Gruppo: 18 or VIII A
Peso atomico: 4.002602
Numero CAS: 7440-59-7
Non ci sono isotopi stabili
Descrizione • Usi / Funzione
Evidence of the existence of helium was first obtained by Janssen during the solar eclipseof 1868 when he detected a new line in the solar spectrum; Lockyer and Frankland suggested the name helium for the new element; in 1895, Ramsaydiscovered helium in the uranium mineral clevite, and it was independently discovered in cleveite by the Swedish chemists Cleve and Langlet aboutthe same time. Rutherford and Royds in 1907 demonstrated that a particles are helium nuclei. Except for hydrogen, helium is the most abundant elementfound throughout the universe. Helium is extracted from natural gas; all natural gas contains at least trace quantities of helium. It has been detectedspectroscopically in great abundance, especially in the hotter stars, and it is an important component in both the proton-proton reaction and the carboncycle, which account for the energy of the sun and stars. The fusion of hydrogen into helium provides the energy of the hydrogen bomb. The heliumcontent of the atmosphere is about 1 part in 200,000. While it is present in various radioactive minerals as a decay product, the bulk of the Free World’ssupply is obtained from wells in Texas, Oklahoma, and Kansas. The only known helium extraction plants, outside the United States, in 1996 were inEastern Europe (Poland), the Russia, China, and India. The cost of helium fell from $2500/ft3 in 1915 to 1.5¢/ft3 in 1940. Commercial helium in 1996was priced at about $70/300 cu. ft. (8.5 cu. meters). Helium has the lowest melting point of any element and has found wide use in cryogenic research,as its boiling point is close to absolute zero. Its use in the study of superconductivity is vital. Using liquid helium, Kurti and co-workers, and others,have succeeded in obtaining temperatures of a few microkelvins by the adiabatic demagnetization of copper nuclei, starting from about 0.01 K. Sevenisotopes of helium are known. Liquid helium (He4) exists in two forms: He4I and He4II, with a sharp transition point at 2.174 K (3.83 cm Hg). He4I(above this temperature) is a normal liquid, but He4II (below it) is unlike any other known substance. It expands on cooling; its conductivity for heatis enormous; and neither its heat conduction nor viscosity obeys normal rules. It has other peculiar properties. Helium is the only liquid that cannotbe solidified by lowering the temperature. It remains liquid down to absolute zero at ordinary pressures, but it can readily be solidified by increasingthe pressure. Solid 3He and 4He are unusual in that both can readily be changed in volume by more than 30% by application of pressure. The specificheat of helium gas is unusually high. The density of helium vapor at the normal boiling point is also very high, with the vapor expanding greatly whenheated to room temperature. Containers filled with helium gas at 5 to 10 K should be treated as though they contained liquid helium due to the largeincrease in pressure resulting from warming the gas to room temperature. While helium normally has a 0 valence, it seems to have a weak tendencyto combine with certain other elements. Means of preparing helium diflouride have been studied, and species such as HeNe and the molecular ionsHe+ and He++ have been investigated. Helium is widely used as an inert gas shield for arc welding; as a protective gas in growing silicon and germaniumcrystals, and in titanium and zirconium production; as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels. A mixture ofhelium and oxygen is used as an artificial atmosphere for divers and others working under pressure. Different ratios of He/O2 are used for differentdepths at which the diver is operating. Helium is extensively used for filling balloons as it is a much safer gas than hydrogen. One of the recent largestuses for helium has been for pressuring liquid fuel rockets. A Saturn booster such as used on the Apollo lunar missions required about 13 million ft3ofhelium for a firing, plus more for checkouts. Liquid helium’s use in magnetic resonance imaging (MRI) continues to increase as the medical professionaccepts and develops new uses for the equipment. This equipment is providing accurate diagnoses of problems where exploratory surgery haspreviously been required to determine problems. Another medical application