On Earth and except the compounds with other atoms, the molecule of hydrogen generally appears as an element Gaz them: the Dihydrogène (H), often called simply “hydrogen”. Hydrogen is present in many Molécule S: Water, Sugar, Protein S, Hydrocarbon S.
Surprisingly, hydrogen is a Métal: when it is in solid form (very high Pression S and very low Température S), it crystallizes with a metal Liaison (see metal Hydrogène). In the periodic Table of the elements, it is besides in the column of the alkaline metals. Not being present at the solid state on Earth, he however is not regarded as a metal in chemistry. In a simplistic way its metal nature is due to its outer-shell electron on its single and last saturated layer with two electrons.
Principal characteristicsHydrogen is the the chemical element simplest; its most common Isotope is only made up of a Proton and a electron. So it is a univalent atom . The mass of the electron being negligible in front of those of the protons and the neutrons, these are the latter which determine the mass of the atoms (thus their weight). Hydrogen is thus lightest existing Atome.
On Earth and except the compounds with other atoms, it is generally appeared as a Gaz: the Dihydrogène. Under very low pressures, as those which exist in the space, hydrogen tends to exist in the form of individual atoms, simply because it is then improbable that they enter in collision to combine. Always in space, the clouds of H are at the base of the process of the formation of the stars (compression of gases).
This element plays a vital part in the Univers via the reactions proton-proton and of the Cycle of Bethe (cycle catalytic CNO: carbon-nitrogenize-oxygen), which is two ways of reactions of thermonuclear Fusion which create enormous quantities of energy by combining four hydrogen atoms to form an atom of Hélium.
Broad quantities of hydrogen necessary in industry, in particular in the are proceeded Haber-Bosch of production of the Ammoniac, the Hydrogénation of the grease S and the Huile S and the production of Méthanol. Other uses of hydrogen are:
- the manufacture of the Hydrochloric acid , the Welding, the Fuel S for rocket S and the Reduction of metal Ore S;
- liquid hydrogen (LH2) is used for research at very low temperatures, including the study of the Supraconductivité;
- hydrogen was used in the balloon S because it is fourteen times lighter than the air.
- the Deuterium ( 2 H) is used in the nuclear applications as Modérateur to slow down the Neutron S. the compounds of deuterium are also used in Chimie and Biologie to study or use the isotopic Effet;
- the Tritium ( 3 H), another isotope, are produced in the nuclear reactors and are used for the construction of atomic bombs. It is also used like an isotopic marker in the biosciences and like source of radiation in luminescent paintings.
- the hydrogen or rather of nitrogen hydrogenated is also used like tracer gas to carry out research operations of microphone-escapes in industrial units (automobile, capital equipment, heating installation, water distribution network, tank of planes, etc…).
Hydrogen like vector of energy
See also: hydrogen Economy
Hydrogen is regularly quoted like vector of energy with a future. It is not of the hydrogen element but the dihydrogene, which is a “clean” fuel in the direction where its combustion generates only steam, but which is not present in the atmosphere safe at the state of traces (it is thus necessary to take into account the pollution generated by the manufacture of dihydrogene). It thus is not about an energy source primary, or fossil, but of a means of storage of energy, like a battery. Hydrogen causes many hopes because it would bring an answer to two of the energy main challenges of the 21e century:
- the progressive exhaustion of the nonrenewable energy sources;
- the gas emission with Greenhouse effect by the energy sources used currently, the combustion of the releasing hydrogen only of water.
Claude Mandil, executive director of the International agency of energy, estimates thus that hydrogen will have “to play a crucial role” in the worldwide economy. Many experiments were undertaken in the field of the clean Véhicules. Chrysler - BMW has a fleet of cars (thermal engine) rolling to hydrogen H, without combustible battery, with cryogenic tank. Several European countries subsidize programmes of use of hydrogen in public transport.
However the production, the storage and the transport of hydrogen still pose many technological problems, so that its use of mass is not currently possible:
- cost of the combustible batteries: they are equipped with foam of Platine, very expensive. In addition, the safety of these piles over one long life is not assured;
- production: by combustion of fossil energies, one falls down then in the problems mentioned previously. But one can then produce it on board vehicles. By Hydrolysis of water, it is then less effective from an energy point of view, and can be made only with large scales. Poses in this case the problems of transport and storage;
- storage: far from dense, hydrogen must be compressed with very important pressures to be transportable in a reasonable volume. In addition to the security issues which it comprises, this compression requires much energy. However the production of this energy, if it is carried out with the traditional means, in particular coal, is likely to emit gases with greenhouse effect and to cancel the environmental advantages brought by the use of hydrogen;
- transport: it would be necessary to set up gigantic infrastructures to produce and transport hydrogen through the territory. It is about an effort comparable with the development of the dies of distribution of the oil, which asked for several tens of years. The cost of the deployment of a complete system of distribution could require from 10 to 15 billion dollars for only the the United States.
