This article is about the chemical element. For other uses, see Hydrogen (disambiguation).
Chemical element, symbol H and atomic number 1
Hydrogen, 1H
Purple glow in its plasma state
Hydrogen
Appearance
Colorless gas
Standard atomic weight Ar°(H)
[1.00784, 1.00811][1]
1.0080±0.0002 (abridged)[2]
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
(none) ← hydrogen → helium
Atomic number (Z)
1
Group
group 1: hydrogen and alkali metals
Period
period 1
Block
s-block
Electron configuration
1s1
Electrons per shell
1
Physical properties
Phase at STP
gas
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)[3]
when liquid (at b.p.)
0.07099 g/cm3
Triple point
13.8033 K, 7.041 kPa
Critical point
32.938 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, 0, +1 (an amphoteric oxide)
Electronegativity
Pauling scale: 2.20
Ionization energies
1st: 1312.0 kJ/mol
Covalent radius
31±5 pm
Van der Waals radius
120 pm
Spectral lines of hydrogen
Other properties
Natural occurrence
primordial
Crystal structure
hexagonal (hP4)
Lattice constants
a = 378.97 pm c = 618.31 pm (at triple point)[4]
Thermal conductivity
0.1805 W/(m⋅K)
Magnetic ordering
diamagnetic[5]
Molar magnetic susceptibility
−3.98×10−6 cm3/mol (298 K)[6]
Speed of sound
1310 m/s (gas, 27 °C)
CAS Number
12385-13-6 1333-74-0 (H2)
History
Discovery
Henry Cavendish[7][8] (1766)
Named by
Louis-Bernard Guyton de Morveau Antoine Lavoisier[9][10] (1787)
Isotopes of hydrogen
v
e
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
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Hydrogen is a chemical element; it has symbol H and atomic number 1. It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H2, sometimes called dihydrogen,[11] but more commonly called hydrogen gas, molecular hydrogen or simply hydrogen. It is colorless, odorless, tasteless,[12] non-toxic, and highly combustible. Constituting approximately 75% of all normal matter, hydrogen is the most abundant chemical substance in the universe.[13][note 1] Stars, including the Sun, primarily consist of hydrogen in a plasma state, while on Earth, hydrogen is found in water, organic compounds, and other molecular forms. The most common isotope of hydrogen (symbol 1H) consists of one proton, one electron, and no neutrons.
In the early universe, the formation of hydrogen's protons occurred during the first second following the Big Bang, with neutral hydrogen atoms only forming approximately 370,000 years later during the recombination epoch as the universe cooled and plasma had cooled enough for electrons to remain bound to protons.[14] Hydrogen, typically nonmetallic except under extreme pressures, readily forms covalent bonds with most nonmetals, contributing to the formation of compounds like water and various organic substances. Its role is crucial in acid-base reactions, which predominantly involve proton exchange among soluble molecules. In ionic compounds, hydrogen can take the form of either a negatively charged anion, where it is known as hydride, or as a positively charged cation denoted by the symbol H+. The cation, simply a proton (symbol p), exhibits specific behavior in aqueous solutions and in ionic compounds involves screening of its electric charge by surrounding polar molecules or anions. Hydrogen's unique position as the only neutral atom for which the Schrödinger equation can be directly solved has significantly contributed to the foundational principles of quantum mechanics through the exploration of its energetics and chemical bonding.[15]
Historically, hydrogen gas was first produced artificially in the early 16th century through the reaction of acids with metals. Henry Cavendish, between 1766 and 1781, identified hydrogen gas as a distinct substance[16] and discovered its property of producing water when burned—hence its name derived from the Greek "water-former".
Today, the majority of hydrogen production occurs through steam reforming of natural gas, with a smaller portion derived from energy-intensive methods such as the electrolysis of water.[17][18] Its primary industrial uses include fossil fuel processing, such as hydrocracking, and ammonia production, with emerging applications in fuel cells for electricity generation and as a heat source.[19] When used in fuel cells, hydrogen's only emission at the point of use is water vapor,[19] though combustion can produce nitrogen oxides.[19] Hydrogen's interaction with metals may cause embrittlement.[20]
^Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry. Academic Press. p. 240. ISBN 978-0123526519.
^Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
^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.
^Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 978-0-8493-0464-4.
^"Hydrogen". Van Nostrand's Encyclopedia of Chemistry. Wylie-Interscience. 2005. pp. 797–799. ISBN 978-0-471-61525-5.
^Emsley, John (2001). Nature's Building Blocks. Oxford: Oxford University Press. pp. 183–191. ISBN 978-0-19-850341-5.
^Miśkowiec, Paweł (April 2023). "Name game: The naming history of the chemical elements—part 1—from antiquity till the end of 18th century". Foundations of Chemistry. 25 (1): 29–51. doi:10.1007/s10698-022-09448-5.
^Stwertka, Albert (1996). A Guide to the Elements. Oxford University Press. pp. 16–21. ISBN 978-0-19-508083-4.
^"Dihydrogen". O=CHem Directory. University of Southern Maine. Archived from the original on 13 February 2009. Retrieved 6 April 2009.
^"Hydrogen". Encyclopædia Britannica. Archived from the original on 24 December 2021. Retrieved 25 December 2021.
^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.
^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]
^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.
^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.
^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.
^"Hydrogen Basics – Production". Florida Solar Energy Center. 2007. Archived from the original on 18 February 2008. Retrieved 5 February 2008.
^ abcLewis, Alastair C. (10 June 2021). "Optimising air quality co-benefits in a hydrogen economy: a case for hydrogen-specific standards for NO x emissions". Environmental Science: Atmospheres. 1 (5): 201–207. doi:10.1039/D1EA00037C. S2CID 236732702. This article incorporates text from this source, which is available under the CC BY 3.0 license.
^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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