Did You Know? #2

What do Helium, Neon, Argon, Radon, Xenon and Krypton have in common?

They are noble gases. Noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity. The abundances of the noble gases in the universe decrease as their atomic numbers increase. Helium is the most common element in the universe after hydrogen. The prices of the noble gases are influenced by their natural abundance, with argon being the cheapest and xenon the most expensive. Noble gases have very low boiling and melting points, which makes them useful as cryogenic refrigerants. Noble gases are commonly used in lighting because of their lack of chemical reactivity. Argon, mixed with nitrogen, is used as a filler gas for incandescent light bulbs. Some noble gases have direct application in medicine. Helium is sometimes used to improve the ease of breathing of asthma sufferers. Xenon is used as an anesthetic because of its high solubility in lipids, which makes it more potent than the usual nitrous oxide, and because it is readily eliminated from the body, resulting in faster recovery. Radon, which is highly radioactive and is only available in minute amounts, is used in radiotherapy.