Hydride
Definition and meaning of Hydride in chemistry.
A hydride is a compound in which hydrogen is bonded to another element, or the hydride ion (H-) formed when a hydrogen atom gains one electron. In hydrides, hydrogen carries a -1 oxidation state, the opposite of the +1 it shows when bonded to more electronegative elements such as oxygen or chlorine.
In more detail
Hydrides fall into three main classes based on bonding. Ionic (saline) hydrides form between hydrogen and highly electropositive metals, like the alkali and alkaline earth metals, giving crystalline salts that contain discrete H- ions. Covalent (molecular) hydrides form between hydrogen and nonmetals or metalloids that are less electronegative than hydrogen, such as boron and silicon, through shared electron pairs, producing volatile molecules like diborane (B2H6) and silane (SiH4). Metallic (interstitial) hydrides arise when hydrogen atoms occupy gaps in a transition metal's crystal lattice, often giving nonstoichiometric formulas. Ionic hydrides are strong reducing agents and react violently with water.
Key facts
| Formula | H- (hydride ion) |
|---|---|
| Field | Inorganic Chemistry |
| Oxidation state of H | -1 |
| Main types | Ionic, covalent, metallic (interstitial) |
Sodium hydride reacts vigorously with water, releasing hydrogen gas: NaH + H2O -> NaOH + H2.
Frequently asked questions
Why does hydrogen have a -1 oxidation state in hydrides?
Because in these compounds hydrogen is bonded to an element less electronegative than itself, such as a metal, so it holds the shared or transferred electrons more strongly and is assigned a -1 oxidation state instead of its usual +1.
Is water a hydride?
No. Oxygen is more electronegative than hydrogen, so in water hydrogen has an oxidation state of +1, not -1, which excludes water from the hydride classification.