Hydride is the isolated atomic hydrogen anion, H- or any compound containing
hydrogen and another element, more electropositive element or group. Hydride
consists of a singly charged positive nucleus and two electrons of which one
electron is weakly held and readily donative “extra”. There are some types of hydrides according to their bonding.
hydrides (saline hydrides): the hydrogen obtains an electron from a more
electropositive metal, usually one of the alkali metals, to be an anion, H- ,
and behaves like a halogen. Ionic hydrides react vigorously with water with
removing hydrogen gas (H2). Compounds that have hydrogen and one other element
only is called binary hydrides with general form of MH or MH2 such as sodium
hydride (NaH), lithium hydride (LiH), calcium hydride (CaH2), magnesium hydride
- Covalent hydrides: The hydrogen shares one or more pairs of
electrons with more electronegative elements (such as boron and aluminium) or
nonmetallic elements. Water, ammonia, hydrogen sulfide (H2S), hydrocarbons
(alkane, alkene and alkyne), and hydrazine belong to nonmetallic covalent
hydrides which behave as molecules and are normally gas or volatile liquids.
Hydrogen halides, boranes, silane, phosphines belong to covalent hydrides.
- Metallic hydrides: They are alloy-like materials which have individual
properties of metals. Their bondings are vary from element to element.
- Polymeric hydrides: the hydrogen has bridges forming three center bond with
other atoms such as boron, aluminum, and beryllium.
Hydrides which carry hydrogen can provide large amounts of heat when burned.
They can be used as a component in
jet fuels. They are less flammable and less volatile
than hydrocarbon fuels. They are relatively environmentally friendly because
they degrade quickly in the environment. Hydrides and
hydrido complexes containing this easily polarized ion are highly reactive,
strongly basic and powerfully reducing in synthetic reactions. They are
important reducing agents in industrial reactions though they are easily
destroyed in the relatively acidic compound water (H2O) and in air containing
dioxygen (O2). Examples of commercially useful hydride
- Sodium or
Potassium Hydride: strong base used in organic and inorganic fine chemical synthesis. It
is used as a condensation, alkylation and polymerization agent in making other
chemical compounds. It is used as a drying agent.
- Sodium or Potassium Borohydride: Used as a
selective reductant which can be used in aqueous solution. It converts aldehydes and
ketones to the corresponding alcohols in the manufacture of pharmaceuticals and
other fine chemicals. It is used as a hydrogen source and a foaming agent for
- Sodium Cyanoborohydride: Used as a
selective amination reductant. It converts aldehydes (chemoselective), ketones
(stereoselective) to the corresponding alcohols in the manufacture of
pharmaceuticals and other fine chemicals. It is used in the reductive alkylation
of amines, novel metals and oximes.
- Sodium Triacetoxyborohydride
- Lithium Aluminum Hydride: powerful reducing
agent used in organic
synthesis (for specific linkages in complex molecules).
- Sodium tri- or tert-butoxohydridoaluminate
- Sodium bis(2-methoxyethoxo) dihydridoaluminate
- Lithium Hydride:
flammable, white, translucent solids; decomposes at 850 C; reacts violently with
water to yield hydrogen and lithium hydroxide; used as a hydrogen source or
reducing agent to prepare other hydrides amides and 2H isotopic compound, as a
shielding material for thermal neutrons.
- Calcium Hydride: white crystals;
water; used in the production of chromium, titanium, and zirconium through the
- Titanium Hydride: black metallic powder whose dust is an
explosion hazard and which dissociates above 288 C; used in powder metallurgy,
hydrogen production, foamed metals, glass solder, and refractories, and as an
electronic gas getter.
- Zirconium Hydride: flammable, gray-black powder; used in powder metallurgy and nuclear moderators,
and as a reducing agent, vacuum-tube getter, and metal-foaming agent.