that is being developed uses MRI to determine by blood analysis whethera patient has any form of cancer. Lifting gas applications are increasing. Various companies in addition to Goodyear, are now using “blimps” foradvertising. The Navy and the Air Force are investigating the use of airships to provide early warning systems to detect low-flying cruise missiles.The Drug Enforcement Agency has used radar-equipped blimps to detect drug smugglers along the southern border of the U.S. In addition, NASAis currently using helium-filled balloons to sample the atmosphere in Antarctica to determine what is depleting the ozone layer that protects Earth fromharmful U.V. radiation. Research on and development of materials which become superconductive at temperatures well above the boiling point ofhelium could have a major impact on the demand for helium. Less costly refrigerants having boiling points considerably higher could replace the presentneed to cool such superconductive materials to the boiling point of helium. 1
• "Helium gas is used instead of hydrogen for filling balloons and dirigibles because it is non-flammable and has a lifting power only about 8 percent less than hydrogen. Helium is a component of the artificial atmosphere supplied to men engaged in deep diving and caisson operations because helium is much less soluble in blood than nitrogen. (The time required to reduce the pressure to atmospheric without causing the bends is greatly reduced by replacing the nitrogen of air with helium.) Helium is also used as a diluent for oxygen in asthma therapy when the air passages are constricted. Liquid helium is used as a coolant and heat transfer medium in cryogenic studies in the neighborhood of 0-5 K. Helium gas is used as a heat transfer agent in gas-cooled atomic reactors because it is chemically inert and does not become radioactive. Both helium and argon are used in large amounts in noble-gas-shielded arc-welding processes. The noble gas protects the hot welded metal from oxidation by air." 2
• "filling of observation balloons and other lighter-than-air craft...He/O2, for deep-sea breathing...diluent for gaseous anesthetics...He/O2 mixtures for respiratory patients...heat transfer medium for nuclear reactors" 3
Punto di fusione:4*
Punto di ebollizione:4* -268.93 °C = 4.21999999999997 K = -452.074 °F
Punto critico:4 -267.96 °C = 5.19 K = -450.328 °F 4
Densità:5 0.164 g/L
* - at 1 atm
configurazione elettronica: 1s2
Più alto livello di energia Occupato: 1
Elettroni di valenza: 2
n = 1
ℓ = 0
mℓ = 0
ms = -½
Affinità elettronica:6 not stable eV
ossidazione Uniti: 0
|potenziale di ionizzazione||eV 7||kJ/mol|
|potenziale di ionizzazione||eV 7||kJ/mol|
|potenziale di ionizzazione||eV 7||kJ/mol|
Calore specifico: 5.193 J/g°C 8 = 20.786 J/mol°C = 1.241 cal/g°C = 4.968 cal/mol°C
Calore di fusione:
Calore di vaporizzazione: 0.0845 kJ/mol 10 = 21.1 J/g
|Stato della materia||Entalpia di formazione (ΔHf°)11||entropia (S°)11||Energia libera di Gibbs (ΔGf°)11|
|nuclide||Massa 12||Metà vita 12||spin nucleare 12||Energia di legame|
|10He||10.05240(8)||2.7(18)E-21 s [0.17(11) MeV]||0+||30.71 MeV|
|5He||5.01222(5)||700(30)E-24 s [0.60(2) MeV]||3/2-||27.43 MeV|
|6He||6.0188891(8)||806.7(15) ms||0+||29.35 MeV|
|7He||7.028021(18)||2.9(5)E-21 s [159(28) keV]||(3/2)-||28.85 MeV|
|8He||8.033922(7)||119.0(15) ms||0+||31.43 MeV|
|9He||9.04395(3)||7(4)E-21 s [100(60) keV]||1/2(-#)||30.18 MeV|
|I valori assegnati # non sono puramente derivati da dati sperimentali, ma almeno parzialmente da tendenze sistematiche. Gira con argomenti di assegnazione deboli sono racchiusi tra parentesi. 12|
Terra - composti di origine: uncombined 13
Terra - L'acqua di mare: 0.000007 mg/L 14
Terra - Crosta: 0.008 mg/kg = 0.0000008% 14
Terra - Totale: 111E-8 cm^3/g 15
Pianeta Mercurio) - Totale: 15
Venere - Totale: 11000E-8 cm^3/g 15
Universo - Totale: 24.0% 16
condriti - Totale: 0.11 (relative to 106 atoms of Si) 17
Informazioni sulla sicurezza
Scheda di sicurezza - ACI Alloys, Inc.
Per maggiori informazioni
Chemical & Engineering News
HyperPhysics from Georgia State University's Department of Physics and Astronomy
Los Alamos National Laboratory
Physics Department of the University of Coimbra
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(2) Cowen, Ron. Relic Radiation Refines Age of Cosmos. Science News, February 27, 2010, pp 7.
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