A chemical compound of hydrogen and another element or elements. Non-metallic hydrides (e.g. ammonia, methane, water) are covalently bonded. The alkali metals and alkaline earths (s-block elements) form salt-like hydrides containing the hydride ion H⁻, which produce hydrogen on reacting with water. Hydride-forming transition elements form interstitial hydrides, with the hydrogen atoms ‘trapped’ within the gaps in the lattice of metal atoms. Complex hydrides, such as lithium tetrahydroaluminate(III), have hydride ions as ligands; many are powerful reducing agents.