New processes bring certain answers to these stakes. The technique of collecting and Séquestration of carbon would make it possible to avoid the gas emission with greenhouse effect during the production of hydrogen, but with high costs: if the manufacture of hydrogen (transport not included/understood) is evaluated with 120 USD the barrel by using natural gas, it should be counted the double if one chooses coal and a technique of collecting/sequestration. Another solution would be to use the nuclear engines specific of generation IV, at very high temperature thanks to the use of helium like coolant, able to produce hydrogen at low cost starting from water. These engines will be available only as from 2030 or 2040.
The use of hydrogen thus constitutes a considerable hope but will not be profitable before several tens of years.
HistoryHydrogen was recognized like a distinct substance in 1766 by Henry Cavendish, in England. Antoine Lavoisier gave him his hydrogen name which comes from the Greek ὕδωρ ( hudôr ), “water” and γεννᾰν ( gennen ), “to generate”.
The Catastrophe of Hindenburg rang the knell of its use in aeronautics.
Sources of hydrogen
OccurrenceHydrogen is the most abundant element of the Universe: 75 % in mass and 90 % of many atoms. This element is in great quantity in the gas star S and planets. Relative with its abundance in the universe, hydrogen is very rare in the Terrestrial atmosphere: approximately 1 ppm in volume.
On Earth, the most common source of hydrogen is the water of which the molecules are made up of two atoms of hydrogen and an atom of Oxygène; but majority of the organic matters, as that which constitutes the living beings, the Pétrole and the Natural gas, are sources of hydrogen. The Methane (C H), which is a product of the decomposition of the organic matters, is used more and more as source of hydrogen.
Hydrogen can be produced in several ways: the action of the vapor on Carbon at high temperature, the Cracking of the Hydrocarbon S by heat, the cracking of the biomass by heat, the action of the Soda or the Potash on the Aluminum, the electrolysis of the Water. Certain micro-organisms (microalgae, cyanobacteries and bacteria) are also able to produce hydrogen, starting from solar energy or of biomass, economic solution which moreover would solve the problem of the organic waste processing.
Hydrogen gross available in the trade is generally manufactured by decomposition of natural gas.
At the 19th century, to produce hydrogen, one heated water, one sent then the steam obtained in a barrel filled with filings and iron chips. The steam H2O attacked the metal creating of iron oxide and releasing the 2 hydrogen molecules. Hydrogen, left then the barrel, one filtered it in another barrel filled with water. Then, direct with the balloon. This device made it possible the army to inflate anywhere and in a few hours an observation balloon.
For more details, to see the article on the Dihydrogène.
Physics and chemistry of hydrogen
Hydrogen combines with the majority of the other elements because it has a average electronegativity (2,2) and can thus form compounds with metal or nonmetal elements. The compounds which it forms with metals are called Hydrure S in which it is in the form of Ion S H − who sometimes exist only in solution. In the compounds with the nonmetal ones, hydrogen forms covalent bonds, because the ion H + , which is anything else only one simple proton, a too strong tendency has to join the electrons. In the acids in aqueous solution, it is formed ions HO + , association of the proton and a water molecule.
Hydrogen combines with oxygen to form water (HO), it is a very energy process of Combustion which is very Explosif in the air. The oxide of Deutérium (C) is commonly called heavy Eau. Hydrogen forms a large variety of made up with carbon; because of their relation with the biological molecules, these compounds are called made up organics and chemistry connects it which relates to them is the Organic chemistry.
FormsUnder normal conditions, the hydrogen gas is a mixture of the type of molecules which differ one from the other by the Spin of their electron and atomic nuclei. These two forms are called ortho- and parahydrogen and forms it para does not exist in a pure state. In the Normal conditions of temperature and pressure, hydrogen is composed with 75 % of the form ortho and with 25 % of the form para. These two forms thus have energy levels slightly different and from the physicochemical properties slightly different. For example, the melting point and the point of boiling of parahydrogen are approximately 0,1 K low than those of the ortho-.
