What Is Hydrogen Selenide?
Hydrogen selenide is a compound of selenium and hydrogen.
Its chemical formula is represented by H2Se. It is normally found as a colorless gas with a garlic-like odor and toxic properties similar to hydrogen sulfide. In aqueous solution (hydro selenide acid), it easily ionizes into selenide ion (Se2-) and hydrogen ion. Therefore, it is acidic.
Uses of Hydrogen Selenide
Hydrogen selenide is obtained by reacting selenium with aluminum powder using a magnesium ribbon fire to form aluminum selenide, followed by a drop of water in a nitrogen stream.
It is mainly used in the synthesis of organoselenium compounds. Organoselenium compounds include selenol, selenide, and diselenide, which are also used as synthetic raw materials for other compounds. They are also used to add small amounts of selenium to semiconductors (doping).
Properties of Hydrogen Selenide
Hydrogen selenide is similar to hydrogen sulfide in the following ways. This is probably due to the fact that selenium and sulfur are members of the same group 16 element (chalcogen). Hydrogen selenide and hydrogen sulfide both have similar properties as hydrogen compounds of chalcogen.
1. Low Boiling Point
Hydrogen selenide has a boiling point of -41.25°C. The boiling point of hydrogen sulfide is -60°C, which is close, but the boiling point of water (H2O), a hydrogen compound of the same chalcogen as selenium and sulfur, is 100°C, which is very high.
Because liquid water is strongly bonded to water molecules by hydrogen bonds, high energy is required to break these bonds and vaporize it. Water molecules are polar molecules, which means that there is an electrical bias within the molecule. Thus, slightly positively charged hydrogen in one water molecule is electrically attracted to slightly negatively charged oxygen in a nearby water molecule.
Hydrogen selenide and hydrogen sulfide are also polar molecules, but their polarity is smaller because the electronegativity of selenium and sulfur is only slightly greater than that of hydrogen. Therefore, hydrogen bonds are weak and the boiling point is low as a result.
2. Pungent Odor
Hydrogen selenide has a strong garlic-like odor, which irritates the mucous membranes of the nose and respiratory tract when inhaled. Hydrogen sulfide also has a pungent odor that is described as “rotten egg smell.”
3. When Dissolved in Water, It Exhibits Acidity.
When hydrogen selenide is dissolved in water, it ionizes into selenide ion (Se2-) and hydrogen ion. It is, therefore, acidic. Hydrogen sulfide, when dissolved in water, also ionizes into hydrogen sulfide ion (HS-) and sulfide ion (S2-) and hydrogen ion, resulting in acidity.
4. Easily Flammable
Hydrogen selenide is highly flammable and forms water and selenium dioxide when it burns. Hydrogen sulfide burns to form water and sulfur dioxide. Selenium dioxide is solid at room temperature, while sulfur dioxide is a gas at room temperature.
Structure of Hydrogen Selenide
Hydrogen selenide has a folded molecular structure with a bond angle of about 91° between the two hydrogen atoms. Because of this structure, it is slightly polar.
Other Information About Hydrogen Selenide
1. Production of Hydrogen Selenide
When water is added to aluminum selenide, it is formed together with aluminum oxide. When hydrochloric acid is added to aluminum selenide, it is formed together with aluminum chloride.
In addition to the method of producing hydrogen selenide from selenium and metal compounds, hydrogen selenide can also be produced by the direct reaction of selenium alone with hydrogen.
2. Safety Information on Hydrogen Selenide
Hydrogen selenide is designated as a hazardous substance and flammable gas.
Hydrogen selenide is designated as a special high-pressure gas. Other designated special high-pressure gases include arsine, disilane, diborane, phosphine, monogermanes, and monosilane, all of which are flammable, toxic, and dangerous gases.
Contact with water, alkalis, oxidizers, or halogenated hydrocarbons can cause fire or explosion. When in contact with air, there is a risk of forming explosive gas mixtures.