Gadson,+Chris


 * 1.Atomic number: **2 


 * 2.Atomic mass: **4.00260 g.mol -1


 * 3.Electronegativity according to Pauling: unknown **
 * 4.Density: ** 0.178*10 -3 g.cm -3 at 20 °C


 * 5.Melting point: ** - 272.2 (26 atm) °C


 * 6.Boiling point: ** - 268.9 °C


 * 7.Ionic radius: ** unknown


 * <span style="color: #002060; font-family: 'Verdana','sans-serif'; font-size: 18pt; mso-bidi-font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman';">8.Isotopes: **<span style="color: #002060; font-family: 'Verdana','sans-serif'; font-size: 18pt; mso-bidi-font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman';"> 2

10.Energy of first ionisation: **<span style="color: #002060; font-family: 'Verdana','sans-serif'; font-size: 18pt; mso-bidi-font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman';"> 2372 kJ.mol -1
 * <span style="color: #002060; font-family: 'Verdana','sans-serif'; font-size: 18pt; mso-bidi-font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman';">9.Electronic shell: **<span style="color: #002060; font-family: 'Verdana','sans-serif'; font-size: 18pt; mso-bidi-font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman';"> 1s 2
 * <span style="color: #002060; font-family: 'Verdana','sans-serif'; font-size: 18pt; mso-bidi-font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman';">

Scientific discoveries
The first evidence of helium was observed on August 18, 1868 as a bright yellow line with a [|wavelength] of 587.49 nanometers in the [|spectrum] of the [|chromosphere] of the [|Sun]. The line was detected by French astronomer [|Pierre Janssen] during a total [|solar eclipse] in [|Guntur], [|India]. [|[2]][|[3]] This line was initially assumed to be [|sodium]. On October 20 of the same year, English astronomer [|Norman Lockyer] observed a yellow line in the solar spectrum, which he named the D3 [|Fraunhofer line] because it was near the known D1 and D2 lines of sodium. [|[4]] He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and English chemist [|Edward Frankland] named the element with the Greek word for the Sun, <span style="color: #002060; font-family: 'Tahoma','sans-serif'; font-size: 20pt; mso-ansi-language: EN;">ἥ <span style="color: #002060; font-family: Times New Roman; font-size: 20pt; mso-ansi-language: EN; msoansilanguage: EN;">λιος (// [|helios] //)." [|[5]][|[6]][|[7]]  <span style="color: #002060; font-size: 20pt; line-height: 115%; mso-no-proof: yes; text-decoration: none; text-underline: none;">  <span style="color: #002060; font-size: 20pt; line-height: 115%; mso-no-proof: yes; text-decoration: none; text-underline: none;">  Spectral lines of helium    In 1882, Italian physicist [|Luigi Palmieri] detected helium on [|Earth], for the first time, through its D3 spectral line, when he analyzed the [|lava] of [|Mount Vesuvius]. [|[8]] On March 26, 1895 British chemist [|Sir William Ramsay] isolated helium on Earth by treating the mineral [|cleveite] (a variety of [|uraninite] with at least 10% [|rare earth elements] ) with mineral [|acids]. Ramsay was looking for [|argon] but, after separating [|nitrogen] and [|oxygen] from the gas liberated by [|sulfuric acid], he noticed a bright yellow line that matched the D3 line observed in the spectrum of the Sun. [|[4]][|[9]][|[10]][|[11]] These samples were identified as helium by Lockyer and British physicist [|William Crookes]. It was independently isolated from cleveite in the same year by chemists [|Per Teodor Cleve] and [|Abraham Langlet] in [|Uppsala, Sweden], who collected enough of the gas to accurately determine its [|atomic weight]. [|[3]][|[12]][|[13]] Helium was also isolated by the American geochemist [|William Francis Hillebrand] prior to Ramsay's discovery when he noticed unusual spectral lines while testing a sample of the mineral uraninite. Hillebrand, however, attributed the lines to nitrogen. His letter of congratulations to Ramsay offers an interesting case of discovery and near-discovery in science. [|[14]] In 1907, [|Ernest Rutherford] and Thomas Royds demonstrated that [|alpha particles] are helium [|nuclei] by allowing the particles to penetrate the thin glass wall of an evacuated tube, then creating a discharge in the tube to study the spectra of the new gas inside. In 1908, helium was first liquefied by Dutch physicist [|Heike Kamerlingh Onnes] by cooling the gas to less than one [|kelvin]. [|[15]] He tried to solidify it by further reducing the temperature but failed because helium does not have a [|triple point] temperature at which the solid, liquid, and gas phases are at equilibrium. Onnes' student [|Willem Hendrik Keesom] was eventually able to solidify 1 cm3 of helium in 1926. [|[16]] In 1938, Russian physicist [|Pyotr Leonidovich Kapitsa] discovered that [|helium-4] has almost no [|viscosity] at temperatures near [|absolute zero], a phenomenon now called [|superfluidity]. [|[17]] This phenomenon is related to [|Bose-Einstein condensation]. In 1972, the same phenomenon was observed in [|helium-3], but at temperatures much closer to absolute zero, by American physicists [|Douglas D. Osheroff] , [|David M. Lee] , and [|Robert C. Richardson]. The phenomenon in helium-3 is thought to be related to pairing of helium-3 [|fermions] to make [|bosons], in analogy to [|Cooper pairs] of electrons producing [|superconductivity]. [|[18]]

<span style="color: #002060; font-family: 'Arial','sans-serif'; font-size: 18pt; mso-fareast-font-family: 'Times New Roman';"> Uses of helium <span style="font-family: 'Arial','sans-serif'; font-size: 18pt; mso-fareast-font-family: 'Times New Roman';"> <span style="font-family: 'Arial','sans-serif'; font-size: 18pt; mso-fareast-font-family: 'Times New Roman';">
 * <span style="font-family: 'Arial','sans-serif'; font-size: 18pt; mso-fareast-font-family: 'Times New Roman';">as an inert gas shield for arc welding;
 * <span style="font-family: 'Arial','sans-serif'; font-size: 18pt; mso-fareast-font-family: 'Times New Roman';">a protective gas in growing silicon and germanium crystals and producing titatium and zirconium;
 * <span style="font-family: 'Arial','sans-serif'; font-size: 18pt; mso-fareast-font-family: 'Times New Roman';">as a cooling medium for nuclear reactors, and
 * <span style="font-family: 'Arial','sans-serif'; font-size: 18pt; mso-fareast-font-family: 'Times New Roman';">as a gas for supersonic wind tunnels.