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Hydrogen

For other uses, see Hydrogen (disambiguation).

Hydrogen, 00H
Hydrogen discharge tube.jpg
Purple glow in its plasma state
Hydrogen
Appearancecolorless gas
Standard atomic weight Ar°(H)
  • [1.00784, 1.00811]
  • 1.0080±0.0002 (abridged)[1]
Hydrogen in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
–
↑
H
↓
Li
– ← hydrogen → helium
Groupgroup 1: hydrogen and alkali metals
Periodperiod 1
Block  s-block
Electron configuration1s1
Electrons per shell1
Physical properties
Phase at STPgas
Melting point(H2) 13.99 K ​(−259.16 °C, ​−434.49 °F)
Boiling point(H2) 20.271 K ​(−252.879 °C, ​−423.182 °F)
Density (at STP)0.08988 g/L
when liquid (at m.p.)0.07 g/cm3 (solid: 0.0763 g/cm3)[2]
when liquid (at b.p.)0.07099 g/cm3
Triple point13.8033 K, ​7.041 kPa
Critical point32.938 K, 1.2858 MPa
Heat of fusion(H2) 0.117 kJ/mol
Heat of vaporization(H2) 0.904 kJ/mol
Molar heat capacity(H2) 28.836 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 15 20
Atomic properties
Oxidation states−1, +1 (an amphoteric oxide)
ElectronegativityPauling scale: 2.20
Ionization energies
  • 1st: 1312.0 kJ/mol
Covalent radius31±5 pm
Van der Waals radius120 pm
Color lines in a spectral range
Spectral lines of hydrogen
Other properties
Natural occurrenceprimordial
Crystal structure ​hexagonal
Hexagonal crystal structure for hydrogen
Speed of sound1310 m/s (gas, 27 °C)
Thermal conductivity0.1805 W/(m⋅K)
Magnetic orderingdiamagnetic[3]
Molar magnetic susceptibility−3.98×10−6 cm3/mol (298 K)[4]
CAS Number12385-13-6
1333-74-0 (H2)
History
DiscoveryHenry Cavendish[5][6] (1766)
Named byAntoine Lavoisier[7] (1783)
Isotopes of hydrogen
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
1H 99.9855%
Preview warning: Infobox H isotopes: Abundance percentage not recognised "na=99.9855%" cat#%
 stable
2H 0.0145%
Preview warning: Infobox H isotopes: Abundance percentage not recognised "na=0.0145%" cat#%
 stable
3H trace 12.32 y β− 3He
 Category: Hydrogen
| references

Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula H2. It is colorless, odorless, tasteless,[8] non-toxic, and highly combustible. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all normal matter.[9][note 1] Stars such as the Sun are mainly composed of hydrogen in the plasma state. Most of the hydrogen on Earth exists in molecular forms such as water and organic compounds. For the most common isotope of hydrogen (symbol 1H) each atom has one proton, one electron, and no neutrons.

In the early universe, the formation of protons, the nuclei of hydrogen, occurred during the first second after the Big Bang. The emergence of neutral hydrogen atoms throughout the universe occurred about 370,000 years later during the recombination epoch, when the plasma had cooled enough for electrons to remain bound to protons.[10]

Hydrogen is nonmetallic (except it becomes metallic at extremely high pressures) and readily forms a single covalent bond with most nonmetallic elements, forming compounds such as water and nearly all organic compounds. Hydrogen plays a particularly important role in acid–base reactions because these reactions usually involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a negative charge (i.e., anion) where it is known as a hydride, or as a positively charged (i.e., cation) species denoted by the symbol H+. The H+ cation is simply a proton (symbol p) but its behavior in aqueous solutions and in ionic compounds involves screening of its electric charge by nearby polar molecules or anions. Because hydrogen is the only neutral atom for which the Schrödinger equation can be solved analytically,[11] the study of its energetics and chemical bonding has played a key role in the development of quantum mechanics.

Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. In 1766–1781, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance,[12] and that it produces water when burned, the property for which it was later named: in Greek, hydrogen means "water-former".

Industrial production is mainly from steam reforming of natural gas, oil reforming, or coal gasification.[13] A small percentage is also produced using more energy-intensive methods such as the electrolysis of water.[13][14][15] Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing (e.g., hydrocracking) and ammonia production, mostly for the fertilizer market. It can be burned to produce heat or combined with oxygen in fuel cells to generate electricity directly, with water being the only emissions at the point of usage. Hydrogen atoms (but not gaseous molecules) are problematic in metallurgy because they can embrittle many metals.[16]

  1. ^ "Standard Atomic Weights: Hydrogen". CIAAW. 2009.
  2. ^ Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry. Academic Press. p. 240. ISBN 978-0123526519.
  3. ^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 978-0-8493-0486-6.
  4. ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 978-0-8493-0464-4.
  5. ^ "Hydrogen". Van Nostrand's Encyclopedia of Chemistry. Wylie-Interscience. 2005. pp. 797–799. ISBN 978-0-471-61525-5.
  6. ^ Emsley, John (2001). Nature's Building Blocks. Oxford: Oxford University Press. pp. 183–191. ISBN 978-0-19-850341-5.
  7. ^ Stwertka, Albert (1996). A Guide to the Elements. Oxford University Press. pp. 16–21. ISBN 978-0-19-508083-4.
  8. ^ "Hydrogen". Encyclopædia Britannica. Archived from the original on 24 December 2021. Retrieved 25 December 2021.
  9. ^ Boyd, Padi (19 July 2014). "What is the chemical composition of stars?". NASA. Archived from the original on 15 January 2015. Retrieved 5 February 2008.
  10. ^ Tanabashi et al. (2018) p. 358. Chpt. 21.4.1: "Big-Bang Cosmology" Archived 29 June 2021 at the Wayback Machine (Revised September 2017) by K.A. Olive and J.A. Peacock.[full citation needed]
  11. ^ Laursen, S.; Chang, J.; Medlin, W.; Gürmen, N.; Fogler, H. S. (27 July 2004). "An extremely brief introduction to computational quantum chemistry". Molecular Modeling in Chemical Engineering. University of Michigan. Archived from the original on 20 May 2015. Retrieved 4 May 2015.
  12. ^ Presenter: Professor Jim Al-Khalili (21 January 2010). "Discovering the Elements". Chemistry: A Volatile History. 25:40 minutes in. BBC. BBC Four. Archived from the original on 25 January 2010. Retrieved 9 February 2010.
  13. ^ a b Dincer, Ibrahim; Acar, Canan (14 September 2015). "Review and evaluation of hydrogen production methods for better sustainability". International Journal of Hydrogen Energy. 40 (34): 11094–11111. doi:10.1016/j.ijhydene.2014.12.035. ISSN 0360-3199. Archived from the original on 15 February 2022. Retrieved 4 February 2022.
  14. ^ "Hydrogen Basics – Production". Florida Solar Energy Center. 2007. Archived from the original on 18 February 2008. Retrieved 5 February 2008.
  15. ^ dos Santos, K. G.; Eckert, C. T.; De Rossi, E.; Bariccatti, R. A.; Frigo, E. P.; Lindino, C. A.; Alves, H. J. (2017). "Hydrogen production in the electrolysis of water in Brazil, a review". Renewable and Sustainable Energy Reviews. 68: 563–571. doi:10.1016/j.rser.2016.09.128.
  16. ^ Rogers, H. C. (1999). "Hydrogen Embrittlement of Metals". Science. 159 (3819): 1057–1064. Bibcode:1968Sci...159.1057R. doi:10.1126/science.159.3819.1057. PMID 17775040. S2CID 19429952.


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