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What is Helium

Helium (pronunciation: HEE-lee-em) is a colorless, odorless element classified as a non-metal, belonging to the group of inert gases in the periodic table and is represented by the chemical symbol He [1, 2, 3]. It is a monoatomic gas that forms weak diatomic molecules only at temperatures close to -273.15 °C or “the absolute zero” [4].


Helium has nine known isotopes out of which 3He and 4He are stable with natural abundances of about 0.0002% and 99.9998% respectively [5]. Its radioactive isotopes are short-lived, with 6He being the longest-lived characterized by a half-life period of 806.7 milliseconds while 5He is the least stable with a half-life period of 7.6 X 10-22 seconds [5].


Where is Helium Found

Helium is the second-most abundant element found in the universe only after hydrogen [1]. It is found in all stars and is formed on the Earth from radioactive elements when they undergo alpha-decay [1]. For natural dynamic balance, the low-density helium escapes into the Earth’s atmosphere and then to outer space [1]. The price of extracting the element from the air is very high, and so, it is commercially obtained from natural gas that can contain about 7% helium by volume [1].

The top 3 helium producers are USA, Algeria, and Russia while top helium reserve holding countries include USA, Qatar, and Algeria [1].


Origin of its Name: It is derived from ‘Helios’, Greek for the Sun, as it was first identified as the gas that constitutes the Sun’s corona [1]

Who discovered it: The element was discovered by the Scottish chemist Sir William Ramsay and independently by the Swedish chemists Nils Abraham Langlet and Per Teodor Cleve [1, 2].

Liquid Helium

When and How was it Discovered

Before the discovery of helium on Earth, it was found on the Sun [2]. In 1868, the French astronomer Pierre Janssen studied a total solar eclipse in India and found a yellow line while measuring the Sun’s spectrum [1, 2]. An English astronomer, Sir Joseph Norman Lockyer, also observed the same spectral line and presumed that it was caused by an unknown metallic element, which he named helium [1, 2].

In 1895, William Ramsay experimented with cleveite, a radioactive mineral containing uranium and collected the gas that formed after its dissolution in sulfuric acid [1, 2]. He sent the sample to Sir William Crookes and Norman Lockyer, who identified the helium within it [2]. In 1895, at Uppsala, Sweden, Abraham Langlet and Teodor Cleve independently collected the gas produced after dissolving uraninite (UO2) in acid [1, 2]. They found its atomic weight and declared that it was helium [1].

Helium Lewis Dot Structure.jpg

Helium Identification

Atomic number 2 [1]
CAS number 7440-59-7 [1]
Position in the periodic table Group Period Block
  18 [1] 1 [1] s [1]

Properties and Characteristics of Helium

General Properties

Relative atomic mass 4.003 [1]
Atomic mass 4.003 amu [1]
Molar mass 4.0026020 ± 0.0000020 g/mol [6]
Molecular weight 4.003 g/mol [7]
Mass number 4 [8]

Physical Properties

Color Colorless [1, 4]
Melting point/freezing point  Unknown [1]
Boiling point -268.928 °C, -452.07 °F [1]
Density 0.000164 g cm-3 [1]
State of matter at room temperature (solid/liquid/gas) Gas [1, 4]
Thermal (heat) conductivity 0.1513 W/(m K) [9]
Specific heat 5193 J kg-1 K-1 [1]
Bulk modulus Unknown [1]
Shear modulus Unknown [1]
Young’s modulus Unknown [1]
Vapor pressure
– Temperature (K) 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
– Pressure (Pa)

Chemical Properties

Oxidation states/oxidation number/valence 0 [10]
Isotopes Isotope Mass Abundance (%) Half-life Mode of decay
  3He 3.016 0.000134
  4He 4.003 99.9999

Helium Orbital Diagram

Atomic Data of Helium (Element 2)

Valence electrons 2 [11]
Quantum numbers
– n 1 [11]
– ℓ 0 [11]
– m 0 [11]
– ms -1/2 [11]
Electron configuration (noble gas configuration) 1s2 [1]
Atomic structure
– Number of electrons 2 [4, 8]
– Number of neutrons 2 [4, 8]
– Number of protons 2 [4, 8]
Radius of Atom
– Atomic radius 1.400 Å [1]
– Covalent radius 0.37 Å [1]
Electronegativity (Pauling-scale) Unknown [1]
Electron affinity Not stable [1]
Ionization energy (kJ mol-1) 1st 2nd 3rd 4th 5th 6th 7th 8th
  2372.322 5250.516

Helium Electron Configuration (Bohr Model)

What is Helium Used for

  • As a coolant, helium is used in MRI scanners’ superconducting magnets, NMR spectrometers, and the Large Hadron Collider [1]. It is used to cool instruments in satellites and space vehicles [1].
  • The gas is used to fill weather balloons, airships, and decorative blimps due to its low density [1, 4]. Despite hydrogen being more buoyant and cheaper, helium is preferred because it is non-flammable [15].
  • It can be used for pressurizing and cooling the liquid fuel (liquid hydrogen) in rockets and space vehicles [1, 4].
  • Since helium is extremely unreactive by nature, it can provide a protective atmosphere for arc welding, as well as manufacturing semiconductors and fiber optics [1, 4].
  • For people working under pressurized conditions, like deep-sea divers, 80% helium is mixed with 20% oxygen to create an artificial atmosphere [1, 4]. Divers use helium because it leaves their body faster as compared to nitrogen, helping in faster decompression [4].
  • It is used for detecting leaks in air-conditioning systems of automobiles and for inflating car airbags after the accident [1].
  • Helium-neon laser barcode scanners are used in supermarket checkouts [1].
  • Electron microscopes are now replaced by helium-ion microscopes for their better image resolution [1].

Symbol for Helium

Helium Toxicity and Health Effects

Helium is not known to be toxic and does not play any biological role [1]. Although it is commonly believed that inhaling it causes the voice to temporarily become high-pitched [4, 12], heavily inhaling helium can cause an obstruction, cutting off oxygen supply [13].

Interesting Facts

  • The graphical representation of helium shows the Sun, indicating the origin of its name from the Greek word ‘Helios’ and its presence in the Sun [1].
  • The Federal Helium Reserve near Amarillo, Texas has about 40% of the helium gas used by the Americans in a year [3].
  • Since helium turns into a superfluid state at about -271 °C, it is used by the scientists for studying the behavior of superfluids [3].

Cost of Helium

While the price of pure helium is about $0.052 per gram, liquid helium costs roughly $5 per liter [4, 14].



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