Selenium: Definition, Application, Properties and Health Effects

Selenium is a chemical element that belongs to the 16th group of the periodic table and the 4th period. Se is the symbol for the element selenium. It has the atomic number 34 and is a nonmetal element. It has properties that are similar to sulphur, tellurium, and arsenic. In the periodic table's 16th group, sulfur is put above selenium while tellurium is placed below selenium. In the 4th period and 15th group, arsenic is located to the left of selenium. It is a p – block element because it is present in the 16th group. It is sometimes classified as a metalloid due to its numerous characteristics.

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Selenium Atomic Number and Electronic Configuration 

Selenium has an atomic number of 34. It has the following electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴ or Ar 3d¹⁰ 4s² 4p⁴. It has 2 electrons in the K-shell, 8 electrons in the L-shell, 18 electrons in the M-shell, and 6 electrons in the N-shell, which is its outermost shell.

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What is Selenium?

Selenium is a nonmetallic chemical element that belongs to the periodic table's group XVI. It has chemical and physical properties that are similar to sulphur and tellurium. Selenium comes in a variety of allotropic forms, the most common of which are a red amorphous powder, a red crystalline substance, and metallic selenium, a grey crystalline metallike form. This last type is employed in photocells because it conducts electricity better in the light than in the dark. Selenium is unaffected by water and burns in the air, but it dissolves in concentrated nitric acid and alkalis.

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Applications of Selenium

Selenium is widely used in electronics, such as photocells, light meters, and solar cells, due to its photovoltaic and photoconductive qualities. The glass industry is the second greatest user of selenium: it is used to remove the color from glass and to give glasses and enamels a red color. The third min usage, which accounts for around 15% of the total, is sodium selenite, which is used in animal feeds and dietary supplements. Selenium is also used in photocopying and the toning of pictures. Its artistic application is to enhance and broaden the tonal range of black-and-white photographs. Other applications of selenium include plates of lead in storage batteries and rectifiers that convert AC to DC. In vulcanized rubbers, selenium is used to improve abrasion resistance. Anti-dandruff shampoos contain certain selenium compounds.

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• Selenium is used in Xerography to reproduce and copy documents, letters, and other types of documents.
• It's also utilized as a photographic toner and a stainless steel additive.
• Fluorescent quantum dots and surge protectors contain it. In many species, a little amount of selenium salts is required for normal cell activity.
• It's a component of baby formula.
• Many enzymes, including thioredoxin reductase and deiodinase, contain it.
• Manganese electrolysis uses selenium dioxide.
• It's utilized in the production of alloys.
• In brasses, for example, selenium replaces lead, which is more hazardous than selenium.
• It's also utilized in copper alloys.
• It's employed in copper indium gallium selenide thin-film solar cells.
• In industrial radiology, selenium-75 is employed as a gamma source.
• Blue LEDs contain zinc selenide.

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Selenium in the Environment

Selenium is one of the rarer elements on the planet's surface, even rarer than silver. Methyl derivatives of selenium can be found in the environment. Uncombined selenium is occasionally found, and there are roughly 40 known selenium-containing minerals, some of which can contain up to 30% selenium, but they are all rare, and they usually occur in conjunction with sulphides of metals like copper, zinc, and lead. It is released as a result of both natural and human activity. Because the element is naturally present in phosphate fertilizers and is frequently added as a trace nutrient, well-fertilized agricultural soil typically has about 400 mg/ton. Selenium cannot be generated or destroyed in its normal state as an element, however, it does have the power to alter forms.

Because selenium settles from the air and selenium from trash tends to end up in the soils of disposal sites, selenium levels in soils and rivers rise. 

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Physical and Chemical Properties of Selenium

• At 20 degrees Celsius, it is solid.
• Selenium has a relative atomic weight of 78.96.
• It has a melting point of 221 degrees Celsius.
• Selenium has a boiling point of 685°C.
• The hexagonal crystal structure is seen.
• It weighs 4.809 g cm^-3 and has a density of 4.809 g cm^-3.
• It produces a highly acidic oxide.
• Its electronegativity is 2.55 on the Pauling scale.
• It has a hexagonal crystal structure.
• It contains a large number of isotopes. It has five stable isotopes: 74Se, 76Se, 77Se, 78Se, and 80Se. Even though 80Se is its main isotope.
• It splits into many isotopes.

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Selenium Optical Properties

Selenium has a small amount of electrical conductivity. As a result, it's a semiconductor. Selenium is a photoconductor as well. It can convert light energy into electrical energy. It has been discovered in research that in the presence of light, its conductivity increases, implying that its photoconductivity increases as the intensity of light increases.

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Health Effects of Selenium

• Selenium can be ingested in a variety of ways by humans. Selenium is ingested by food or drink, or when we come into touch with soil or air containing high selenium concentrations. This isn't surprising, given selenium is abundant and widely distributed in nature.
• Because selenium is naturally contained in grains, cereals, and meat, selenium is mostly absorbed through food. To maintain optimum health, humans must absorb particular levels of selenium regularly. Selenium levels in food are normally sufficient to prevent disease caused by selenium deficiencies.
• Because numerous selenium-rich fertilizers were used on farmland in the past, selenium intake through food may be higher than usual in many circumstances.
• People who reside near hazardous waste sites will be exposed to more contaminants in the soil and air. Through irrigation, selenium from hazardous waste sites and farms will wind up in groundwater or surface water. As a result of this process, selenium ends up in local drinking water, temporarily increasing selenium exposure through the water.
• People who work in metal industries, selenium-recovery industries, and paint industries are more likely to be exposed to selenium, primarily through their breath. Coal and oil combustion release selenium into the atmosphere.
• People who consume a lot of grains grown near industrial locations may be exposed to more selenium through their meals. When selenium from hazardous waste disposals finds up in water wells, exposure to selenium through drinking water may be enhanced.
• In most cases, selenium is only exposed through the air in the workplace. It can make you feel dizzy, tired, and irritate your mucous membranes. When the level of exposure is extremely high, fluid might build in the lungs, causing bronchitis.
• Selenium absorption from the diet is normally sufficient to meet human requirements; shortages are uncommon. People may develop heart and muscular difficulties if there are shortages.
• When selenium intake is excessively high, negative health repercussions are likely to occur. The severity of these effects is determined by the amount of selenium in the diet and how often it is consumed.
• The health effects of different types of selenium range from brittle hair and malformed nails to rashes, fever, skin swelling, and severe aches. People who get selenium in their eyes report burning, irritation, and tearing.
• In extreme situations, selenium poisoning can be so severe that it can lead to death.
• Overexposure to selenium fumes can lead to pulmonary fluid accumulation, garlic breath, bronchitis, pneumonitis, bronchial asthma, nausea, chills, fever, headache, sore throat, shortness of breath, conjunctivitis, vomiting, stomach discomfort, diarrhea, and an enlarged liver. 

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Points To Remember

• There are six stable isotopes of selenium in nature. A total of fifteen additional isotopes have been identified. The element belongs to the sulphur family and, in its different forms and compounds, resembles sulphur.
• Selenium is found in some solids in sufficient concentrations to cause major side effects in animals that eat plants cultivated in such soils, such as locoweed.
• The melting and boiling point is 493.65 K and 958 K respectively.

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