Helium is the lightest noble gas with two electrons filling the 1s state to close the first shell. It is the second most abundant element in the universe, following hydrogen. The hydrogen-helium abundance ratio is an important clue to the cosmological process.
Further data for naturally occuring isotopes of helium are listed above. This table gives information about some radiosotopes of helium, their masses, their half-lives, their modes of decay, their nuclear spins, and their nuclear magnetic moments. Isotope Mass / Da Half-life Mode of decay Nuclear spin Nuclear magnetic moment; 6 He: 6.018886: 0.807 s: β-to 6 Li: 3 / 2. Helium, the lightest of the noble gases, had actually been detected and helium is the only element in the periodic table that was discovered by an astronomer. Helium is the element which you can find on the upper right side of the periodic table with atomic number 2. Atomic Mass of Helium Atomic mass of Helium is 4.0026 u. Helium-4 atom is the stable isotope of helium with relative atomic mass 4.002603. The most abundant (99.99 atom percent) isotope of naturally occurring helium.It contains an alpha-particle. Exact Mass: 4.002603 g/mol: Computed by PubChem 2.1 (PubChem release 2019.06.18) Monoisotopic Mass: 4.002603 g/mol: Computed by PubChem 2.1 (PubChem release 2019.06.18) Topological Polar Surface Area: 0 Ų: Computed by Cactvs 3.4.6.11 (PubChem release 2019.06.18) Heavy Atom Count: 1: Computed by PubChem: Formal Charge: 0: Computed by PubChem: Complexity: 0.
On the earth, helium is not abundant, being found only in very small quantities in the earth's atmosphere. It was in fact discovered in the sun by the helium spectrum in 1868, long before it was discovered on the earth.
Helium occurs as a gas entrapped in some uranium minerals, from which it can be liberated by heating. This helium presumably has its origin from alpha decay in the radioactive material. Helium is also present in natural gas from some wells, especially in Texas and Canada, and this is its principal source.
Helium is used for filling balloons and dirigibles. It is mixed with oxygen (heliox) for breathing by deep ocean divers to avoid the 'bends' from the nitrogen content of the breathed air.
Liquid helium provides the most practical way to achieve temperatures below 20K for research purposes, and it provides the coolant for achieving superconductivity with the Type I superconductors.
For high vacuum research, helium provides a sensitive way to locate leaks in the vacuum system. A helium mass spectrometer is attached to the vacuum system and then a small jet of helium is released outside the vacuum at locations where leaks are suspected. The detection of helium by the mass spectrometer shows that some is getting into the system, and that the release must be close to the leak.
| Atomic data | Nuclear data |
| Electron energy level diagram |
| Isotope | Atomic mass (Da) | Isotopic abundance (amount fraction) |
|---|---|---|
| 3He | 3.016 029 322(2) | 0.000 002(2) |
| 4He | 4.002 603 2545(4) | 0.999 998(2) |
In contrast to the other noble gases, which are separated for commercial use almost entirely fromair, a large amount of commercial He is derived from natural gas deposits containing relatively high concentrationsof radiogenic 4He. In its 1961 report, the Commission recommended Ar(He) = 4.0026 based onthe atomic mass of 4He to four decimal places. The abundance of 3He in airof 0.000 137 % as determined by Nier had a negligible effect on the atomic weight of helium. This isotopeis present in natural sources of helium with a smaller abundance than that of any other stable isotope relativeto its elemental composition. In 1969 the Commission recommended Ar(He) = 4.002 60(1), which was identical to the atomic mass of 4He to six significant figures.A subsequent determination of the isotopic composition of atmospheric helium have confirmed this value which has been last revised in 1983.
Helium Atomic Mass In Kg
The indicated interval for the standard atomic weight of He has a lower limit of 4.002 600, correspondingto an abundance of x(3He) = 3.3×10-6. This interval includes some natural 3He-enrichedsources, but it does not include all helium from volcanic rocks or associated geothermal springs and gases,some of which have 3He abundances more than ten times that of atmospheric helium, hence the annotation'g'. Those types of 3He-enriched sources are considered to represent emissions of primordial heliumfrom incompletely degassed regions deep within the earth.
Helium, a noble gas, is chemically the most unreactive element with the lowest boiling point (4.2 K). Apart from its presence in gaseous or fluid inclusions and interstitial positions in crystals, andin voids in clathrate compounds, He occurs naturally only as a monoatomic gas. Helium is too light tobe held in the atmosphere by Earth's gravitation over periods comparable with the age of the earth; thus,4He in the atmosphere has been derived almost entirely from degassing of the solid earth, where it isproduced by alpha decay of heavy radioisotopes. The minor isotope 3He is believed to be largely primordial,with minor amounts derived from beta decay of 3H, which is produced by the reaction 6Li(n,α)3H in the earth, by cosmic-ray reactions in the atmosphere, or by nuclear explosions and industry.Accumulations of 3He produced by radioactive decay of anthropogenic 3H provide a useful tool for determiningages of groundwaters and surface waters, including the ocean. The physical properties of 3Hein gas, liquid, and solid phases and of 3He and 4He mixtures have been the subjects of many experimentalstudies that have contributed decisively to our understanding of quantum physics and chemistry
© IUPAC 2003
CIAAW
Atomic Weight Of Helium
Helium
Ar(He) = 4.002 602(2) since 1983
The name derives from the Greek helios for 'sun'. The element was discovered by spectroscopy duringa solar eclipse in the sun's chromosphere by the French astronomer Pierre-Jules-Cesar Janssen in1868. It was independently discovered and named helium by the English astronomer Joseph NormanLockyer.
Helium was thought to be only a solar constituent until it was later found to be identical to the heliumin the uranium ore cleveite by the Scottish chemist William Ramsay in 1895. The Swedish chemists Per Theodore Cleve andNils Abraham Langet independently found helium in cleveite at about the same time.