1 (none) ← hydrogen → helium - ↑ H ↓ Li Periodic table - Extended periodic table
General
Name, symbol, number	hydrogen, H, 1
Chemical series	nonmetals
Group, period, block	1, 1, s
Appearance	colorless
Standard atomic weight	1.00794(7) g·mol−1
Electron configuration	1s1
Electrons per shell	1
Physical properties
Phase	gas
Density	(0 °C, 101.325 kPa) 0.08988 g/L
Melting point	14.01 K (−259.14 °C, −434.45 °F)
Boiling point	20.28 K (−252.87 °C, −423.17 °F)
Triple point	13.8033 K (-259°C), 7.042 kPa
Critical point	32.97 K, 1.293 MPa
Heat of fusion	(H2) 0.117 kJ·mol−1
Heat of vaporization	(H2) 0.904 kJ·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
Crystal structure	hexagonal
Oxidation states	1, −1 (amphoteric oxide)
Electronegativity	2.20 (Pauling scale)
Ionization energies	1st: 1312.0 kJ·mol−1
Atomic radius	25 pm
Atomic radius (calc.)	53 pm
Covalent radius	37 pm
Van der Waals radius	120 pm
Miscellaneous
Thermal conductivity	(300 K) 180.5 m W·m−1·K−1
Speed of sound	(gas, 27 °C) 1310 m/s
CAS registry number	1333-74-0
Selected isotopes
Main article: Isotopes of hydrogen iso NA half-life DM DE (MeV) DP 1H 99.985% 1H is stable with 0 neutrons 2H 0.015% 2H is stable with 1 neutrons 3H trace 12.32 y β− 0.019 3He
References
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Hydrogen (pronounced /ˈhaɪdrədʒən/^[1]) is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H₂. With an atomic mass of 1.00794 amu, hydrogen is the lightest element. Depiction of a hydrogen atom showing the diameter as about twice the Bohr model radius. ... Look up hydrogen in Wiktionary, the free dictionary. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... This article is about the chemical element. ... Image File history File links H-TableImage. ... This is a standard display of the periodic table of the elements. ... An extended periodic table was suggested by Glenn T. Seaborg in 1969. ... This is a list of chemical elements, sorted by name and color coded according to type of element. ... Categories: Chemical elements ... sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex sex... Together with the metals and metalloids, a nonmetal is one of three categories of chemical elements as distinguished by ionization and bonding properties. ... A group, also known as a family, is a vertical column in the periodic table of the chemical elements. ... In the periodic table of the elements, a period is a horizontal row of the table. ... A block of the periodic table of elements is a set of adjacent groups. ... The alkali metals are a chemical series. ... A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the elements. ... The s-block of the periodic table of elements consists of the first two groups: the alkali metals and alkaline earth metals, plus hydrogen. ... Color is an important part of the visual arts. ... Hydrogen sample (gas, doesnt look like much). ... The atomic mass (ma) is the mass of an atom at rest, most often expressed in unified atomic mass units. ... To help compare different orders of magnitude, the following list describes various mass levels between 10−36 kg and 1053 kg. ... Hydrogen = 1 List of Elements in Atomic Number Order. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ... Electron atomic and molecular orbitals In atomic physics and quantum chemistry, the electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure (, a crystal). ... For other uses, see Electron (disambiguation). ... Example of a sodium electron shell model An electron shell, also known as a main energy level, is a group of atomic orbitals with the same value of the principal quantum number n. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... For other uses, see Gas (disambiguation). ... For other uses, see Density (disambiguation). ... The melting point of a solid is the temperature range at which it changes state from solid to liquid. ... For other uses, see Kelvin (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Fahrenheit (disambiguation). ... Italic text This article is about the boiling point of liquids. ... For other uses, see Kelvin (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Fahrenheit (disambiguation). ... In physics, the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium. ... For other uses, see Celsius (disambiguation). ... In physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions (temperature, pressure) at which the liquid state of the matter ceases to exist. ... For other uses, see Kelvin (disambiguation). ... Standard enthalpy change of fusion of period three. ... Kilojoule per mole are an SI derived unit of energy per amount of material, where energy is measured in units of 1000 joules, and the amount of material is measured in mole units. ... The heat of vaporization is a physical property of substances. ... Kilojoule per mole are an SI derived unit of energy per amount of material, where energy is measured in units of 1000 joules, and the amount of material is measured in mole units. