Selenium 74, Packaging Type : Grey

Physical properties

Single-crystal selenium (99.9999%)

Solid selenium has several allotropic modifications:

Grey selenium (γ-Se, "metallic selenium") is the most stable modification with a hexagonal crystal lattice;

Red crystalline selenium - three monoclinic modifications: orange-red α-Se, dark red β-Se, red γ-Se;

Red amorphous selenium;

Black glassy selenium.

When gray selenium is heated, it produces a gray melt, and with further heating it evaporates with the formation of brown vapors. When the vapors are cooled sharply, selenium condenses as a red allotropic modification.

Chemical properties

Selenium is an analogue of sulfur and exhibits oxidation states of −2 (H2Se), +4 (SeO2) and +6 (H2SeO4). However, unlike sulfur, selenium compounds in the oxidation state +6 are very strong oxidizers, and selenium compounds (−2) are much stronger reducing agents than the corresponding sulfur compounds.

The simple substance selenium is much less chemically active than sulfur. Thus, unlike sulfur, selenium is not capable of burning in air on its own. Selenium can only be oxidized with additional heating, during which it slowly burns with a blue flame, turning into dioxide SeO2. Selenium reacts with alkali metals (very violently) only when melted

Unlike SO2, SeO2 is not a gas, but a crystalline substance that is highly soluble in water. Obtaining selenious acid (SeO2 + H2O → H2SeO3) is no more difficult than sulfurous acid. And by acting on it with a strong oxidizer (for example, HClO3), we obtain selenic acid H2SeO4, which is almost as strong as sulfuric acid.