- Helium (He) is the second lightest and second most abundant chemical element in the universe, positioned in Group 18 of the periodic table as a noble gas with atomic number 2.
- It consists of two protons, typically two neutrons in its nucleus, and two electrons, making it the simplest member of the noble gases.
- Helium is colorless, odorless, tasteless, and chemically inert under standard conditions due to its complete valence electron shell, which makes it highly stable and nonreactive.
- It has two stable isotopes: helium-4 (⁴He), which accounts for over 99.999% of naturally occurring helium, and helium-3 (³He), a rare isotope with unique applications in cryogenics and nuclear fusion research.
- Its extraordinarily low boiling point (−268.93 °C) is just a few degrees above absolute zero, making it the coldest liquefiable substance known.
- Helium’s cosmic abundance is second only to hydrogen, comprising about 24% of the elemental mass of the universe. It is primarily formed in the cores of stars through the nuclear fusion of hydrogen via the proton–proton chain or the CNO cycle, a process that releases vast amounts of energy and marks a key stage in stellar evolution. In the early universe, helium was also created in significant quantities during Big Bang nucleosynthesis, within the first few minutes after the universe’s formation.
- On Earth, helium is rare in the atmosphere because its light atomic mass allows it to escape into space. Most terrestrial helium is extracted from underground natural gas deposits, where it accumulates over millions of years from the radioactive decay of heavy elements like uranium and thorium, which emit alpha particles—⁴He nuclei—during decay.
- The discovery of helium is unique in that it was first identified in the Sun before it was found on Earth.
- In 1868, during a solar eclipse, French astronomer Jules Janssen observed a yellow spectral line in sunlight that did not match any known element.
- Independently, English astronomer Norman Lockyer reached the same conclusion and named the element “helium” after the Greek word helios (Sun).
- Helium’s terrestrial presence was confirmed in 1895 by Sir William Ramsay, who isolated it from the mineral cleveite.
- Since then, helium has found critical roles in science and industry. It is indispensable for cryogenics, particularly in cooling superconducting magnets such as those used in MRI scanners and particle accelerators. It is also used as a shielding gas in arc welding, in leak detection, as a lifting gas for balloons and airships, and in controlled atmospheres for semiconductor manufacturing.
- Helium’s physical properties make it extraordinary among elements. It remains liquid at absolute zero under normal pressure and can only solidify under extremely high pressures.
- Liquid helium exhibits remarkable quantum phenomena, including superfluidity—a state in which it flows without viscosity—when cooled below 2.17 K (the lambda point). This behavior provides scientists with a unique system to study quantum mechanics on a macroscopic scale.
- Helium’s nonflammability and inertness also make it valuable for applications in deep-sea breathing mixtures, where it reduces the risk of nitrogen narcosis and oxygen toxicity for divers.
- Despite its abundance in the cosmos, helium is a finite, non-renewable resource on Earth, and its scarcity has led to growing concerns over supply and conservation, particularly as demand increases for high-tech and medical applications.
