Symbol He
Atomic Number 2
Atomic Mass 4.003
Discovered by Helium was discovered by Sir William Ramsay in London, and independently by Per Teodor Cleve and Nils Abraham Langlet in Uppsala, Sweden.

What is Helium?

  • Helium is the element which you can find on the upper right side of the periodic table with atomic number 2. It comes first amongst the family of the noble gases.
  • It holds one atomic orbital and was named by Lockyer and Frankland. Its name is derived from the Greek word “Helios” meaning Sun. Scientists knew there is an enormous amount of helium in the Sun before it was discovered.
  • Helium falls under inert gas since its outermost electron orbital is full with two electrons. Helium can also be found in lasers, compressed air tanks and coolant in nuclear reactors.
  • It holds the lowest boiling and melting points among the all other elements. The Nuclear fusion of hydrogen in stars generates a significant amount of helium.


Helium has two known stable isotopes – 3He and 4He. The abundance of helium-3 and helium-4 corresponds to 0.0002% and 99.9998% respectively. This difference in abundances can be observed in the Earth’s atmosphere, where the ratio of 4He atoms to 3He atoms is approximately 1000000:1.

Physical Properties of Helium

Helium (He) Physical Properties
Melting Point 0.95 K (or -272.2oC)
Boiling Point 4.222 K (or -268.928oC)
Density 0.1786 g/L at STP; 0.145 g.cm-3 at its melting point
Critical Temperature and Pressure 5.195 K; 0.227 MPa
Triple Point 2.177 K; 5.043 kPa
Appearance (at STP) Colourless gas

Chemical Properties of Helium

Helium (He) Chemical Properties
Electron Configuration 1s2
First Ionization Energy 2372.3 kilojoules per mole
Second Ionization Energy 5250.5 kilojoules per mole
Van der Waals Radius 140 picometers
Enthalpy of Fusion 0.0138 kilojoules/mole

Uses of Helium

  • The primary use of Helium goes in altitudes research and meteorological balloons.
  • It is utilized as an inert protective gas in autogenous welding.
  • It is the only cooler capable of declining temperature lower than 15K (-434ºF).
  • Helium is also used in the production of germanium crystals and silicon crystals.
  • Since it has the ability to diffuse through solids much faster than air, helium is used industrially for pipeline leak detection.
  • This element is also used in gas chromatography as a carrier gas.
  • Owing to its low melting point, liquid helium has numerous applications in cryogenics, magnetic resonance imaging (MRI), and superconducting magnets.

Practise This Question

Choose the type of prism which was used in Biot's experiment.

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