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... Not to be confused with oxidation state. ... In chemistry, an amphoteric substance is one that can react with either an acid or base (more generally, the word describes something made of, or acting like, two components). ... Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. ... Kilojoule per mole are an SI derived unit of energy per amount of material, where energy is measured in units of 1000 joules, and the amount of material is measured in mole units. ... Atomic radius: Ionic radius Covalent radius Metallic radius van der Waals radius edit Atomic radius, and more generally the size of an atom, is not a precisely defined physical quantity, nor is it constant in all circumstances. ... To help compare different orders of magnitude this page lists lengths between 10 pm and 100 pm (10-11 m and 10-12 m). ... One picometre is defined as 1x10-12 metres, in standard units. ... To help compare different orders of magnitude this page lists lengths between 10 pm and 100 pm (10-11 m and 10-12 m). ... Atomic radius: Ionic radius Covalent radius Metallic radius van der Waals radius edit The covalent radius, rcov, is a measure of the size of atom which forms part of a covalent bond. ... To help compare different orders of magnitude this page lists lengths between 10 pm and 100 pm (10-11 m and 10-12 m). ... The van der Waals radius of an atom is the radius of an imaginary hard sphere which can be used to model the atom for many purposes. ... You have big harry skanky balls ... K value redirects here. ... This page is about the physical speed of sound waves in a medium. ... Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... Hydrogen (H) Standard atomic mass: 1. ... For other uses, see Isotope (disambiguation). ... Natural abundance refers to the prevalence of different isotopes of an element as found in nature. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... In physics, the decay mode describes a particular way a particle decays. ... The decay energy is the energy released by a nuclear decay. ... The electronvolt (symbol eV) is a unit of energy. ... In nuclear physics, a decay product, also known as a daughter product, is a nuclide resulting from the radioactive decay of a parent or precursor nuclide. ... Stable isotopes are chemical isotopes that are not radioactive. ... This article or section does not adequately cite its references or sources. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ... Stable isotopes are chemical isotopes that are not radioactive. ... This article or section does not adequately cite its references or sources. ... Tritium (symbol T or ³H) is a radioactive isotope of hydrogen. ... A trace radioisotope is a radioisotope that is naturally occurring. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Recommended values for many properties of the elements, together with various references, are collected on these data pages. ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... See also: List of elements by atomic number In chemistry and physics, the atomic number (also known as the proton number) is the number of protons found in the nucleus of an atom. ... Temperature and air pressure can vary from one place to another on the Earth, and can also vary in the same place with time. ... Together with the metals and metalloids, a nonmetal is one of three categories of chemical elements as distinguished by ionization and bonding properties. ... This article is about the chemical reaction combustion. ... A space-filling model of the diatomic molecule dinitrogen, N2. ... For other uses, see Gas (disambiguation). ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... Stylized lithium-7 atom: 3 protons, 4 neutrons & 3 electrons (~1800 times smaller than protons/neutrons). ...

