Hydride
Definition and meaning of Hydride in chemistry.
A hydride is a chemical compound where hydrogen is bonded to a less electronegative element. The term also refers to the negatively charged hydride ion, written directly as H-. In these specific compounds, hydrogen carries a rare negative one oxidation state.
In more detail
Students often assume hydrogen always has a positive one charge in chemical compounds. This is true for common substances like water or acids, where hydrogen bonds to strongly electronegative elements. However, hydrogen can also bond to metals and other elements that pull weakly on their electrons.
In these specific cases, hydrogen actually holds the shared electrons more tightly. This gives the hydrogen atom a rare negative one oxidation state. Chemists divide hydrides into three main classes based on how they bond.
Ionic hydrides form when hydrogen reacts with highly reactive metals like sodium or calcium. These form crystalline salts containing distinct H- ions, and they are very strong reducing agents. They will react violently and catch fire if they touch liquid water.
Covalent hydrides form when hydrogen shares electrons with nonmetals or metalloids like boron or silicon. These specific bonds produce volatile gas molecules like silane (SiH4) or diborane (B2H6). Finally, metallic hydrides form when small hydrogen atoms physically squeeze into the empty gaps inside a solid transition metal. These metallic hydrides do not have strict chemical formulas, making them unique nonstoichiometric compounds.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Ion formula | H- (hydride ion) |
| Oxidation state of H | -1 |
| Main chemical types | Ionic, covalent, metallic (interstitial) |
| Key property (ionic) | Strong reducing agents that react violently with water |
Sodium hydride is a classic example of a highly reactive ionic hydride. Its chemical formula is NaH. When this solid white salt touches water, it reacts vigorously and dangerously. The negatively charged hydride ion pulls a proton directly off a water molecule. This violent chemical reaction creates sodium hydroxide (NaOH) and rapidly releases highly flammable hydrogen gas (H2). The exact reaction is NaH + H2O -> NaOH + H2.
Frequently asked questions
Why does hydrogen have a negative one oxidation state in hydrides?
Hydrogen is bonded to a metal or element that is less electronegative than itself. Hydrogen holds the electrons more tightly, giving it a negative charge instead of its usual positive charge.
Is normal water considered a hydride?
No. Oxygen is much more electronegative than hydrogen. In water, hydrogen loses electron density to oxygen and takes a positive one oxidation state, which excludes it from being a hydride.
How do metallic hydrides differ from ionic hydrides?
Ionic hydrides are salts with fixed chemical formulas and distinct ions. Metallic hydrides occur when hydrogen atoms squeeze into random gaps in a metal crystal, so they do not have fixed formulas.
Related terms
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