Hydrogen selenide (H2Se) is a chemical compound composed of hydrogen and selenium. It is a diatomic molecule, meaning it consists of two atoms (one hydrogen atom and one selenium atom) bonded together. Hydrogen selenide is a colorless gas with a pungent odor, similar to that of hydrogen sulfide (H2S). It is notable for its toxicity and its potential to react with various substances.

Here are some key points about hydrogen selenide:

1. Physical Properties: Hydrogen selenide is a gas at room temperature and atmospheric pressure. It has a similar molecular structure to hydrogen sulfide (H2S), and both molecules have a bent shape.
2. Odor: Like hydrogen sulfide, hydrogen selenide has a strong and unpleasant odor often described as resembling rotten eggs. Even at low concentrations, its odor can be easily detected.
3. Toxicity: Hydrogen selenide is highly toxic when inhaled or absorbed through the skin. It can affect the central nervous system and cause a range of health problems. Exposure to high concentrations can be lethal.
4. Natural Occurrence: Hydrogen selenide can be produced naturally through certain geological processes, leading to its presence in some natural gas deposits and volcanic gases.
5. Chemical Reactions: Hydrogen selenide is reactive and can participate in various chemical reactions. It can form salts with various metal cations.
6. Applications: Hydrogen selenide is not commonly used in practical applications due to its toxicity and reactivity. It is mainly studied for its chemical properties and behavior.
7. Safety Precautions: Due to its toxic and reactive nature, hydrogen selenide should be handled with extreme caution. Proper safety measures, protective equipment, and ventilation are essential when working with this compound.
8. Selenium Chemistry: Hydrogen selenide is part of the group of hydrogen chalcogenides, which also includes hydrogen sulfide (H2S), hydrogen telluride (H2Te), and hydrogen oxide (H2O).

Because of its toxicity and potential for adverse health effects, hydrogen selenide is not used extensively in industrial or commercial applications. It is primarily studied for its chemical properties and behavior in various scientific and research contexts.