Hydrogen is the most abundant of the chemical elements, constituting roughly 75% of the universe's elemental mass.^[2] Stars in the main sequence are mainly composed of hydrogen in its plasma state. Elemental hydrogen is relatively rare on Earth, and is industrially produced from hydrocarbons such as methane, after which most elemental hydrogen is used "captively" (meaning locally at the production site), with the largest markets about equally divided between fossil fuel upgrading (e.g., hydrocracking) and ammonia production (mostly for the fertilizer market). Hydrogen may be produced from water using the process of electrolysis, but this process is presently significantly more expensive commercially than hydrogen production from natural gas.^[3] The abundance of a chemical element measures how relatively common the element is, or how much of the element there is by comparison to all other elements. ... This article is about the astronomical object. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... For other uses, see Plasma. ... This article is about Earth as a planet. ... Look up Hydrocarbon in Wiktionary, the free dictionary. ... Fossil fuels or mineral fuels are fossil source fuels, that is, hydrocarbons found within the top layer of the earth’s crust. ... In petroleum geology and chemistry, cracking is the process whereby complex organic molecules (e. ... For other uses, see Ammonia (disambiguation). ... In chemistry and manufacturing, electrolysis is a method of separating chemically bonded elements and compounds by passing an electric current through them. ...

The most common naturally occurring isotope of hydrogen, known as protium, has a single proton and no neutrons. In ionic compounds it can take on either a positive charge (becoming a cation composed of a bare proton) or a negative charge (becoming an anion known as a hydride). Hydrogen can form compounds with most elements and is present in water and most organic compounds. It plays a particularly important role in 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. For other uses, see Isotope (disambiguation). ... A hydrogen atom is an atom of the element hydrogen. ... For other uses, see Proton (disambiguation). ... This article or section does not adequately cite its references or sources. ... The crystal structure of sodium chloride, NaCl, a typical ionic compound. ... This article is about the electrically charged particle. ... This article is about the electrically charged particle. ... Hydride is the name given to the negative ion of hydrogen, H−. Although this ion does not exist except in extraordinary conditions, the term hydride is widely applied to describe compounds of hydrogen with other elements, particularly those of groups 1–16. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. ... Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Mineral acids Organic acids Bases: Strong bases Weak bases Organic bases edit An acid-base reaction is a chemical reaction between an acid and a... This box:      For a non-technical introduction to the topic, please see Introduction to quantum mechanics. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ...

[edit] Chemistry and characteristics

The solubility and characteristics of hydrogen with various metals are very important in metallurgy (as many metals can suffer hydrogen embrittlement^[4]) and in developing safe ways to store it for use as a fuel.^[5] Hydrogen is highly soluble in many compounds composed of rare earth metals and transition metals^[6] and can be dissolved in both crystalline and amorphous metals.^[7] Hydrogen solubility in metals is influenced by local distortions or impurities in the metal crystal lattice.^[8] Solubility is a chemical property referring to the ability for a given substance, the solute, to dissolve in a solvent. ... The word characteristic has several meanings: In mathematics, see characteristic (algebra) characteristic function characteristic subgroup Euler characteristic method of characteristics In genetics, see characteristic (genetics). ... Georg Agricola, author of De re metallica, an important early book on metal extraction Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their compounds, which are called alloys. ... Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and crack following exposure to hydrogen. ... Rare earth ore Rare earth elements and rare earth metals are trivial names sometimes applied to a collection of 17 chemical elements in the periodic table, namely scandium, yttrium, and the lanthanides. ... In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: It commonly refers to any element in the d-block of the periodic table, including zinc, cadmium and mercury. ... Crystal (disambiguation) Insulin crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... Wax and paraffin are amorphous. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ...

[edit] Combustion

Hydrogen is highly combustible in air. It burned rapidly in the Hindenburg disaster on May 6, 1937.

Hydrogen gas is highly flammable and will burn at concentrations as low as 4% H₂ in air.^[9] The enthalpy of combustion for hydrogen is −286 kJ/mol;^[10] it burns according to the following balanced equation. Image File history File links Hindenburg_burning. ... Image File history File links Hindenburg_burning. ... LZ 129 Hindenburg was a German zeppelin. ... is the 126th day of the year (127th in leap years) in the Gregorian calendar. ... Year 1937 (MCMXXXVII) was a common year starting on Friday (link will display the full calendar) of the Gregorian calendar. ... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ...

2 H₂(g) + O₂(g) → 2 H₂O(l) + 572  kJ (286 kJ/mol)^[11]

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.^[12] 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 SRBs). Thus it is difficult to visually detect if a hydrogen leak is burning. The explosion of the Hindenburg airship was an infamous case of hydrogen combustion (pictured); the cause is debated, but combustible materials in the ship's skin were responsible for the coloring of the flames.^[13] Another characteristic of hydrogen fires is that the flames tend to ascend rapidly with the gas in air, as illustrated by the Hindenburg flames, causing less damage than hydrocarbon fires. Two-thirds of the Hindenburg passengers survived the fire, and many of the deaths which occurred were from falling or from diesel fuel burns.^[14] For other uses, see Ultraviolet (disambiguation). ... This article is about the space vehicle. ... The Space Shuttle Solid Rocket Booster (SRB) is the rocket that provides 83% of liftoff thrust for the Space Shuttle. ... LZ 129 Hindenburg was a German zeppelin. ...

