Inorganic compound of hydrogen with another element .
Three common types are differentiated by their bonding . In saline (ionic) hydrides (see ionic bond ), the hydrogen is an anion , H - , and behaves like a halogen . Saline hydrides such as sodium hydride (NaH) and calcium hydride (CaH 2 ) react vigorously with water, giving off hydrogen gas (H 2 ), and are used as portable sources of it. Metallic hydrides, such as titanium hydride (TiH 2 ), are alloylike materials (see alloy ) with some properties of covalent bond ) are mostly compounds of hydrogen and nonmetallic elements; they include water , ammonia , hydrogen sulfide (H 2 S), and methane . In polymeric hydrides, the hydrogen forms bridges between other atoms (e.g., hydrides of boron and aluminum). Those hydrides give off large amounts of energy when burned and may be useful as rocket fuels.