Selenium Element Properties and Information
Selenium Element Properties and Information
Selenium is thirty-fourth element on the periodic table. Elements are arranged in the periodic table on the basis of the atomic number. Atomic number is the number of protons in the nucleus of the atom. Selenium has an atomic number of 34. It is located in the Group 16 and Period 4 of the periodic table of elements. It is denoted by Se. The name is derived from the Greek word ‘Selen’ which refers to Moon.
Jöns Jacob Berzelius observed red-white sediments which were collected at the bottom of the chamber in one of the works related to sulphuric acid. He analysed the sediments in 1817 and found that it contained a new metal which was undiscovered till then. It was selenium metal.
Selenium is quite rare. It is found in few rare minerals only. Since it is rare, it is obtained as a byproduct.
Physical Properties
- Selenium is a semi-metal which is found to exist in nature in two appearances; either silvery or red.
- The atomic mass of selenium is 78.96
- The melting point of selenium is 217°C
- The boiling point of selenium is 688°C
- The density of selenium is 4790 in S.I. units at 20°C
- Selenium has seven naturally occurring isotopes. Among them selenium-80 is the most abundant.
Chemical Properties
- Selenium forms two oxides; selenium oxide and selenium trioxide.
- Selenium trioxide is thermodynamically unstable and decomposes to dioxide at 185°C.
- Selenium monochloride and monobromide are well known. Iodides are not well known.
- Selenium forms selenium hexafluoride with fluorine. Selenium hexafluoride is relatively more reactive than sulfur hexafluoride. Also, it is toxic.
- Organoselenium compounds exists when selenium is able to form stable bonds with carbon. This is generally observed in the class of selenium (II) compounds.
Methods of Production
Extraction: Industrially selenium is always obtained as a byproduct. Generally, it is obtained as a byproduct in a copper processing plant. Residues obtained from the copper purification process are subjected to extraction using sodium carbonate to get selenium dioxide. The selenium dioxide is mixed with water and acidified to form selenous acid. Selenous acid is then bubbled with sulfur dioxide in order to get metallic selenium.
Relevance in Chemical and Related Industries
- Glass industries: About half of the total selenium metal produced is used to make glass. Iron impurities cause greenish-yellow tint to appear on glass. Selenium is used to cancel this colour by conferring red colour to the whole material.
- Fertilizer industries: Selenium is used in low doses to increase the resistance of crops and plants towards various environmental stress factors such as, draught, ultraviolet light, soil salinity, cold & hot temperatures, etc.
- Alloy: Lead is toxic in nature. There has been a need to reduce the content of lead in brass due to its toxicity. Selenium is used to do the job. When selenium is added to steel and cooper to improve machinability properties.
Relevance in Other Industries
- Radiography: Selenium-75 is used as a gamma source in industrial radiography.
- Electronics: Selenium has found its use in solar cells, photoconductors, rectifiers, etc.
Health Effects on Exposure
- Low Exposure: Exposure of selenium through air in selenium-centered workplaces tends to cause minor irritations of mucosa membrane, cause dizziness and fatigue.
- High Exposure: High intake of selenium can occur through food. Depending on the concentration of intake, it may cause; rashes, swelling, severe pains etc. If overexposure occured through air then it can cause asthma, bronchitis, pneumonitis, vomitting, fever, etc.
Effects on Surroundings
- Bio-magnification: When animals eat selenium rich plants, the over accumulation of the selenium tends to get passed along the food chain. Over concentration of selenium in animal body causes reproductive issues.
References:
https://en.m.wikipedia.org/wiki/Selenium
