year later, he realized that although very similar, this element was not in fact tellurium, it was a new element that he had discovered. Just before announcing his discovery of this new element, that he named Selenium, after the Greek word selene, meaning moon, he identified a mineral that was rich in Selenium, he named it eucairite meaning “just in time.” Eucairite is made up of three elements, Copper, Silver, and Selenium (CuAgSe). |
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Overview
Selenium is a member of the Oxygen Family, but because of its close proximity to the Halogens, and its similarities, many people believe that it should be a member of the Halogens. The Oxygen Family is group 16 on the periodic table, and the other elements in the group are oxygen, sulfur, tellurium, and polonium.
Selenium and Tellurium are quite similar, they usually occur together, and have many similar uses. Recently Selenium has been put to use in some important places it is now used in photocopiers and laser printers. Also in photovoltaic cells that convert sunlight into electricity and in x-ray systems for medical purposes. |
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Uses
Gray Selenium is a photoconductor, meaning that although it is usually a poor conductor of electricity, it becomes a great conductor at the presence of light. When going from a dark room into a room with light, it increases by a factor of 1,000. For this reason, Selenium is valuable as a sensor of light, and is used in light switches, robotics, and light meters, but mainly in photocopy machines.
Selenium is also very bad for the human body, a few years after it was discovered it was considered to be toxic. But, recent studies have shown that Selenium, in small portions, may protect humans against cancer and heart disease. We do not know for sure, but experts say that Selenium is involved in the activity ofVitamin E.
Another use of Selenium is in Shampoos. Some compounds that contain Selenium have proved to control dandruff and have been used in many shampoos, but most well known to be in Head and Shoulders.
Selenium is also used as an additive to stainless steel to make it stronger, and in the glass industry it is used to take out the color of glass and replace it with a ruby red color. |
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Physical and Chemical Properties
There are two main allotropes of Selenium, one is an amorphous red glass-like powder, and the other has a bluish-gray, metallic appearance. The others are somewhere between. The amorphous forms of Selenium do mot have a specific boiling point or melting point, they just become softer, and sometimes change color or texture as they are heated. On the other hand, the metallic form of Selenium has a melting and boiling point (shown in the table.)
Selenium’s electrical properties are very important. Selenium is a semiconductor. IN the electronic industry, Selenium is used a lot, in things such as the manufacture of transistors for computers, cell phones, and hand-held electronic games. Selenium is also a photoconductor, it changed light energy to electrical energy, and it is easier to do so if there is an abundance of light.
Selenium is fairly reactive, and combines easily with Hydrogen Fuorine, chlorine, and bromine. It reacts with nitric and sulfuric acids, and reacts with many metals to make compounds called Selenides (MgSe). When reacting with Oxygen, it burns with a blue flame to form Selenium dioxide. |
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Occurance in Nature
Selenium is a very rare element, and is one of the 25 least common elements in Earth’s crust. Its abundance is .05-.09 parts per million. There is no ore where it can be mined with profit. Instead it is collected as a byproduct of mining other metals such as copper, iron, and lead. Selenium is mainly produced in Japan, Canada, Belgium, the United States, and Germany.
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Isotopes
There are six naturally occurring isotopes of Selenium, including Selenium-74, Selenium-76, Selenium-77, Selenium-78, Selenium-80, and Selenium-82. There are about twelve radioactive isotopes of Selenium. The radioactive isotope Selenium-75 is used commercially, to study the function of the pancreas and the parathyroid gland. It is injected into the bloodstream and immediately goes to one of the two organs or both. The isotope gives off radiation, and the technition can tell by the amount and the location of where the radiation is given off if the organ is healthy. |
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Health Effects
It is essential for both plants and animals to have a very small portion of Selenium, but large portions are quite dangerous. If animals don’t have Selenium in their diets, they develop weak muscles. In some parts of California, Selenium has been dissolved out of soil, and Lakes begin to have really high Selenium levels, birds and fish in those certain areas develop health problems.
In the late 1920’s scientists found that birds had been nesting in reservoirs and were developing deformities, and the problem was traced to high levels of Selenium. They had to build artificial lakes, and the birds were relocated to the artificial lakes. |
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Table |
Atomic Number |
34 |
Atomic Mass |
78.96 |
Phase at Room Temperature |
Solid |
Group Name |
Oxygen Family |
Melting Point |
493.65 Kelvin |
Group |
16 |
Period |
4 |
Classification |
Non-metal |
Boiling Point |
958 Kelvin |
Selenium is very similar to Tellurium, and they share many of the same properties, if you would like to learn more about Telurrium, click here. |
| Glossary |
| Allotropes |
A structurally differentiated form of an element |
| Amorphous |
lacking definite form; having no specific shape; formless |
| Semi-conductor |
a substance having electrical conductivity greater than insulators but less than good conductors. |
| Photo-conductor |
the increase in the electrical conductivity of a substance, often nonmetallic, caused by the absorption of electromagnetic radiation. |
| Isotopes |
different forms of the same element, with nuclei that have the same number of protons but different numbers of neutrons. |
| Radioactive-isotopes |
any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays. |
| Nitric Acids |
a colorless or yellowish, fuming, suffocating, caustic, corrosive, water-soluble liquid, HNO3, having powerful oxidizing properties, usually obtained from ammonia or from Chile saltpeter: used chiefly in the manufacture of explosives and fertilizers and in organic synthesis. |
| Sulfaric Acids |
a clear, colorless to brownish, dense, oily, corrosive, water-miscible liquid, H2SO4, usually produced from sulfur dioxide: used chiefly in the manufacture of fertilizers, chemicals, explosives, and dyestuffs and in petroleum refining. |
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