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Key People:Henry CavendishAntoine LavoisierOtto StruveAnders Jonas ÅngströmFritz Wolfgang London...(Show more)Related Topics:HydrideDeuteriumAirTritiumProtium...(Show more)

hydrogen (H), a colourless, odourless, tasteless, flammable gas substance the is the most basic member that the family of chemical elements. The hydrogen atom has a cell nucleus consisting that a proton bearing one unit the positive electrical charge; one electron, bearing one unit of negative electrical charge, is additionally associated v this nucleus. Under simple conditions, hydrogen gas is a loose aggregation that hydrogen molecules, each consisting of a pair of atoms, a diatomic molecule, H2. The earliest known vital chemical building of hydrogen is the it burns v oxygen to type water, H2O; indeed, the surname hydrogen is acquired from Greek words definition “maker that water.”

Although hydrogen is the most abundant element in the universe (three times as abundant as helium, the next many widely arising element), it renders up only around 0.14 percent of earth crust through weight. It occurs, however, in vast quantities as component of the water in oceans, ice packs, rivers, lakes, and also the atmosphere. As part of innumerable carbon compounds, hydrogen is current in all animal and also vegetable tissue and also in petroleum. Even though the is frequently said that there are an ext known compounds of carbon 보다 of any other element, the truth is that, since hydrogen is consisted of in nearly all carbon compounds and likewise forms a multitude that compounds v all other elements (except several of the noble gases), the is feasible that hydrogen compound are much more numerous.


Elementary hydrogen find its principal commercial application in the to produce of ammonia (a compound of hydrogen and nitrogen, NH3) and in the hydrogenation that carbon monoxide and also organic compounds.

Hydrogen has three known isotopes. The mass numbers of hydrogen’s isotopes are 1, 2, and also 3, the many abundant being the massive 1 isotope generally dubbed hydrogen (symbol H, or 1H) but additionally known as protium. The massive 2 isotope, which has a cell core of one proton and also one neutron and also has been called deuterium, or heavy hydrogen (symbol D, or 2H), constitutes 0.0156 percent of the simple mixture of hydrogen. Tritium (symbol T, or 3H), v one proton and two neutrons in each nucleus, is the fixed 3 isotope and constitutes around 10−15 to 10−16 percent that hydrogen. The practice of giving unique names come the hydrogen isotope is justified by the fact that there are far-ranging differences in their properties.

Paracelsus, physician and alchemist, in the 16th century unknowingly experimented v hydrogen once he found that a flammable gas was developed when a steel was dissolved in acid. The gas, however, was confused with various other flammable gases, such as hydrocarbons and carbon monoxide. In 1766 Henry Cavendish, English chemist and also physicist, showed that hydrogen, then dubbed flammable air, phlogiston, or the flammable principle, was distinctive from various other combustible gases since of the density and also the quantity of the that progressed from a offered amount the acid and metal. In 1781 Cavendish shown previous monitorings that water was formed when hydrogen to be burned, and also Antoine-Laurent Lavoisier, the father of contemporary chemistry, coined the French indigenous hydrogène indigenous which the English type is derived. In 1929 karl Friedrich Bonhoeffer, a German physical chemist, and Paul Harteck, one Austrian chemist, top top the communication of earlier theoretical work, confirmed that simple hydrogen is a mixture of 2 kinds of molecules, ortho-hydrogen and para-hydrogen. Due to the fact that of the basic structure that hydrogen, its properties can be about theory calculated fairly easily. Thus hydrogen is regularly used as a theoretical version for more complex atoms, and also the results are applied qualitatively to other atoms.

Physical and also chemical properties

The Table list the crucial properties of molecule hydrogen, H2. The very low melting and also boiling points result from weak pressures of attraction between the molecules. The existence of this weak intermolecular pressures is likewise revealed by the reality that, as soon as hydrogen gas increases from high come low press at room temperature, that is temperature rises, whereas the temperature of many other gases falls. According to thermodynamic principles, this suggests that repulsive forces exceed attractive forces between hydrogen molecule at room temperature—otherwise, the expansion would cool the hydrogen. In fact, in ~ −68.6° C attractive forces predominate, and hydrogen, therefore, cools top top being enabled to expand listed below that temperature. The cooling impact becomes for this reason pronounced in ~ temperatures listed below that of fluid nitrogen (−196° C) that the effect is made use of to attain the liquefaction temperature the hydrogen gas itself.

