Noble gases electronic configuration
All the nobel gases do not have same valence electron configuration. Valence electrons are electrons in the outer shell. They all don't have the same configuration because the noble gas helium only has 2 electrons in its outer shell. This is the stable configuration for first shell. The others have 8.
This group has very interesting 18th century history. Cavendish, while passing an electric discharge in a mixture of air and oxygen to prepare oxides of nitrogen and then removing them and oxygen completely, discovered that there always remained a gaseous residue [1/120 of the original volume of air]. He thought might be a new element.
After a lapse of a few years, during a total eclipse of the sun on 18th August 1868, spectroscopic examination of the sun's chromosphere indicated a new atomic spectral line, not observed from any of the known elements. This suggested the presence of a new element in the sun and the name Helium from Greek word ‘helios’ (meaning sun) was given to it.
Ramsay in 1895 while making a spectroscopic examination of a gas obtained from the mineral clevite, observed helium lines. Thus its presence on the earth was also established. During the same year another member named “Argon” (the lazy one) was discovered and named so because of its inert character. In the next four years other gases namely Krypton, Xenon and Neon were also isolated.
This family was also called rare gases because they occur in relatively small amounts in the atmosphere. Helium is also found as the occluded gas in some of the radioactive minerals and can be released on heating. Others are obtained by fractional distillation of liquid air.