Hidride

A hydride is a chemical species that contains hydrogen in combination with another element. In inorganic chemistry, hydrides are often described as compounds in which hydrogen exists as the hydride ion (H−) or as part of a lattice where hydrogen behaves as a reducing agent. In a broader sense, many covalent molecules containing hydrogen—such as water, ammonia, methane, and silanes—are also considered hydrides because they feature hydrogen bonded to another element, though not as H−.

Hydrides are commonly classified into several types. Ionic (or binary) hydrides form between hydrogen and electropositive metals, producing salts like sodium hydride (NaH) and calcium hydride (CaH2). These materials are typically strong reducing agents and can release hydrogen gas upon contact with water or acids. Interstitial metal hydrides arise when hydrogen atoms occupy interstitial sites in a metal lattice, as in palladium hydride (PdH_x), and are studied for hydrogen storage. Covalent hydrides include nonmetal hydrides such as methane (CH4), ammonia (NH3), water (H2O), and silane (SiH4). Complex hydrides, such as borohydride (BH4−) and aluminum hydride (AlH4−), are important in synthesis and materials chemistry and are used as reducing agents and in hydrogen storage chemistry.

Preparation methods vary with type: direct combination of hydrogen with elements under suitable conditions for ionic and covalent hydrides, or chemical synthesis using hydride donors for complex hydrides. Reactions of hydrides often involve transfer of hydride ions or release of hydrogen gas; many hydrides are strong reductants and must be handled with care, especially in the presence of moisture or oxidizing agents.

Applications span hydrogen storage, chemical reductions, and synthesis of materials and organometallic compounds. Safety considerations are important due to reactivity and potential flammability of many hydride species.