some properties of normal hydrogen and also deuterium regular hydrogen deuterium atomic hydrogen molecule hydrogen
atomic number 1 1
atomic weight 1.0080 2.0141
ionization potential 13.595 electron volts 13.600 electron volts
electron affinity 0.7542 electron volts 0.754 electron volts
nuclear spin 1/2 1
nuclear magnetic minute (nuclear magnetons) 2.7927 0.8574
nuclear quadrupole minute 0 2.77(10−27) square centimetres
electronegativity (Pauling) 2.1 ~2.1
bond street 0.7416 angstrom 0.7416 angstrom
dissociation power (25 levels C) 104.19 kilocalories per mole 105.97 kilocalories per mole
ionization potential 15.427 electron volts 15.457 electron volts
thickness of solid 0.08671 gram per cubic centimetre 0.1967 gram every cubic centimetre
melting suggest −259.20 degrees Celsius −254.43 degrees Celsius
warm of combination 28 calories every mole 47 calories per mole
thickness of fluid 0.07099 (−252.78 degrees) 0.1630 (−249.75 degrees)
boiling point −252.77 levels Celsius −249.49 degrees Celsius
warm of vaporization 216 calories per mole 293 calories every mole
an essential temperature −240.0 levels Celsius −243.8 degrees Celsius
critical pressure 13.0 settings 16.4 settings
an important density 0.0310 gram per cubic centimetre 0.0668 gram per cubic centimetre
warm of burning to water (g) −57.796 kilocalories per mole −59.564 kilocalories every mole

Hydrogen is transparent to visible light, come infrared light, and also to ultraviolet light to wavelengths below 1800 Å. Due to the fact that its molecular weight is lower than the of any other gas, that is molecules have actually a velocity higher than those of any type of other gas in ~ a given temperature and it diffuses quicker than any type of other gas. Consequently, kinetic power is dispersed faster through hydrogen 보다 through any other gas; the has, for example, the greatest heat conductivity.

A molecule that hydrogen is the simplest possible molecule. It consists of two protons and two electrons held together through electrostatic forces. Prefer atomic hydrogen, the assemblage deserve to exist in a number of energy levels.

Ortho-hydrogen and para-hydrogen

Two types of molecule hydrogen (ortho and also para) are known. These differ in the magnetic interaction of the protons because of the spinning activities of the protons. In ortho-hydrogen, the spins of both protons room aligned in the same direction—that is, they room parallel. In para-hydrogen, the spins space aligned in opposite directions and are thus antiparallel. The connection of rotate alignments determines the magnetic properties of the atoms. Normally, changes of one kind into the other (i.e., conversions in between ortho and also para molecules) execute not occur and also ortho-hydrogen and also para-hydrogen deserve to be related to as 2 distinct adjustments of hydrogen. The two forms may, however, interconvert under specific conditions. Equilibrium in between the two forms can be established in number of ways. One of these is through the development of catalysts (such as caused charcoal or miscellaneous paramagnetic substances); another an approach is to apply an electric discharge to the gas or to warmth it to a high temperature.

The concentration that para-hydrogen in a mixture that has completed equilibrium in between the two forms depends on the temperature as presented by the complying with figures:


Essentially pure para-hydrogen can be created by happen the mixture into call with charcoal in ~ the temperature of fluid hydrogen; this converts all the ortho-hydrogen into para-hydrogen. The ortho-hydrogen, on the various other hand, can not be prepared directly from the mixture because the concentration that para-hydrogen is never less than 25 percent.

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The two develops of hydrogen have slightly various physical properties. The melting allude of para-hydrogen is 0.10° lower than the of a 3:1 mixture that ortho-hydrogen and also para-hydrogen. In ~ −252.77° C the push exerted by the vapour over liquid para-hydrogen is 1.035 atmospheres (one atmosphere is the press of the setting at sea level under typical conditions, equal to about 14.69 pounds per square inch), contrasted with 1.000 atmosphere for the vapour press of the 3:1 ortho–para mixture. Together a an outcome of the various vapour pressures of para-hydrogen and ortho-hydrogen, these develops of hydrogen have the right to be separated by low-temperature gas chromatography, an analytical procedure that separates different atomic and molecular types on the basis of your differing volatilities.