Selenium (Se)
| Atomic Number | 34 |
|---|---|
| Atomic Mass | 78.9718 u |
| Category | Polyatomic nonmetal |
| Electron Config | [Ar] 3d¹⁰ 4s² 4p⁴ |
| Appearance | black, red, and gray (not pictured) allotropes |
| Density (STP) | 4819 g/L |
| Melting Point | 494 K |
| Boiling Point | 958 K |
| Electronegativity | 2.55 (Pauling) |
| Ionization Energy | 941 kJ/mol |
| Atomic Radius | 115 pm |
| Crystal Structure | Simple Monoclinic |
| Discovered By | Jöns Jakob Berzelius (1817) |
Brief Introduction
Selenium (Se) is a nonmetal that exists in several allotropic forms, including a gray metallic form (most stable) and a red amorphous powder. It has semiconductor properties and is essential for life in trace amounts. Key details about Selenium (Se) are as follows:
Uses: Used in photovoltaic solar cells (CIGS and CdTe thin-film solar panels), photocopiers and laser printers (selenium drums), glass manufacturing (decolorization and red coloring), electronics and rectifiers, nutritional supplements (essential micronutrient), and in anti-dandruff shampoos (selenium sulfide).
Production/Extraction: Produced primarily as a byproduct of copper refining from anode slimes. Also recovered from lead and sulfuric acid production. Major producers include Japan, Germany, and Belgium (refining). Selenium is relatively rare.
History: Discovered by Jöns Jacob Berzelius in 1817 in Sweden while investigating a reddish sediment in sulfuric acid production. Named after Selene, the Greek goddess of the moon, as a companion element to tellurium (named after Earth).
Health Effects & Safety: Essential trace element for humans and animals (component of selenoproteins, antioxidant enzymes). Narrow margin between beneficial and toxic doses—deficiency causes Keshan disease (cardiomyopathy), while excess causes selenosis (hair loss, nail brittleness, neurological damage, garlic breath). Some forms are carcinogenic.
Price/Market: Moderate pricing; demand driven by electronics and solar cell applications. Supply tied to copper production. Growing interest in selenium for agricultural supplements and specialty applications.
Properties: Photoconductive (electrical conductivity increases with light exposure), semiconductor properties, exhibits -2, +4, and +6 oxidation states, gray metallic form is the most stable, distinctive garlic-like odor when heated, and high dielectric constant.
← Arsenic (As) · Bromine (Br) →