Hydrogen




1 (none) ← hydrogen → helium
-
↑
H
↓
Li
General
number hydrogen, H, 1
nonmetals
block s
Appearancecolorless
(7) g·mol−1
Electron configuration 1s1
shell 1
Physical properties
PhasekJ·mol−1
Heat capacity(25 °C) (H2)
28.836 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K         15 20
Atomic properties
Electronegativity2.1 (Pauling scale)
Van der Waals radius120 pm
Miscellaneous
CAS registry number1333-74-0
Selected isotopes
Main article: Isotopes of hydrogen
iso NA half-life DM DE (MeV) DP
1H 99.985% H is neutrons
2H 0.015% H is neutrons
3H trace 12.32 y β− 0.019 3He
References
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Hydrogen (gas (H2).

Properties

With an atomic mass of 1.00794 amu, hydrogen is the lightest element.

Hydrogen is the most electrolysis, but this process is presently significantly more expensive commercially than hydrogen production from natural gas[2].

The most common naturally occurring acid-base chemistry, in which many reactions involve the exchange of protons between soluble molecules. As the only neutral atom for which the Schrödinger equation can be solved analytically, study of the energetics and bonding of the hydrogen atom has played a key role in the development of quantum mechanics.

Chemistry

The crystal lattice.[5]

Combustion

 

Hydrogen gas is highly flammable and will burn at concentrations as low as 4% H2 in air. The enthalpy of combustion for hydrogen is – 286 kJ/mol;[citation needed] it burns according to the following balanced equation.

2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ/mol

When mixed with oxygen across a wide range of proportions, hydrogen explodes upon ignition. Hydrogen burns violently in air. It ignites automatically at a temperature of 560 C [3] Pure hydrogen-oxygen flames burn in the ultraviolet color range and are nearly invisible to the naked eye, as illustrated by the faintness of flame from the main Space Shuttle engines (as opposed to the easily visible flames from the shuttle boosters). Thus it is difficult to visually detect if a hydrogen leak is burning. The Hindenburg zeppelin is an infamous case of hydrogen combustion (pictured), although the tragedy was due mainly to combustible materials in the skin of the zeppelin, which were also responsible for the coloring of the flames.[6] Another characteristic of hydrogen fires is that the flames tend to ascend rapidly with the gas in air, as illustrated by the Hindenberg flames, causing less damage than hydrocarbon fires. For example, two-thirds of the Hindenburg passengers survived the fire, and many of the deaths which occurred were from falling or from diesel fuel burns.[7]

Electron energy levels

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Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (December 2007)
Main article: Hydrogen atom

 

The ground state nm.

The energy levels of hydrogen can be calculated fairly accurately using the quantum electrodynamics).

In hydrogen liquid, the electronic ground state magnetic dipole transition. Radio telescopes can detect the radiation produced in this process, which is used to map the distribution of hydrogen in the galaxy.

H2 reacts directly with other oxidizing elements. A violent and spontaneous reaction can occur at room temperature with hydrogen fluoride.

Elemental molecular forms

 

There are two different types of diatomic hydrogen molecules that differ by the relative spin of their nuclei.[8] In the parahydrogen form the spins are antiparallel and form a singlet. At standard temperature and pressure, hydrogen gas contains about 25% of the para form and 75% of the ortho form, also known as the "normal form".[9] The equilibrium ratio of orthohydrogen to parahydrogen depends on temperature, but since the ortho form is an excited state and has a higher energy than the para form, it is unstable and cannot be purified. At very low temperatures, the equilibrium state is composed almost exclusively of the para form. The physical properties of pure parahydrogen differ slightly from those of the normal form.[10] The ortho/para distinction also occurs in other hydrogen-containing molecules or functional groups, such as water and methylene.

The uncatalyzed interconversion between para and ortho H2 increases with increasing temperature; thus rapidly condensed H2 contains large quantities of the high-energy ortho form that convert to the para form very slowly.[11] The ortho/para ratio in condensed H2 is an important consideration in the preparation and storage of liquid hydrogen: the conversion from ortho to para is iron compounds, are used during hydrogen cooling.[12]

A molecular form called cosmic rays. It has also been observed in the upper atmosphere of the planet Jupiter. This molecule is relatively stable in the environment of outer space due to the low temperature and density. H3+ is one of the most abundant ions in the Universe, and it plays a notable role in the chemistry of the interstellar medium.[13]

Compounds

Further information: Hydrogen compounds

Covalent and organic compounds

While H2 is not very reactive under standard conditions, it does form compounds with most elements. Millions of hydrides.

