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Chemical, physical and material properties and data of the chemical element Helium.



Helium is the chemical element with the symbol He and atomic number 2. It is a colourless, odorless and tasteless noble gas found in the second main group and first period of the periodic table of elements.

Helium is the second most abundant element in the Universe, accounting for about 23% of the mass of the observable Universe. However, it is very rare on Earth and is mainly extracted from natural gas (air) deposits. It is very light and has a lower density than air, which is why it is often used in balloons. Helium is also a very stable element and only reacts with other elements under very specific conditions.

Helium was discovered in 1868 by French astronomer Pierre Janssen while observing the solar eclipse. Janssen noticed that the sun's light was repeatedly absorbed by a specific element, which he identified as helium. A few years later, in 1895, the element was also discovered on Earth by British chemist Sir William Ramsay while studying the mineral krynite.


General Information about Helium

Regular nameHeliumChemical symbolHeOther namesElement 2Systematic nameHistorical namesName meaning, originGreek helios = sun - due to the bright, yellow spectral line in sunlight that comes from heliumDiscovery (year)(1868) - Pierre Janssen, Norman Lockyer. First isolated in 1895 by William Ramsay, Per Teodor Cleve, Abraham LangletOccurenceSecond most abundant element in the universe and second most abundant element in Earth's atmospherePosition in the PSEGroup 18, period 1, s-block, main group IIGroup membershipNoble gases


Atomar Properties of Helium

Atomic number Z2 = number of protonsStandard Atomic Weight4.002602 (2)


Electron configuration of Helium


Abbreviated form: 1s2.


Ionization Energies of Helium

The following table lists the ionization energies IE (ionization potentials); the IE is the energy required in electron volts (eV) per atom to separate a given electron from an Helium atom.



Isotopic Data of Helium

An overview of the nuclides as well as the isotopic data and properties are listed on the following page: Helium isotopes.


Chemistry of Helium


Oxidation states0Electronegativity
4.160 (Allen)
12.0568 eV (Gosh Gupta)


Material and Physical Properties

Melting point- 272.20 °CEnthalpy of fusion (molar)0.0138 kJ mol-1Boiling point- 268.923 °CEnthalpy of vaporization0.082 kJ mol-1Density0.1786 g L -1 (0°C; 101.325 kPa)


External Data, Identifiers

CAS registry number7440-59-7InChI =1S/HeInChIKeySWQJXJOGLNCZEY-UHFFFAOYSA-NPubChem ID23987


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Last update: 2022-12-21

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