Selenium: Element 34 - Uses, Properties & Applications

Introduction

Selenium is a fascinating chemical element that occupies the 34th position on the periodic table. It is represented by the symbol Se and belongs to the chalcogen group, which also includes elements like oxygen, sulfur, and tellurium. In general, selenium is widely appreciated for its various applications in industries like electronics and medicine. It is a non-metal with a diverse range of allotropic forms, including red and black selenium.

Historical Background

Selenium was discovered in 1817 by the Swedish chemist Jöns Jacob Berzelius, who was studying an impurity isolated from sulfuric acid. Originally mistaking it for tellurium, Berzelius later recognized its distinct properties and named it Selenium after Selene, the Greek goddess of the moon, due to its resemblance to tellurium, which had been named for the Earth.

Physical Properties

Chemical Properties

Electron Configuration

Oxidation States

Common Compounds

Notable Chemical Reactions

Hydrogen selenide is an essential intermediate for synthesizing various organoselenium compounds and metallic selenides. However, caution is advised due to its toxic nature.

Selenium dioxide can further react with water to form selenious acid:

Zinc selenide is a valuable compound in the optoelectronics industry.

Selenium halides are essential for the preparation of other selenium compounds and are also used as reagents in organic synthesis.

In biological systems, selenium is a part of the active sites of several enzymes like glutathione peroxidases and thioredoxin reductases. These enzymes play critical roles in antioxidant defense mechanisms, making selenium vital for biological redox reactions.

Reactivity

Selenium is generally not very reactive at room temperature but becomes more reactive when heated or when in the presence of other reactive substances. It reacts with many metals to form selenides and also forms halides with halogens.

Abundance and Sources

Selenium is relatively rare and makes up approximately 0.05 ppm of the Earth’s crust. It is commonly found in sulfide ores of heavy metals like copper and lead. In nature, it occurs in minerals like eucairite and crooksite. Methods of extraction include refining of metal sulfides and recovery from the byproducts of copper refineries.

Uses and Applications

Selenium's unique properties make it indispensable in a myriad of applications. Its roles span multiple sectors, including industry, healthcare, and even everyday products. Let's delve deeper into these uses.

Industrial Uses

Medical Applications

Everyday Uses

Importance in Biological Systems

Safety

Interesting Facts

- Despite its toxicity, selenium is necessary for cellular function in many organisms, including humans, but only in trace amounts.

- Selenium was once used in early photovoltaic cells before the advent of more efficient materials.

- Selenium compounds can decolorize glass by neutralizing the green or yellow tints caused by iron impurities.

Conclusion

Selenium is an element of contrasts: vital in trace amounts but toxic in excess, valuable both to industrial applications and biological systems. It has a diverse array of uses, from electronics to medicine, and plays a crucial role in various biochemical processes. As we continue to study selenium, its full range of applications and properties is yet to be explored, making it an enduring subject of interest in the scientific community.