Hydrogen forms a vast array of compounds with urea). However, most of them also contain hydrogen, and since it is the carbon-hydrogen bond which 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. (This latter definition is not perfect, however, as in this definition urea would not be included as an organic compound).

In carboranes.[14]

Hydrides

Compounds of hydrogen are often called indium hydride has not yet been identified, although larger complexes exist.[17]

"Protons" and acids

Oxidation of H2 formally gives the oxonium ions are found when water is in solution with other solvents.[19]

Although exotic on earth, one of the most common ions in the universe is the H3+ ion, known as protonated molecular hydrogen or the triatomic hydrogen cation.[20]

Isotopes

Main article: Isotopes of hydrogen

 

Hydrogen has three naturally occurring isotopes, denoted 1H, ²H, and ³H. Other, highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but not observed in nature.[21][22]

  • 1H is the most common hydrogen isotope with an abundance of more than 99.98%. Because the proton, it is given the descriptive but rarely used formal name protium.
  • ²H, the other stable hydrogen isotope, is known as nuclear fusion.
  • ³H is known as radiolabel (this has become less common).

Hydrogen is the only element that has different names for its isotopes in common use today. (During the early study of radioactivity, various heavy radioactive isotopes were given names, but such names are no longer used). The symbols D and T (instead of ²H and ³H) are sometimes used for deuterium and tritium, but the corresponding symbol P is already in use for phosphorus and thus is not available for protium. IUPAC states that while this use is common it is not preferred.


Natural occurrence

 

Hydrogen is the most abundant element in the universe, making up 75% of nuclear fusion.

Throughout the universe, hydrogen is mostly found in the aurora. Hydrogen is found in the neutral atomic state in the Interstellar medium. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the Universe up to redshift z=4.[24]

Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2 (for data see table). However, hydrogen gas is very rare in the Earth's atmosphere (1 algae and is a natural component of flatus. Methane is a hydrogen source of increasing importance.


History

Discovery of H2

Hydrogen gas, H2, was first artificially produced and formally described by T. Von Hohenheim (also known as Antoine Lavoisier gave the element the name of hydrogen when he (with Laplace) reproduced Cavendish's finding that water is produced when hydrogen is burned. Lavoisier's name for the gas won out.

One of the first uses of H2 was for balloons, and later airships. The H2 was obtained by reacting helium (He).

Role in history of quantum theory

Because of its relatively simple atomic structure, consisting only of a proton and an electron, the hydrogen atom, together with the spectrum of light produced from it or absorbed by it, has been central to the development of the theory of chemical bond, which followed shortly after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.

One of the first quantum effects to be explicitly noticed (but not understood at the time) was a Maxwell observation involving hydrogen, half a century before full quantum mechanical theory arrived. Maxwell observed that the diatomic gas below room temperature and begins to increasingly resemble that of a monatomic gas at cryogenic temperatures. According to quantum theory, this behavior arises from the spacing of the (quantized) rotational energy levels, which are particularly wide-spaced in H2 because of its low mass. These widely spaced levels inhibit equal partition of heat energy into rotational motion in hydrogen at low temperatures. Diatomic gases composed of heavier atoms do not have such widely spaced levels and do not exhibit the same effect.[27]

Applications

Large quantities of H2 are needed in the petroleum and chemical industries. The largest application of H2 is for the processing ("upgrading") of fossil fuels, and in the production of reducing agent of metallic ores.

Apart from its use as a reactant, H2 has wide applications in physics and engineering. It is used as a lighter than air, having a little more than 1/15th of the density of air, it was once widely used as a lifting agent in balloons and airships. However, this use was curtailed after the Hindenburg disaster erroneously convinced the public that the gas was too dangerous for this purpose. Hydrogen is still regularly used for the inflation of weather balloons.