H₂ reacts directly with other oxidizing elements. A violent and spontaneous reaction can occur at room temperature with chlorine and fluorine, forming the corresponding hydrogen halides: hydrogen chloride and hydrogen fluoride.^[15] General Name, symbol, number chlorine, Cl, 17 Chemical series nonmetals Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... Distinguished from fluorene and fluorone. ... R-phrases , S-phrases , , , , Flash point non-flammable Supplementary data page Structure and properties n, εr, etc. ... Hydrogen fluoride is a chemical compound with the formula HF. Together with hydrofluoric acid, it is the principal industrial source of fluorine and hence the precursor to many important compounds including pharmaceuticals and polymers (e. ...

[edit] Electron energy levels

Main article: Hydrogen atom

Depiction of a hydrogen atom showing the diameter as about twice the Bohr model radius (image not to scale).

The ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 92 nm.^[16] Depiction of a hydrogen atom showing the diameter as about twice the Bohr model radius. ... Image File history File links Hydrogen_atom. ... Image File history File links Hydrogen_atom. ... The Bohr model of the hydrogen atom () or a hydrogen-like ion (), where the negatively charged electron confined to an atomic shell encircles a small positively charged atomic nucleus, and an electron jump between orbits is accompanied by an emitted or absorbed amount of electromagnetic energy . ... In physics, the ground state of a quantum mechanical system is its lowest-energy state. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... The electronvolt (symbol eV) is a unit of energy. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... This article is about the unit of length. ...

The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, which conceptualizes the electron as "orbiting" the proton in analogy to the Earth's orbit of the sun. However, the electromagnetic force attracts electrons and protons to one another, while planets and celestial objects are attracted to each other by gravity. Because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies.^[17] The Bohr model of the hydrogen atom () or a hydrogen-like ion (), where the negatively charged electron confined to an atomic shell encircles a small positively charged atomic nucleus, and an electron jump between orbits is accompanied by an emitted or absorbed amount of electromagnetic energy . ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... Gravity is a force of attraction that acts between bodies that have mass. ... This gyroscope remains upright while spinning due to its angular momentum. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ...

A more accurate description of the hydrogen atom comes from a purely quantum mechanical treatment that uses the Schrödinger equation or the equivalent Feynman path integral formulation to calculate the probability density of the electron around the proton.^[18] This box:      For a non-technical introduction to the topic, please see Introduction to quantum mechanics. ... Richard Feynman Richard Phillips Feynman (May 11, 1918–February 15, 1988) (surname pronounced FINE-man) was one of the most influential American physicists of the 20th century, expanding greatly the theory of quantum electrodynamics. ... This article or section is in need of attention from an expert on the subject. ... In quantum mechanics, a probability amplitude is a complex-valued function that describes an uncertain or unknown quantity. ...

[edit] Elemental molecular forms

First tracks observed in liquid hydrogen bubble chamber at the Bevatron

There are two different types of diatomic hydrogen molecules that differ by the relative spin of their nuclei.^[19] In the orthohydrogen form, the spins of the two protons are parallel and form a triplet state; 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".^[20] 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.^[21] The ortho/para distinction also occurs in other hydrogen-containing molecules or functional groups, such as water and methylene.^[22] Download high resolution version (640x852, 62 KB)First tracks observed in liquid hydrogen bubble chamber by John Wood, 1954. ... Download high resolution version (640x852, 62 KB)First tracks observed in liquid hydrogen bubble chamber by John Wood, 1954. ... A bubble chamber A bubble chamber is a vessel filled with a superheated transparent liquid used to detect electrically charged particles moving through it. ... Edwin McMillan and Edward Lofgren on the shielding of the Bevatron. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... Orthohydrogen and Parahydrogen An hydrogen molecule is made up of two atoms of hydrogen linked by a covalent bond. ... Orthohydrogen and Parahydrogen An hydrogen molecule is made up of two atoms of hydrogen linked by a covalent bond. ... After absorbing energy, an electron may jump from the ground state to a higher energy excited state. ... In chemistry, methylene is a divalent functional group CH2 derived formally from methane. ...

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.^[23] 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 exothermic and produces enough heat to evaporate the hydrogen liquid, leading to loss of the liquefied material. Catalysts for the ortho-para interconversion, such as iron compounds, are used during hydrogen cooling.^[24] In thermodynamics, the word exothermic outside heating describes a process or reaction that releases energy usually in the form of heat, but it can also release energy in form of light (e. ... It has been suggested that this article or section be merged into Catalysis. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ...

