Heliumo

He ↓ Ne hidrogeno ← heliumo → litio • 1s2 He 2 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ↓Perioda tabelo de elementoj↓
kemia elemento • atmophile element
s-bloko • nemetalo • nobla gaso
Ĝeneralaj informoj
Nomo (latine), simbolo, numero	heliumo (helium), He, 2
CAS-numero	7440-59-7
Loko en perioda tabelo	18-a grupo, 1-a periodo, bloko s
Karakteriza grupo	Raraj gasoj
abundeco en terkrusto	4 · 10–7 %
Nombro de naturaj izotopoj	2
Aspekto	senkolora gaso
Atomaj ecoj
Relativa atompezo	4,002602(2)[1] amu
Kovalenta radiuso	28 pm
Radiuso de van der Waals	140 pm
Elektrona konfiguracio	1s2
Elektronoj en ĉiu energia ŝelo	2
Oksidiĝa nombro	0
Fizikaj ecoj
Materia stato	gasa (He)
Kristala strukturo	heksagona
Denseco	(273,15 K) 1,785 · 10–4 g/cm3 (−268,93 K) 1,25 · 10–1 g/cm3 (−272,20 K) 1,45 · 10–1 g/cm3
Magneta konduto	diamagneta (${\displaystyle \chi _{m}}$ = −1,1 · 10−9)
Degelpunkto	(2,5 MPa) −272,20 °C (0,95 K)
Bolpunkto	−268,928 °C (4.222 K)
Molvolumeno	(solida) 22,42 · 10−6 m3/mol
Degeliga varmo	0,02 kJ/mol
Boliga varmo	0,0840 kJ/mol
Rapido de sono	(273,15 K) 972 m/s
Specifa varmokapacito	5193 J/(kg · K)
Termika konduktivo	0,1513 W/(m · K)
Diversaj
Elektronegativeco	4.5 (Pauling-skalo)
Joniga energio	1-a: 2372,3 kJ/mol 2-a: 5250,5 kJ/mol
Izotopoj
Izotopo Naturapero t1/2 radioaktiveco de disfalo Energio de disfalo MeV Produkto de radioaktiva disfalo 3He 0,000137% estas stabila kun 1 neŭtrono 4He 99,999863% estas stabila kun 2 neŭtronoj 5He artefarita 7,618 · 10−22 s n 0,60 4He 6He artefarita 806,7 ms β− 3,508 6Li
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Heliumo aŭ helio (He) estas kemia elemento de la perioda tabelo kun la simbolo He kaj atomnumero 2. Ĝi estas senkolora, senodora, sengusta, inerta. La bolpunkto kaj frostopunkto estas tre malaltaj inter la elementoj, kaj ĝi ekzistas kiel gaso krom en ekstremaj kondiĉoj.

Heliumo estas la dua plej abunda elemento en la universo (23 centonoj de la videbla universo).

Estas multo da heliumo en la suno. Fakte, la fuzio de hidrogeno al heliumo produktas la sunan energion. La angla astronomo Sir Joseph Lockyer vidis heliumon en la suno dum eklipso en 1868 kaj nomis la elementon "heliumo" (de la helena helios, "suno").

La Nomo Heliuma devenas de la Helena dio de Suno, kiu havas la nomon Helios. Heliumon rimarkis unue Georges Rayet,^[2] C. T. Haig,^[3] Norman R. Pogson,^[4] kaj John Herschel dum suna eklipso de 1868.^[5] Ili rimarkis linion spektran flavan en la sunlumo. La malkovron konfirmis Jules Janssen, kiu estis astronomo francia.^[6]

1. ↑  (angle): Atomic weights of the elements 2013 (IUPAC Technical Report) (PDF), p. 8
2. ↑ Rayet, G. (1868) "Analyse spectral des protubérances observées, pendant l'éclipse totale de Soleil visible le 18 août 1868, à la presqu'île de Malacca"^{[permanent dead link]}(Spectral analysis of the protuberances observed during the total solar eclipse, seen on 18 August 1868, from the Malacca peninsula), Comptes rendus … , 67 : 757–759. From p. 758: " … je vis immédiatement une série de neuf lignes brillantes qui … me semblent devoir être assimilées aux lignes principales du spectre solaire, B, D, E, b, une ligne inconnue, F, et deux lignes du groupe G." ( … I saw immediately a series of nine bright lines that … seemed to me should be classed as the principal lines of the solar spectrum, B, D, E, b, an unknown line, F, and two lines of the group G.)
3. ↑ Captain C. T. Haig (1868) "Account of spectroscopic observations of the eclipse of the sun, August 18th, 1868," Proceedings of the Royal Society of London, 17 : 74–80. From p. 74: "I may state at once that I observed the spectra of two red flames close to each other, and in their spectra two broad bright bands quite sharply defined, one rose-madder and the other light golden."
4. ↑ Pogson filed his observations of the 1868 eclipse with the local Indian government, but his report wasn't published. (Biman B. Nath, The Story of Helium and the Birth of Astrophysics (New York, New York: Springer, 2013), p. 8.) Nevertheless, Lockyer quoted from his report. From p. 320 of Lockyer, J. Norman (1896) "The story of helium. Prologue," Nature, 53 : 319–322 : "Pogson, in referring to the eclipse of 1868, said that the yellow line was "at D, or near D." "
5. ↑ Lieutenant John Herschel (1868) "Account of the solar eclipse of 1868, as seen at Jamkandi in the Bombay Presidency," Proceedings of the Royal Society of London, 17 : 104–120. From p. 113: As the moment of the total solar eclipse approached, " … I recorded an increasing brilliancy in the spectrum in the neighborhood of D, so great in fact as to prevent any measurement of that line till an opportune cloud moderated the light. I am not prepared to offer any explanation of this." From p. 117: "I also consider that there can be no question that the ORANGE LINE was identical with D, so far as the capacity of the instrument to establish any such identity is concerned."
6. ↑ In his initial report to the French Academy of Sciences about the 1868 eclipse, Janssen made no mention of a yellow line in the solar spectrum. See: Janssen (1868) "Indication de quelques-uns des résultats obtenus à Cocanada, pendant l'éclipse du mois d'août dernier, et à la suite de cette éclipse" (Information on some of the results obtained at Cocanada, during the eclipse of the month of last August, and following that eclipse), Comptes rendus … , 67 : 838–839. Wheeler M. Sears, Helium: The Disappearing Element (Heidelberg, Germany: Springer, 2015), p. 44. Françoise Launay with Storm Dunlop, trans., The Astronomer Jules Janssen: A Globetrotter of Celestial Physics (Heidelberg, Germany: Springer, 2012), p. 45. However, subsequently, in an unpublished letter of 19 December 1868 to Charles Sainte-Claire Deville, Janssen asked Deville to inform the French Academy of Sciences that : "Several observers have claimed the bright D line as forming part of the spectrum of the prominences on 18 August. The bright yellow line did indeed lie very close to D, but the light was more refrangible [i.e., of shorter wavelength] than those of the D lines. My subsequent studies of the Sun have shown the accuracy of what I state here." (See: (Launay, 2012), p. 45.)