In more recent application Hydrogen is used pure or mixed with Nitrogen (sometime called Forming Gas) as a tracer gas for minute leak detection. Applications can be found in automotive, aircraft, consumer goods, medical device and chemical industry. Hydrogen is an authorized food additive (E 949) that allows food package leak testing among other anti-oxidizing properties.[29]

Hydrogen's rarer isotopes also each have specific applications. Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints.

The ITS-90 temperature scale at 13.8033 Kelvin.

Energy carrier

Main article: Hydrogen economy

Hydrogen is not an energy source, except in the hypothetical context of commercial tritium, a technology presently far from development. The sun's energy comes from nuclear fusion of hydrogen but this process is difficult to achieve on earth. Elemental hydrogen from solar, biological, or electrical sources costs more in energy to make than is obtained by burning it. Hydrogen may be obtained from fossil sources (such as methane) for less energy than required to make it, but these sources are unsustainable, and are also themselves direct energy sources (and are rightly regarded as the basic source of the energy in the hydrogen obtained from them).

Molecular hydrogen has been widely discussed in the context of energy, as a possible carrier of energy on an economy-wide scale. A theoretical advantage of using H2 as an energy carrier is the localization and concentration of environmentally unwelcome aspects of hydrogen manufacture from fossil fuel energy sources. For example, CO2 sequestration followed by carbon capture and storage could be conducted at the point of H2 production from methane. Hydrogen used in transportation would burn cleanly, without carbon emissions. However, the infrastructure costs associated with full conversion to a hydrogen economy would be substantial.[30] In addition, the energy density of both liquid hydrogen and hydrogen gas at any practicable pressure is significantly less than that of traditional fuel sources.

Production

H2 is produced in chemistry and biology laboratories, often as a by-product of other reactions; in industry for the reducing equivalents in biochemical reactions.

Laboratory syntheses

In the laboratory, H2 is usually prepared by the reaction of acids on metals such as zinc.

Zn + 2 H+ → Zn2+ + H2

Aluminum produces H2 upon treatment with acids but also with base:

2 Al + 6 H2O → 2 Al(OH)3 + 3 H2

The cathode. Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage. If, however, the gas is to be burnt on site, oxygen is desirable to assist the combustion, and so both electrodes would be made from inert metals. (Iron, for instance, would oxidize, and thus decrease the amount of oxygen given off.) The theoretical maximum efficiency (electricity used vs. energetic value of hydrogen produced) is between 80 – 94%. Bellona Report on Hydrogen

2H2O(aq) → 2H2(g) + O2(g)

In 2007, it was discovered that an alloy of aluminium and alumina, but the expensive gallium, which prevents to formation of an oxide skin on the pellets, can be re-used. This potentially has important implications for a hydrogen economy, since hydrogen can be produced on-site and does not need to be transported.

Industrial syntheses

Hydrogen can be prepared in several different ways but the economically most important processes involve removal of hydrogen from hydrocarbons. Commercial bulk hydrogen is usually produced by the carbon monoxide and H2.

CH4 + H2O → CO + 3 H2

This reaction is favored at low pressures but is nonetheless conducted at high pressures (20 atm; 600 inHg) since high pressure H2 is the most marketable product. The product mixture is known as "Hydrocarbons other than methane can be used to produce synthesis gas with varying product ratios. One of the many complications to this highly optimized technology is the formation of coke or carbon:

CH4 → C + 2 H2

Consequently, steam reforming typically employs an excess of H2O.

Additional hydrogen from steam reforming can be recovered from the carbon monoxide through the water gas shift reaction, especially with an CO2 + H2

Other important methods for H2 production include partial oxidation of hydrocarbons:

CH4 + 0.5 CO + 2 H2

and the coal reaction, which can serve as a prelude to the shift reaction above:[32] :CO + H2

Hydrogen is sometimes produced and consumed in the same industrial process, without being separated. In the ammonia (the world's fifth most produced industrial compound), hydrogen is generated from natural gas.

Hydrogen is also produced in usable quantities as a co-product of the major petrochemical processes of steam cracking and reforming. chlorine also produces hydrogen as a co-product.