IsotopesThe most common isotope of hydrogen (H), the Protium ( 1 H), simply consists of a proton and thus does not have a Neutron. It is a stable isotope. The Deuterium ( 2 H or D) has a proton and a neutron. It is also a stable isotope which compose between 0,0184 and 0,0082 % of natural hydrogen. The Tritium ( 3 H or T) has a proton and two neutrons; it is a radioactive isotope (unstable), which changes into 3 He by emission of an electron (Radioactivity β − ). 2 H and 3 H can take part in reactions of nuclear Fusion.
Hydrogen is the only element whose isotopes received a specific name. indeed, the difference in mass between the isotopes is significant (the simple one with the double or triple). Consequently, and contrary to what is known as for the isotopes in general in the introductory courses of chemistry, this can influence the chemical properties of deuterium or tritium compared to protium (isotopic effect).
Danger, risk and precautions
The dihydrogene is a flammable gas classified as “extremely ” (the history of its use in the balloons Dirigeable S is strewn with serious accidents which justified its replacement by the Hélium much more expensive and less light). It is characterized by a very broad field of inflammability (of 4 with 75 % of volume in the air), causing a deflagration starting from a contribution of very weak energy of ignition (a spark is enough if it brings an energy of 0,02 millijoule (mJ) whereas 0,29  is needed; mJ to start a Explosion Methane).
The heavy Eau (C) is toxic for many species. Indeed because of the great difference in mass between the isotopes the kinetics of the reactions in aqueous solution “heavy” is slowed down considerably (isotopic effect); but the quantity necessary to kill an human being is substantial. The hydrogen mixed with oxygen in the stoechiometric proportions is a powerful explosive. The dihydrogene in the air is a clashing mixture when the voluminal report/ratio H/air lies between 13 and 65 %.
Industry stores dihydrogene outside the buildings, which will not be possible for an embarked use (vehicles, ships). The Norme S of safety are reinforced to answer the risks posed by the passage in the tunnels and the parking in the garages or underground car parks.
The world regulation on the vehicles is worked out under the aegis of UNO starting from the proposals of the industrialists, but concerning dihydrogene, the Japanese constructors, American and Europeans do not agree. The European commission could decide on a provisional Community legislation. In France, the Ineris and the ECA work with the International organization of standardization (ISO) in a technical committee named TC 197 on the dihydrogene risk. An European project Hysafe treats also question, where Ineris criticized the draft Regulation by suggesting a more global and systemic solution and not per component for the homologation of the hybrid vehicles.
The hydrogen atom being the simplest atom, it is the first which was studied within the framework of the Quantum physics.
See also: Atom of hydrogen
The chemistry of hydrogen
The connections which the hydrogen atom can establish can be of three kinds:
- the loss of an electron. Hydrogen becomes H then + (a Proton only). Its ray is then very small: approximately 1,5×10 −13 cm against 0,5×10 −8 cm for the atom. The all alone proton does not exist free but it is always in the electronic cloud of a molecule (such HO); becoming the ion hydronium (acid): HOH + .
- acquisition of an electron. Hydrogen becomes H then − (a Hydride). The ion itself does not exist as such as in salts of hydrides;
- formation of a Covalent bond. Hydrogen thus makes a covalent bond a pooling of a pair of electrons with other atoms as in HO or CH.
The hydrogen bond
The Hydrogen bond is an electrostatic interaction between hydrogen chemically dependant on an electronegative atom has and another electronegative atom B (has and B being typically O, NR or F in organic chemistry). For example: NH-O=C, or in water HO-H-O-H.
This connection plays a big role in organic chemistry but also in inorganic chemistry, between alcohols and metals Alkoxide S. We distinguish three types in general:
weak with enthali between 10 - 50 kJ·mol −1 ;
- strong with enthali between 50 - 100 kJ·mol −1 ;
- very strong with enthalpy > 100 kJ·mol −1 .
An example of very strong connection is FH-F −1 in KHF with approximately 212 kJ·mol −1 . One can think that in this case it is to better write F-H-F. The total distance between F-H-F is of 2,49 Å only and it is formed an angle of 120° between the various molecules.
There exist hydrogen bonds in multiple centers. In general they are systems in three centers and seldom with four. Either a H is related to two other molecules or two hydrogen are related to another molecule.
the Revolution of hydrogen. Towards an clean energy and powerful? , Stephen Butcher, foreword of Thierry Alleau, Paris, ED. the Cat-like one, 2006,160 pages, ISBN 2-86645-616-5.
- Dihydrogène (H2)
- Hydrogenation in organic chemistry
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