On the periodic table, the element with the symbol He is helium.
Helium has atomic number 2 and is a noble gas in group 18 and period 1. It is colorless, odorless, and chemically inert under ordinary conditions because its electron shell is complete. Helium is the second-lightest element after hydrogen.
Helium was first detected in the spectrum of the Sun during the 1868 solar eclipse. Its name comes from Helios, the Greek word for the Sun. It was later found on Earth in uranium-bearing minerals and isolated as a terrestrial element in 1895.
Liquid helium has remarkable low-temperature properties. Helium-4 becomes a superfluid below about 2.17 kelvin, while helium-3 behaves differently because it is a fermionic isotope. Helium is used in cryogenics, leak detection, scientific instruments, and lighter-than-air balloons.
Although helium is common in stars, Earth has limited accessible supplies because the gas is light enough to escape the atmosphere over geological time.