H2Se

Hydrogen selenide, with the chemical formula H2Se, is an inorganic compound that appears as a colorless gas at room temperature. It has a characteristic rotten-egg odor and is highly toxic and flammable. H2Se is the binary hydride of selenium and the conjugate acid of the selenide ion Se2−.

In terms of structure, H2Se is a bent molecule with two hydrogen atoms bound to a central selenium atom. The selenium atom bears lone pairs, giving a bond angle somewhat less than in water. In aqueous solution, H2Se behaves as a weak diprotic acid, with pKa1 around 4 and pKa2 around 11, forming HSe− and Se2− species at higher pH values.

Industrial or laboratory production methods include the direct reaction of hydrogen with elemental selenium at elevated temperature, or the acidification of selenide salts such as Na2Se to release H2Se gas. It can also be generated as a byproduct in processes involving selenium compounds. In air, H2Se is handled with caution as a hazardous gas.

H2Se readily participates in reactions typical of hydroselenides, including neutralization by acids to reform the gas and reactions with oxidants to form selenium-containing products. It serves as a precursor to organoselenium compounds and to various selenium-containing materials used in synthesis and materials science.

Safety is a critical consideration with hydrogen selenide. It is extremely toxic, with inhalation posing serious health risks and potential fatal outcomes. It is also flammable and can form explosive mixtures with air. Handling requires proper ventilation, gas detection, and appropriate protective equipment.