Metal hydrides are compounds formed when metals react with hydrogen. They typically consist of a metal atom bonded to one or more hydrogen atoms. These compounds can be classified into two main types: ionic metal hydrides, where hydrogen acts as a negative ion, and covalent metal hydrides, where hydrogen shares electrons with the metal. Metal hydrides are important in various applications, including energy storage and catalysis. For example, they can store hydrogen gas for fuel cells, making them valuable in the development of clean energy technologies. Additionally, they are used in chemical reactions to produce other compounds.