Hydrogen compounds

Source: Wikipedia, the free encyclopedia.

Hydrogen compounds are compounds containg the element

Brønsted–Lowry acids
are capable of donating H+ ions to bases.

Covalent and organic compounds

Water molecules have two hydrogen atoms and one oxygen atom.

While H2 is not very reactive under standard conditions, it does form compounds with most elements. Hydrogen can form compounds with elements that are more

electronegative, such as halogens (F, Cl, Br, I), or oxygen; in these compounds hydrogen takes on a partial positive charge.[1] When bonded to a more electronegative element, particularly fluorine, oxygen, or nitrogen, hydrogen can participate in a form of medium-strength noncovalent bonding with another electronegative element with a lone pair, a phenomenon called hydrogen bonding that is critical to the stability of many biological molecules.[2][3] Hydrogen also forms compounds with less electronegative elements, such as metals and metalloids, where it takes on a partial negative charge. These compounds are often known as hydrides.[4]

Water contains two hydrogen atoms covalently bonded to one oxygen atom,[5] and is one of the most well-studied compounds.[6]

Hydrogen is highly soluble in many

crystal lattice.[9] These properties may be useful when hydrogen is purified by passage through hot palladium disks, but the gas's high solubility is a metallurgical problem, contributing to the embrittlement of many metals,[10] complicating the design of pipelines and storage tanks.[11]

Hydrocarbons

Methane is a hydrocarbon.

Hydrogen forms a vast array of compounds with

heteroatoms that, because of their general association with living things, are called organic compounds.[12] The study of their properties is known as organic chemistry[13] and their study in the context of living organisms is known as biochemistry.[14] By some definitions, "organic" compounds are only required to contain carbon. However, most of them also contain hydrogen, and because it is the carbon-hydrogen bond that gives this class of compounds most of its particular chemical characteristics, carbon-hydrogen bonds are required in some definitions of the word "organic" in chemistry.[12] Millions of hydrocarbons
are known, and they are usually formed by complicated pathways that seldom involve elemental hydrogen.

Hydrides

Main article: Hydride
A sample of sodium hydride

Compounds of hydrogen are often called

electropositive element. The existence of the hydride anion, suggested by Gilbert N. Lewis in 1916 for group 1 and 2 salt-like hydrides, was demonstrated by Moers in 1920 by the electrolysis of molten lithium hydride (LiH), producing a stoichiometric quantity of hydrogen at the anode.[15] For hydrides other than group 1 and 2 metals, the term is quite misleading, considering the low electronegativity of hydrogen. An exception in group 2 hydrides is BeH2, which is polymeric. In lithium aluminium hydride
, the [AlH4]− anion carries hydridic centers firmly attached to the Al(III).

Although hydrides can be formed with almost all main-group elements, the number and combination of possible compounds varies widely; for example, more than 100 binary borane hydrides are known, but only one binary aluminium hydride.[16] Binary indium hydride has not yet been identified, although larger complexes exist.[17]

In

group 13 elements, especially in boranes (boron hydrides) and aluminium complexes, as well as in clustered carboranes.[18]

Protons and acids

Further information: Acid–base reaction

Oxidation of hydrogen removes its electron and gives H+, which contains no electrons and a nucleus which is usually composed of one proton. That is why H+ is often called a proton. This species is central to discussion of acids. Under the Brønsted–Lowry acid–base theory, acids are proton donors, while bases are proton acceptors.

A bare proton, H+, cannot exist in solution or in ionic crystals because of its unstoppable attraction to other atoms or molecules with electrons. Except at the high temperatures associated with plasmas, such protons cannot be removed from the

cationic
hydrogen attached to other species in this fashion, and as such is denoted "H+" without any implication that any single protons exist freely as a species.

To avoid the implication of the naked "solvated proton" in solution, acidic aqueous solutions are sometimes considered to contain a less unlikely fictitious species, termed the "hydronium ion" ([H3O]+). However, even in this case, such solvated hydrogen cations are more realistically conceived as being organized into clusters that form species closer to [H9O4]+.[19] Other oxonium ions are found when water is in acidic solution with other solvents.[20]

Although exotic on Earth, one of the most common ions in the universe is the H+3 ion, known as protonated molecular hydrogen or the trihydrogen cation.[21]

See also

References

Public Domain This article incorporates text from this source, which is in the public domain: http://wwwchem.uwimona.edu.jm/courses/CHEM1902/IC10K_MG_hydrogen.html

  1. ^ Clark, J. (2002). "The Acidity of the Hydrogen Halides". Chemguide. Archived from the original on 20 February 2008. Retrieved 9 March 2008.
  2. ^ Kimball, J. W. (7 August 2003). "Hydrogen". Kimball's Biology Pages. Archived from the original on 4 March 2008. Retrieved 4 March 2008.
  3. ^ IUPAC Compendium of Chemical Terminology, Electronic version, Hydrogen Bond Archived 19 March 2008 at the Wayback Machine
  4. ^ Sandrock, G. (2 May 2002). "Metal-Hydrogen Systems". Sandia National Laboratories. Archived from the original on 24 February 2008. Retrieved 23 March 2008.
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  11. ^ Christensen, C. H.; Nørskov, J. K.; Johannessen, T. (9 July 2005). "Making society independent of fossil fuels – Danish researchers reveal new technology". Technical University of Denmark. Archived from the original on 21 May 2015. Retrieved 19 May 2015.
  12. ^ a b "Structure and Nomenclature of Hydrocarbons". Purdue University. Archived from the original on 11 June 2012. Retrieved 23 March 2008.
  13. ^ "Organic Chemistry". Dictionary.com. Lexico Publishing Group. 2008. Archived from the original on 18 April 2008. Retrieved 23 March 2008.
  14. ^ "Biochemistry". Dictionary.com. Lexico Publishing Group. 2008. Archived from the original on 29 March 2008. Retrieved 23 March 2008.
  15. doi:10.1002/zaac.19201130116. Archived
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  19. doi:10.1021/j100372a014
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  21. doi:10.1021/ar00162a004
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