Helium

The second most abundant element in the Universe. The commonest form has two protons and two electrons. There is another isotope, ³He, which has only one neutron.

Helium is the first of the noble gases, and exists on earth as a monatomic gas.

It was first discovered by spectroscopy, when an emission line of a previously unknown element was observed in light from the Sun. Hence the name, derived from "helios", meaning "sun". Because, until its discovery on earth, it was thought that it was probably a

metal, the name ends with "ium" which is the standard name ending for a metal.