Biological syntheses

H2 is a product of some types of fermentation to water.[33]

chloroplast.[34] Efforts have been undertaken to genetically modify cyanobacterial hydrogenases to efficiently synthesize H2 gas even in the presence of oxygen.[35]

Other rarer but mechanistically interesting routes to H2 production also exist in nature. phosphite to H2.


Etymology

Hydrogen, Latin: 'hydrogenium', is from Ancient Greek ὕδωρ (hydor): "water" and (genes): "forming". Ancient Greek γείνομαι (geinomai): "to beget or sire")[36]

The word "hydrogen" has several different meanings;

  1. the name of an element.
  2. an atom, sometimes called "H dot", that is abundant in space but essentially absent on Earth, because it dimerizes.
  3. a atomic hydrogen and hydrogen found in other compounds.
  4. the atomic constituent within all organic compounds, water, and many other chemical compounds.

The elemental forms of hydrogen should not be confused with hydrogen as it appears in chemical compounds.

See also

 v • d • e chemical elements

Hydrogen H2 | Nitrogen N2 | Oxygen O2 | Fluorine F2 | Chlorine Cl2 | Bromine Br2 | Iodine I2 | Astatine At2

References

  1. ^ Hydrogen in the Universe, NASA Website. URL accessed on 2 June 2006.
  2. ^ Hydrogen Basics - Production Florida Solar Energy Center.
  3. ^ Takeshita T, Wallace WE, Craig RS. (1974). Hydrogen solubility in 1:5 compounds between yttrium or thorium and nickel or cobalt. Inorg Chem 13(9):2282.
  4. ^ Kirchheim R, Mutschele T, Kieninger W. (1988). Hydrogen in amorphous and nanocrystalline metals Mater. Sci. Eng. 99: 457–462.
  5. ^ Kirchheim R. (1988). Hydrogen solubility and diffusivity in defective and amorphous metals. Prog. Mater. Sci. 32(4):262–325.
  6. ^ Dziadecki, John (2005). Hindenburg Hydrogen Fire. Retrieved on 2007-01-16.
  7. ^ The Hindenburg Disaster. Swiss Hydrogen Association. Retrieved on 2007-01-16.
  8. ^ Universal Industrial Gases, Inc. – Hydrogen (H2) Applications and Uses. Retrieved on September 15, 2005.
  9. ^ Tikhonov VI, Volkov AA. (2002). Separation of water into its ortho and para isomers. Science 296(5577):2363.
  10. ^ NASA Glenn Research Center Glenn Safety Manual. CH. 6 - Hydrogen. Document GRC-MQSA.001, March 2006. [1]
  11. ^ Milenko YY, Sibileva RM, Strzhemechny MA. (1997). Natural ortho-para conversion rate in liquid and gaseous hydrogen. J Low Temp Phys 107(1-2):77–92.
  12. ^ Svadlenak RE, Scott AB. (1957). The Conversion of Ortho-to Parahydrogen on Iron Oxide-Zinc Oxide Catalysts. J Am Chem Soc 79(20); 5385–5388.
  13. ^ H3+ Resource Center. Universities of Illinois and Chicago. Retrieved on 2007-02-09.
  14. ^ a b c Miessler GL, Tarr DA. (2004). Inorganic Chemistry 3rd ed. Pearson Prentice Hall: Upper Saddle River, NJ, USA
  15. ^ K. Moers, (1920). 2. Z. Anorg. Allgem. Chem., 113:191.
  16. ^ Downs AJ, Pulham CR. (1994). The hydrides of aluminium, gallium, indium, and thallium: a re-evaluation. Chem Soc Rev 23:175–83.
  17. ^ Hibbs DE, Jones C, Smithies NA. (1999). A remarkably stable indium trihydride complex: synthesis and characterization of [InH3{P(C6H11)3}]. Chem Commum 185–6.
  18. ^ Okumura M, Yeh LI, Myers JD, Lee YT. (1990). Infrared spectra of the solvated hydronium ion: vibrational predissociation spectroscopy of mass-selected H3O+•H2On•H2m.
  19. ^ Perdoncin G, Scorrano G. (1977). Protonation equilibria in water at several temperatures of alcohols, ethers, acetone, dimethyl sulfide, and dimethyl sulfoxide. 99(21); 6983–6986.