A molecular form called protonated molecular hydrogen, or H₃⁺, is found in the interstellar medium (ISM), where it is generated by ionization of molecular hydrogen from 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.^[25] Protonated molecular hydrogen, or H3+, is one of the most abundant ions in the universe. ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... For other uses, see Jupiter (disambiguation). ...

[edit] Mono-atomic form

H atoms, also called nascent hydrogen or atomic hydrogen, are claimed to exist transiently but long enough to effect chemical reactions. According to one claim, nascent hydrogen is generated in situ usually by the reaction of zinc with an acid, or by electrolysis at the cathode. Being monoatomic, H atoms are much more reactive and thus a much more effective reducing agent than ordinary diatomic H₂, but again the key question is whether H atoms exist in any chemically meaningful way under the conditions claimed. The concept is more popular in engineering and in older literature on catalysis. In situ is a Latin phrase meaning in the place. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... For other uses, see acid (disambiguation). ... In chemistry and manufacturing, electrolysis is a method of separating chemically bonded elements and compounds by passing an electric current through them. ... Diagram of a copper cathode in a Daniells cell. ... A reducing agent (also called a reductant or reducer) is the element or a compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species. ...

Nascent hydrogen is claimed to reduce nitrites to ammonia, or arsenic to arsine even under mild conditions. Detailed scrutiny of such claims usually points alternative pathways, not H atoms. // Definition The nitrite ion is NO2−. A nitrite compound is one that contains this group, either an ionic compound, or an analogous covalent one. ... For other uses, see Ammonia (disambiguation). ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... Arsine, the simplest compound of arsenic, is AsH3. ...

Atomic hydrogen can be formed at temperatures high enough (> 2000 K) to thermally dissociate the molecule, or equivalent excitation in an electric discharge. Also, electromagnetic radiation above about 11 ev can be absorbed by H₂ and lead to its dissociation. a localised surplus of electrons migrates from the negative pole to the positive pole to overcome its unfavourable energetic condition. ... The electronvolt (symbol eV) is a unit of energy. ...

It takes 4.476 eV to disassociate ordinary H₂ hydrogen molecules. When they recombine, they liberate this energy. The atomic hydrogen torch uses this to generate very high temperatures near 4,000°C for welding. Hydrogen is a powerful reducing agent which eliminates the need for flux to prevent oxidation of the weld. Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... A reducing agent (also called a reductant or reducer) is the element or a compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species. ... In metallurgy, flux is a substance which removes passivating oxides from the surface of a metal or alloy. ...

Occasionally, hydrogen chemisorbed on metal surfaces is referred to as "nascent", although this terminology is fading with time. Other views hold that such chemisorbed hydrogen is "a bit less reactive than nascent hydrogen because of the bonds provided by the catalyst metal surface." Also, such catalyst provided atoms are not called nascent hydrogen, because they don't need to be captured and reacted in their instanteneous, temporary, "just generated" state, because the catalyst is able to reversibly generate them from the hydrogen gas supply at any time.

Atomic hydrogen determines the frequency of hydrogen masers which are used as precise frequency standards. They operate at the 1420 MHz frequency corresponding to an absorption line in atomic hydrogen. In telecommunication, a frequency standard is a stable oscillator used for frequency calibration or reference. ... For other uses, see Frequency (disambiguation). ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ...

NASA has investigated the use of atomic hydrogen as a rocket propellant. It could be stored in liquid helium to prevent it from recombining into molecular hydrogen. When the helium is vaporized, the atomic hydrogen would be released and combine back to molecular hydrogen. The result would be a intensely hot stream of hydrogen and helium gas. The liftoff weight of rockets could be reduced by 50% by this method.^[26] For other uses, see NASA (disambiguation). ... Rocket propellants undergo exothermic chemical reactions which produce hot gas which is used by a rocket for propulsive purposes. ...

Most interstellar hydrogen is in the mono-atomic form because the atoms can seldom collide and combine. They are the source of the important 21cm hydrogen line in astronomy at 1420 MHz. ^[27] The interstellar medium (or ISM) is a term used in astronomy to describe the rarefied gas and dust that exists between the stars (or their immediate circumstellar environment) within a galaxy. ... This article or section does not adequately cite its references or sources. ... For other uses, see Astronomy (disambiguation). ...

