Helium is element 2 in the periodic table. It is a colorless, extremely inert non-toxic and non-flammable gas.
It is positioned as the second element on the periodic table, holds the distinction of being the lightest among the noble gases. Helium is extremely inert and does not react with anything. Notably, helium has the lowest boiling point of all elements; it remains in a gaseous state even at -267 °C. Under normal atmospheric pressure, it cannot form a solid.
In the universe, helium is the second most abundant element, only behind hydrogen. It constitutes about 23% of the universe’s atomic matter, while the Sun is 9% helium. When the Sun will run out of Hydrogen, it will begin burning Helium into even heavier elements, leading to a Red Giant Phase.
On Earth however, Helium accounts for only 0.0005% of the atmosphere, a stark contrast to other noble gases like argon, which makes up nearly 1%. Helium’s exceptionally low density makes it able to escape Earth’s gravitational pull with ease. However, radioactive active elements like uranium and thorium (which are abundant on Earth), albeit slow, continuously produce helium.
Helium is mostly used as a lifting gas for balloons, but it also has applications in medicine and has unique properties as a superfluid. The most common isotope of Helium is Helium-4 (the nucleus known as an alpha particle in physics), while Helium-3, the other stable isotope is very rare on Earth. The Moon however, unlike Earth, has large deposits of Helium-3. This isotope could be used for nuclear fusion.
In 1868, French astronomer Jules Janssen first identified helium on the sun while observing its spectral lines. This marked helium as an exotic element, a status that was short-lived as it was later found on Earth in 1895 within uranium ore. At the time, the concept of radioactivity was unknown, making the presence of helium in the ore a curious phenomenon. It wasn’t until the discovery of radioactivity and the subsequent understanding of decay chains in 1913 that the occurrence of helium in uranium ore was explained.
Since Helium is very light, and not at all flammable or toxic, it is often inhaled by people to have a low-pitch voice. When excited with light, Helium glows pink.
Helium gas is very inert. Currently, no stable compounds of helium have been found.