• Noble gases such as neon are used in fluorescent signs and lighting.neon sign image by pearlguy from Fotolia.com
  
  The six noble gases are all found in group 18 of the periodic table. Noble gases are different from other elements because they have a full set of electrons in their outer shell. Most gases have too few or too many. This complete electron shell makes noble gases very stable, a fact that once saw them referred to as "inert gases." However, some of the noble gases are now known to take part in chemical reactions.
  
  

Helium

• Helium has an atomic number of 2 and is represented by the symbol He. The gas was discovered in 1895, but, according to the BBC website, its existence had been previously proposed by Pierre Jules Cesar and Sir Joseph Norman Lockyer. The two men that named the gas "helium" after the Greek word for sun. Helium is often used in balloons due to its lighter than air properties. It is also used in deep sea diving equipment to dilute a diver's oxygen supply.
  
  

Neon

• Neon has an atomic number of 10 and the symbol Ne. It was discovered in 1898 by two British chemists, William Ramsay and Morris W. Travers, and named after the Greek word for new, "neos." Neon is often used in lighting and fluorescent signs. The gas itself is colorless but glows in an electric discharge.
  
  

Argon

• Argon has an atomic number of 18 and the symbol Ar. It was isolated in 1894 by Lord Rayleigh and William Ramsay, becoming the first of the noble gases to be discovered. The stable nature of the gas earned it the name "argon," the Greek word for inert. According to the Royal Society of Chemistry website, "Argon is widely used to provide an inert atmosphere for high-temperature metallurgical processes." Like neon, it is also used in lighting.
  
  

Krypton

• Krypton is represented by the symbol Kr and has an atomic number of 36. Krypton was discovered in 1898 by William Ramsay and Morris W. Travers, just a few weeks before they discovered neon. It was named after the Greek word "kryptos," meaning hidden. The gas is used in fluorescent lighting and in various types of photographic flash bulbs.
  
  

Xenon

• Xenon has an atomic number of 54 and the symbol Xe. It was discovered by Ramsey and Travers in 1898, shortly after their discovery of neon and krypton, and named after the Greek word for stranger. Xenon is found naturally in the atmosphere, but only in minute quantities. According to the PeriodicTable.org website, xenon is used in photographic flashes, general anesthetic and stroboscopic, bactericidal, and laser-pumping lamps.
  
  

Radon

• Radon, the last noble gas to be isolated, has an atomic number of 86 and the symbol Rn. It was initially observed in the 1890s before being isolated by Friedrich Ernst Dorn in 1900. It was properly classified in 1908 by William Ramsay. Radon is colorless, odorless, tasteless and, unlike the other noble gases, radioactive. It occurs naturally from decaying radium and is considered hazardous due to its radioactivity. It is used in radiotherapy for the treatment of cancer.