What is hydride?



Answer:
Hydride is the name given to the negative ion of hydrogen, H−. It is also used as a more general term to describe compounds of hydrogen with other elements, particularly those of groups 1–16, whether or not they actually contain hydride ions. Protide, deuteride and tritide are used in the same way to describe ions or compounds which contain enriched hydrogen-1, deuterium or tritium respectively.

The variety of compounds formed by hydrogen is vast, arguably greater than that of any other element. Virtually every element of the periodic table (except the noble gases) forms one or more hydrides. These may be classified into three main types by the predominant nature of their bonding:

* Ionic hydrides, also known as saline hydrides;
* Covalent hydrides;
* Interstitial hydrides, which may be described as having metallic bonding.

Hydride ion

The hydride ion is the simplest possible anion, consisting of two electrons and a proton. Hydrogen has a relatively low electron affinity, 72.77 kJ/mol, and most of the chemistry of the hydride ion is dominated by the highly exothermic production of dihydrogen:

H− + H+ → H2; ΔH = −1675 kJ/mol

As a result, the hydride ion is one of the strongest bases known. It will extract protons from almost all other hydrogen-containing compounds, including liquid ammonia but with the exception of saturated hydrocarbons. The hydride ion is unknown in solution, as it would react with virtually any solvent, e.g.

NaH + H2O → H2 + NaOH; ΔH = −83.6 kJ/mol, ΔG = −109.0 kJ/mol

Alkanes, virtually the only solvents which are inert to hydride ions, are not sufficiently solvating to allow the dissolution of ionic hydrides.

The low electron affinity of hydrogen and the strength of the H–H bond (436 kJ/mol) means that the hydride ion is also a strong reducing agent:

H2 + 2e− ⇌ 2H−; Eo = −2.25 V

Only the alkali and alkaline earth metals can reduce molecular hydrogen to the hydride anion.

[edit] Precedence convention

According to IUPAC convention, by precedence (stylized electronegativity), hydrogen falls between group 15 and group 16 elements. Therefore we have NH3, 'nitrogen hydride' (ammonia), versus H2O, 'hydrogen oxide' (water).

[edit] Ionic hydrides

In ionic hydrides the hydrogen behaves as a halogen and obtains an electron from the metal to form a hydride ion (H−), thereby obtaining the stable electron configuration of helium or filling up the s-orbital. The other element is a metal more electropositive than hydrogen, usually one of the alkali metals or alkaline earth metals. The hydrides are called binary if they only involve two elements including hydrogen. Chemical formulae for binary ionic hydrides are either MH (as in LiH) or MH2 (as in MgH2). Gallium, indium, thallium and lanthanide hydrides are also ionic.

Their structures are purely crystalline.

They are prepared by reacting the element with hydrogen gas, under pressure if needed.

Ionic hydrides are usually used as reducing agents in synthetic chemistry, but they are too strongly basic and reactive to be used in pure form. Hydrides of lesser reactivity are more commonly used especially if the reaction can be carried out in water or organic solvents. Reduction by sodium borohydride (NaBH4) can be carried out in water. If a reactive hydride has to be used, the reduction will be carried out in a medium that readily dissolves the hydride ion without decomposition, for instance in liquid ammonia. Pure binary hydrides are still not often used even in those criteria. Lithium hydride is reduced in reactivity by forming lithium aluminium hydride (often abbreviated as LAH) with aluminium chloride.

4 LiH + AlCl3 → LiAlH4 + 3 LiCl

Water itself cannot serve as a medium for pure ionic hydrides or LAH because the hydride ion is a stronger base than hydroxide. Hydrogen gas is liberated if the hydride is immersed. The liberation is a typical acid-base reaction.

H− + H2O → H2 (gas) + OH−

Interstitial hydrides of the transitional metals

Their bonding nature vastly differs from element to element and changes according to external criteria such as temperature, pressure and electric current. Titanium and coinage metal hydrides are polymeric.

Other transitional metal hydrides are interstitial in nature. In these, molecules of hydrogen dissociate and hydrogen atoms settle in the octahedral or tetrahedral holes in the metal crystal lattice called the interstitial sites. Interstitial hydrides often have non-stoichiometric nature. Hydrogen atoms trapped in the lattice can migrate through it, reacting with impurities and worsening the properties of the material. In materials engineering this is known as hydrogen embrittlement.

For instance, Palladium hydride is not yet clearly considered a compound though it possibly forms Pd2H. The dihydrogen unit (H2) may also appear in the palladium lattice. Palladium adsorbs up to 900 times its own volume of hydrogen at room temperatures and was therefore once thought as a means to carry hydrogen for vehicle fuel cells. Hydrogen gas is liberated proportional to the applied temperature and pressure but not to the chemical composition.