[edit] Compounds

Further information: Hydrogen compounds

[edit] Covalent and organic compounds

While H₂ is not very reactive under standard conditions, it does form compounds with most elements. Millions of hydrocarbons are known, but they are not formed by the direct reaction of elementary hydrogen and carbon (although synthesis gas production followed by the Fischer-Tropsch process to make hydrocarbons comes close to being an exception, as this begins with coal and the elemental hydrogen is generated in situ).^{[citation needed]} Hydrogen can form compounds with elements that are more electronegative, such as halogens (e.g., F, Cl, Br, I); in these compounds hydrogen takes on a partial positive charge.^[28] When bonded to fluorine, oxygen, or nitrogen, hydrogen can participate in a form of strong noncovalent bonding called hydrogen bonding, which is critical to the stability of many biological molecules.^[29][30] Hydrogen also forms compounds with less electronegative elements, such as the metals and metalloids, in which it takes on a partial negative charge. These compounds are often known as hydrides.^[31] Look up Hydrocarbon in Wiktionary, the free dictionary. ... Syngas (from synthesis gas) is the name given to gasses of varying composition that are generated in coal gasification and some types of waste-to-energy facilities. ... // The Fischer-Tropsch process is a catalyzed chemical reaction in which carbon monoxide and hydrogen are converted into liquid hydrocarbons of various forms. ... It has been suggested that this article or section be merged with electronegativity. ... This article is about the chemical series. ... Distinguished from fluorene and fluorone. ... This article is about the chemical element and its most stable form, or dioxygen. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... An example of a quadruple hydrogen bond between a self-assembled dimer complex reported by Meijer and coworkers. ... This article is about metallic materials. ... Metalloid is a term used in chemistry when classifying the chemical elements. ... Hydride is the name given to the negative ion of hydrogen, H−. Although this ion does not exist except in extraordinary conditions, the term hydride is widely applied to describe compounds of hydrogen with other elements, particularly those of groups 1–16. ...

Hydrogen forms a vast array of compounds with carbon. Because of their general association with living things, these compounds came to be called organic compounds;^[32] the study of their properties is known as organic chemistry^[33] and their study in the context of living organisms is known as biochemistry.^[34] By some definitions, "organic" compounds are only required to contain carbon. 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.^[32] For other uses, see Carbon (disambiguation). ... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. ... Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting primarily of carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, the halogens as... Domains and Kingdoms Nanobes Acytota Cytota Bacteria Neomura Archaea Eukaryota Bikonta Apusozoa Rhizaria Excavata Archaeplastida Rhodophyta Glaucophyta Plantae Heterokontophyta Haptophyta Cryptophyta Alveolata Unikonta Amoebozoa Opisthokonta Choanozoa Fungi Animalia An ericoid mycorrhizal fungus Life on Earth redirects here. ... Wöhler observes the synthesis of urea. ...

In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is particularly common in group 13 elements, especially in boranes (boron hydrides) and aluminium complexes, as well as in clustered carboranes.^[35] Inorganic chemistry is the branch of chemistry concerned with the properties and reactions of inorganic compounds. ... A bridging ligand is essentially a ligand that acts as a bridge connecting two metal centres in a complex. ... Synthesis of copper(II)-tetraphenylporphine, a metal complex, from tetraphenylporphine and copper(II) acetate monohydrate. ... The Boron group is periodic table group 13 (IUPAC style) in the periodic table. ... In chemistry a borane is a chemical compound of boron and hydrogen. ... For other uses, see Boron (disambiguation). ... Aluminum redirects here. ... 3D model of carborane acid, colors: Hydrogen - white, Chlorine - yellow, Boron - green, Carbon - black A carborane is a cluster composed of boron and carbon atoms. ...

