Helium is the chemical element with atomic number 2, symbol He

Helium is the chemical element with atomic number 2, symbol He

Helium is the chemical element with atomic number 2, symbol He

Helium it is a noble gas (or rare gas), practically inert, the first of the noble gas family in the periodic table of the elements. Its boiling point is the lowest among known bodies, and it only exists in solid form when subjected to a pressure greater than 25 atmospheres.

Appearance: colorless gas, exhibiting a gray, cloudy glow (or reddish-orange if an especially high voltage is used) when placed in an electric field.

It is the second lightest element (only hydrogen is lighter), this gas is a colourless, odourless, and tasteless gas that becomes liquid at −268.9 °C (−452 °F). The boiling and freezing points of helium are lower than those of any other known substance. Helium is the only element that cannot be solidified by sufficient cooling at normal atmospheric pressure; it is necessary to apply pressure of 25 atmospheres at a temperature of 1 K (−272 °C, or −458 °F) to convert it to its solid form.

Is it dangerous to breathe helium?

Helium inhalation: the risks

It is an inert or inactive gas, harmless to health. But the one found, for example in inflatable balloons at the fair, is often mixed with other gases which can be dangerous. Excessive inhalation of even pure helium can also pose risks. Inhalation of helium is not harmful to health. However, excessive consumption should be avoided. Many people breathe in this gas to modify their voice. This is possible as part of a show or to amuse small children. Voice imitators also need to change their vocal timbre. You can breathe helium to make your voice high or low. The modification process is very simple. The low density of the gas gives it this ability.

Health effects of helium

Effects of exposure: The substance can be absorbed into the body by inhalation. Inhalation: vertigo, headache, suffocation. Skin: if in contact with liquid: frostbite. Eyes: if in contact with liquid: frostbite. Inhalation hazard: this gas can cause suffocation by lowering the oxygen content of the air in confined areas. Check the oxygen content before entering the area.

Use of helium

Helium is administered in mixtures containing a minimum of 20% dioxygen to patients with upper or lower airway obstruction. The low viscosity of helium thus reduces the work of breathing.
Liquid helium is used to cool superconducting magnets (MRI, the LHC {Large Hadron Collider}).
Low temperature of this gas is used in cryogenics.
It is used as a transfer fluid in certain gas-cooled nuclear reactors.
It is used to pre-cool liquid hydrogen in space vehicles.
It serves as a protective atmosphere during the manufacture of electronic circuits, optical fibers and the production of certain metals.
Used to check the tightness of equipment (tanks) and food packaging.
Allows rock and mineral dating (helium dating).
Is used in diving as a mixture (trimix, heliair, heliox) to reach great depths by limiting the effects of “nitrogen narcosis” (deep intoxication).
Used in laser barcode readers (helium / neon mixture).
Meteorologists use it to explore the atmosphere (weather balloons).
The other major market for helium is electronics, where it is used to create clean atmospheres in the manufacturing process, as well as for cooling in fiber optic production.
It is also used in the space sector, to cool satellite launchers, and in the automobile industry for the production of airbags.

How and where is it produced?

Helium cannot be produced artificially at present. However, it is contained in natural gas fields, from where it is extracted by cryogenic process. Today “80 to 90%” of the world production of helium comes from this technique.

The United States today produces about 60% of the world’s helium. Having grasped the high strategic interest of this gas very early on, the country has a huge federal helium reserve near Amarillo (Texas), currently corresponding to 25-30% of global demand.

Qatar is the second largest producer of helium, providing around a quarter of global production, while Algeria, Russia and Australia share around 10% of the market.

As for the global helium suppliers, the top three is made up of the German Linde, the French Air Liquide and the American Praxair.

Helium in the periodic table

Atomic number (Z)2
Groupgroup 18 (noble gases)
Periodperiod 1
Block  s-block
Electron configuration1s2
Electrons per shell2

Physical properties

Physical properties
Phase at STPgas
Melting point0.95 K ​(−272.20 °C, ​−457.96 °F) (at 2.5 MPa)
Boiling point4.222 K ​(−268.928 °C, ​−452.070 °F)
Density (at STP)0.1786 g/L
when liquid (at m.p.)0.145 g/cm3
when liquid (at b.p.)0.125 g/cm3
Triple point2.177 K, ​5.043 kPa
Critical point5.1953 K, 0.22746 MPa
Heat of fusion0.0138 kJ/mol
Heat of vaporization0.0829 kJ/mol
Molar heat capacity20.78 J/(mol·K)

Vapor pressure (defined by ITS-90)

P (Pa)1101001 k10 k100 k
at T (K)1.231.672.484.21

Atomic properties

Atomic properties
Oxidation states0
ElectronegativityPauling scale: no data
Ionization energies
  • 1st: 2372.3 kJ/mol
  • 2nd: 5250.5 kJ/mol
Covalent radius28 pm
Van der Waals radius140 pm

Other properties

Other properties
Natural occurrenceprimordial
Crystal structure​hexagonal close-packed (hcp)
Speed of sound972 m/s
Thermal conductivity0.1513 W/(m·K)
Magnetic orderingdiamagnetic[3]
Magnetic susceptibility−1.88·10−6 cm3/mol (298 K)
CAS Number7440-59-7


Namingafter Helios, Greek god of the Sun
DiscoveryPierre Janssen, Norman Lockyer (1868)
First isolationWilliam Ramsay, Per Teodor Cleve, Abraham Langlet (1895)


Although there are nine known isotopes of helium (2He) (standard atomic weight: 4.002602(2)), only helium-3 (3He) and helium-4 (4He) are stable. All radioisotopes are short-lived, the longest-lived being 6He  with a half-life of 806.7 milliseconds. The least stable is 5He, with a half-life of 7.6×10−22 s, although it is possible that 2He
has an even shorter half-life.

Main isotopes of helium
Iso­topeAbun­danceHalf-life (t1/2)Decay modePro­duct

Periodic Table of Elements | Complete List of Chemical Elements by Group, Name, Symbol, Color and Type

Periodic table elements
Periodic Table of Elements | Complete List of Chemical Elements by Group, Name, Symbol, Color and Type

Sources: Royal Society of Chemistry, ChemicoolLive ScienceRoyal Society of Chemistry

Photo credit: Wikimedia Commons

Photo explanations: image of a helium filled discharge tube shaped like the element’s atomic symbol.


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