Interstitial hydrides show certain promise as a way for safe hydrogen storage. During last 25 years many interstitial hydrides were developed that readily absorb and discharge hydrogen at room temperature and atmospheric pressure. They are usually based on intermetallic compounds and solid-solution alloys. However, their application is still limited, as they are capable of storing only about 2 weight percents of hydrogen, which is not enough for automotive applications.

[edit] Usage

Various metal hydrides are currently being studied for use as a means of hydrogen storage in fuel cell-powered electric cars and batteries. They also have important uses in organic chemistry as powerful reducing agents, and many promising uses in hydrogen economy.

Examples:

* nickel hydride - used in NiMH batteries
* palladium hydride - electrodes in cold fusion experiments
* lithium aluminium hydride - a powerful reducing agent used in organic chemistry
* sodium borohydride - selective specialty reducing agent, hydrogen storage in fuel cells
* sodium hydride - a powerful base used in organic chemistry
* diborane - reducing agent, rocket fuel, semiconductor dopant, catalyst, used in organic synthesis; also borane, pentaborane and decaborane
* arsine - used for doping semiconductors
* stibine - used in semiconductor industry
* phosphine - used for fumigation
* silane - many industrial uses, eg. manufacture of composite materials and water repellents
* ammonia - coolant, fertilizer, many other industrial uses
* hydrogen sulfide - component of natural gas, important source of sulfur
* chemically even water and hydrocarbons could be considered hydrides..
Hydride is the name given to the negative ion of hydrogen, H−. It is also used as a more general term to describe compounds of hydrogen with other elements, particularly those of groups 1–16, whether or not they actually contain hydride ions.
chemical formual is H-
and it is a bleach
when metals form their compounds with hydrogen they are known as hydrides
A hydride is a chemical compound of a hydrogen with other elements. Originally, the term hydride was reserved strictly for compounds containing hydride ions, usually in combination with metals, but the definition has been broadened to compounds (usually simple binary) involving hydrogen in direct bond with another element.
-any binary compound formed by the union of hydrogen and other elements

Hydride is the name given to the negative ion of hydrogen, H−. It is also used as a more general term to describe compounds of hydrogen with other elements, particularly those of groups 1–16, whether or not they actually contain hydride ions. Protide, deuteride and tritide are used in the same way to describe ions or compounds which contain enriched hydrogen-1, deuterium or tritium respectively.

The variety of compounds formed by hydrogen is vast, arguably greater than that of any other element. Virtually every element of the periodic table (except the noble gases) forms one or more hydrides. These may be classified into three main types by the predominant nature of their bonding:

Ionic hydrides, also known as saline hydrides;
Covalent hydrides;
Interstitial hydrides, which may be described as having metallic bonding.

list of main group hydride nomenclature:

alkali and alkaline earth metals: metal hydride
boron: borane and rest of the group as metal hydride
carbon: alkanes, alkenes, alkynes, and all hydrocarbons
silicon: silane
germanium: germane
tin: stannane
lead: plumbane
nitrogen: ammonia ('azane' when substituted), hydrazine
phosphorus: phosphine ('phosphane' when substituted)
arsenic: arsine ('arsane' when substituted)
antimony: stibine ('stibane' when substituted)
bismuth: bismuthine ('bismuthane' when substituted)
According to the convention above, the following are "hydrogen compounds" are not "hydrides":

oxygen: water ('oxidane' when substituted), hydrogen peroxide
sulfur: hydrogen sulfide ('sulfane' when substituted)
selenium: hydrogen selenide ('selane' when substituted)
tellurium: hydrogen telluride ('tellane' when substituted)
polonium: hydrogen polonide ('polonane' when substituted)
halogens: hydrogen halides

Various metal hydrides are currently being studied for use as a means of hydrogen storage in fuel cell-powered electric cars and batteries. They also have important uses in organic chemistry as powerful reducing agents, and many promising uses in hydrogen economy.

nickel hydride - used in NiMH batteries
palladium hydride - electrodes in cold fusion experiments
lithium aluminium hydride - a powerful reducing agent used in organic chemistry
sodium borohydride - selective specialty reducing agent, hydrogen storage in fuel cells
sodium hydride - a powerful base used in organic chemistry
diborane - reducing agent, rocket fuel, semiconductor dopant, catalyst, used in organic synthesis; also borane, pentaborane and decaborane
arsine - used for doping semiconductors
stibine - used in semiconductor industry
phosphine - used for fumigation
silane - many industrial uses, eg. manufacture of composite materials and water repellents
ammonia - coolant, fertilizer, many other industrial uses
hydrogen sulfide - component of natural gas, important source of sulfur
chemically even water and hydrocarbons could be considered hydrides .

...all the best.
dear. when an element combine with hydrogen. result is hydride...there are three type of hydrides ...1.acidic...like HCl. ...2.basic....like sodium hydride...3..neutral,. like.methane...thou can again classify..as...electron.rich.. METHANE.....,Dr Rakesh sharma.(sahil.study.circle)
It is simple that when any element combines with hydrogen then resulting compound is known as Hydrides.

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