hydridescompounds

Hydrides are chemical compounds in which hydrogen is bonded to another element and can be viewed as containing hydrogen in the hydride form (H−) or, in covalent hydrides, hydrogen atoms bonded to a more electronegative element. In inorganic chemistry the term hydride commonly refers to species where hydrogen behaves as a hydride ion; more broadly, it covers a range of compounds with hydrogen in varying oxidation states. Hydride compounds are often classified into ionic, covalent or molecular hydrides, interstitial (metallic) hydrides, and complex hydrides.

Ionic hydrides form mainly with alkali and alkaline earth metals. Examples include lithium hydride, NaH, KH, and CaH2. They are typically hard, high-melt solids with significant lattice energy. They react readily with water and alcohols to release hydrogen gas and form corresponding hydroxides, and they can act as hydride donors in organic synthesis or as precursors for hydrogen storage materials.

Covalent or molecular hydrides consist of hydrogen covalently bonded to nonmetals such as carbon, nitrogen, oxygen, sulfur, or halogens. Examples include water (H2O), ammonia (NH3), methane (CH4), hydrogen sulfide (H2S), and hydrogen fluoride (HF). These species are discrete molecules with varying polarity and acidity, and their hydridic character is weaker than in ionic hydrides.

Interstitial (metallic) hydrides form when hydrogen occupies interstitial sites in metal lattices, producing metal–hydrogen alloys such as palladium hydride (PdH_x). They often show reversible hydrogen absorption and desorption, relevant to storage and electrode materials. Complex hydrides contain coordinated anions such as BH4−, AlH4−, or NH2−; examples include NaBH4 and LiAlH4. These materials have high hydrogen content and can release H2 upon decomposition, with use as reducing agents and in hydrogen storage research.

Hydride chemistry has applications in energy storage, catalysis, and synthesis. Handling varies by class; many hydrides react with water or air and require appropriate precautions.