[edit] Hydrides

Compounds of hydrogen are often called hydrides, a term that is used fairly loosely. To chemists, the term "hydride" usually implies that the H atom has acquired a negative or anionic character, denoted H⁻. The existence of the hydride anion, suggested by Gilbert N. Lewis in 1916 for group I and II salt-like hydrides, was demonstrated by Moers in 1920 with the electrolysis of molten lithium hydride (LiH), that produced a stoichiometric quantity of hydrogen at the anode.^[36] For hydrides other than group I and II metals, the term is quite misleading, considering the low electronegativity of hydrogen. An exception in group II 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, there are over 100 binary borane hydrides known, but only one binary aluminium hydride.^[37] Binary indium hydride has not yet been identified, although larger complexes exist.^[38] Hydride is the name given to the negative ion of hydrogen, H−. Although this ion does not exist except in extraordinary conditions, the term hydride is widely applied to describe compounds of hydrogen with other elements, particularly those of groups 1–16. ... Lewis in the Berkeley Lab Gilbert Newton Lewis (October 23, 1875-March 23, 1946) was a famous American physical chemist. ... Ionic lattice structure of lithium hydride Lithium hydride (LiH) is the compound of lithium and hydrogen. ... In chemistry, stoichiometry is the study of the combination of elements in chemical reactions. ... Lithium aluminium hydride (LiAlH4), commonly abbreviated to LAH, is a powerful reducing agent used in organic chemistry. ... General Name, Symbol, Number indium, In, 49 Chemical series poor metals Group, Period, Block 13, 5, p Appearance silvery lustrous gray Standard atomic weight 114. ...

[edit] Protons and acids

See also: Acid-base reaction

Oxidation of H₂ formally gives the proton, H⁺. This species is central to discussion of acids. Under the Bronsted-Lowry theory, acids are proton donors, while bases are proton acceptors. Acids and bases: Acid-base reaction pH Self-ionization of water Buffer solutions Systematic naming Acid-base extraction Acidity function Proton affinity Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit is a chemical reaction that... For other uses, see Proton (disambiguation). ... For other uses, see acid (disambiguation). ... An acid-base reaction is a chemical reaction between an acid and a base. ...

A bare proton H⁺ cannot exist in solution because of its strong tendency to attach itself to atoms or molecules with electrons. However, the term 'proton' is used loosely to refer to positively charged or cationic hydrogen, denoted H⁺. A cation is an ion with positive charge. ...

To avoid the convenient fiction of the naked "solvated proton" in solution, acidic aqueous solutions are sometimes considered to contain the hydronium ion (H₃O⁺), which is organized into clusters to form H₉O₄⁺.^[39] Other oxonium ions are found when water is in solution with other solvents.^[40] In chemistry, hydronium is the common name for the cation H3O+ derived from protonation of water. ...

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.^[41] Protonated molecular hydrogen, or H3+, is one of the most abundant ions in the universe. ...

[edit] Isotopes

Main article: Isotopes of hydrogen

Protium, the most common isotope of hydrogen, has one proton and one electron. Unique among all stable isotopes, it has no neutrons (see diproton for discussion of why others do not exist).

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.^[42][43] Hydrogen (H) Standard atomic mass: 1. ... Image File history File links Hydrogen. ... Image File history File links Hydrogen. ... A diproton is a hypothetical type of helium nucleus consisting of two protons and no neutrons. ...

• ¹H is the most common hydrogen isotope with an abundance of more than 99.98%. Because the nucleus of this isotope consists of only a single proton, it is given the descriptive but rarely used formal name protium.^[44]
• ²H, the other stable hydrogen isotope, is known as deuterium and contains one proton and one neutron in its nucleus. Deuterium is not radioactive, and does not represent a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for ¹H-NMR spectroscopy.^[45] Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial nuclear fusion.^[46]
• ³H is known as tritium and contains one proton and two neutrons in its nucleus. It is radioactive, decaying into Helium-3 through beta decay with a half-life of 12.32 years.^[35] Small amounts of tritium occur naturally because of the interaction of cosmic rays with atmospheric gases; tritium has also been released during nuclear weapons tests.^[47] It is used in nuclear fusion reactions,^[48] as a tracer in isotope geochemistry,^[49] and specialized in self-powered lighting devices.^[50] Tritium has also been used in chemical and biological labeling experiments as a radiolabel.^[51]

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.^[52] In its nomenclatural guidelines, the International Union of Pure and Applied Chemistry allows any of D, T, ²H, and ³H to be used, although ²H and ³H are preferred.^[53] The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... For other uses, see Proton (disambiguation). ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ... This article or section does not adequately cite its references or sources. ... Heavy water is dideuterium oxide, or D2O or 2H2O. It is chemically the same as normal water, H2O, but the hydrogen atoms are of the heavy isotope deuterium, in which the nucleus contains a neutron in addition to the proton found in the nucleus of any hydrogen atom. ... Nuclear magnetic resonance spectroscopy most commonly known as NMR spectroscopy is the name given to the technique which exploits the magnetic properties of certain nuclei. ... This does not cite any references or sources. ...