  20. ^ Carrington A, McNab IR. (1989). The infrared predissociation spectrum of triatomic hydrogen cation (H3+). Accounts of Chemical Research 22:218–22.
  21. ^ Gurov YB, Aleshkin DV, Berh MN, Lapushkin SV, Morokhov PV, Pechkurov VA, Poroshin NO, Sandukovsky VG, Tel'kushev MV, Chernyshev BA, Tschurenkova TD. (2004). Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei. Physics of Atomic Nuclei 68(3):491–497.
  22. ^ Korsheninnikov AA. et al. (2003). Experimental Evidence for the Existence of 7H and for a Specific Structure of 8He. Phys Rev Lett 90, 082501.
  23. ^ Jefferson Lab – Hydrogen. Retrieved on September 15, 2005.
  24. ^ Surveys for z > 3 Damped Lyα Absorption Systems: The Evolution of Neutral Gas. Retrieved on October 13, 2006.
  25. ^ "Basic Research Needs for the Hydrogen Economy." Argonne National Laboratory, U.S. Department of Energy, Office of Science Laboratory. 15 May 2003. [2]
  26. ^ Webelements – Hydrogen historical information. Retrieved on September 15, 2005.
  27. ^ Berman R, Cooke AH, Hill RW. Cryogenics, Ann. Rev. Phys. Chem. 7 (1956). 1–20.
  28. ^ Los Alamos National Laboratory – Hydrogen. Retrieved on September 15, 2005.
  29. ^ additives
  30. ^ See Romm, Joseph (2004). The Hype about Hydrogen, Fact and Fiction in the Race to Save the Climate. New York: Island Press. 
  31. ^ New process generates hydrogen from aluminum alloy to run engines, fuel cells.
  32. ^ a b c Oxtoby DW, Gillis HP, Nachtrieb NH. (2002). Principles of Modern Chemistry 5th ed. Thomson Brooks/Cole
  33. ^ Cammack, R.; Frey, M.; Robson, R. Hydrogen as a Fuel: Learning from Nature; Taylor & Francis: London, 2001
  34. ^ Kruse O, Rupprecht J, Bader KP, Thomas-Hall S, Schenk PM, Finazzi G, Hankamer B. (2005). Improved photobiological H2 production in engineered green algal cells. J Biol Chem 280(40):34170–7.
  35. ^ United States Department of Energy FY2005 Progress Report. IV.E.6 Hydrogen from Water in a Novel Recombinant Oxygen-Tolerant Cyanobacteria System. HO Smith, Xu Q. http://www.hydrogen.energy.gov/pdfs/progress05/iv_e_6_smith.pdf Accessed 16 August 2006.
  36. ^ LSJ, "of the father to beget, rarely of the mother to give birth.
  37. ^ Kubas, G. J., Metal Dihydrogen and σ-Bond Complexes, Kluwer Academic/Plenum Publishers: New York, 2001

Further reading

  • (1989). "Chart of the Nuclides". Fourteenth Edition. General Electric Company.
  • Ferreira-Aparicio, P; M. J. Benito, J. L. Sanz (2005). "New Trends in Reforming Technologies: from Hydrogen Industrial Plants to Multifuel Microreformers". Catalysis Reviews 47: 491–588.
  • Krebs, Robert E. (1998). The History and Use of Our Earth's Chemical Elements: A Reference Guide. Westport, Conn.: Greenwood Press. ISBN 0-313-30123-9. 
  • Newton, David E. (1994). The Chemical Elements. New York, NY: Franklin Watts. ISBN 0-531-12501-7. 
  • Rigden, John S. (2002). Hydrogen: The Essential Element. Cambridge, MA: Harvard University Press. ISBN 0-531-12501-7. 
  • Romm, Joseph, J. (2004). The Hype about Hydrogen, Fact and Fiction in the Race to Save the Climate. Island Press. ISBN 1-55963-703-X.  Author interview at Global Public Media.
  • Stwertka, Albert (2002). A Guide to the Elements. New York, NY: Oxford University Press. ISBN 0-19-515027-9. 
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