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The noble gases are a group of chemical elements that share a high degree of similarity in their properties: under standard conditions, they are all odorless, colorless, monatomic gases, with a very low chemical reactivity. They are placed in group 18 of the periodic table. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). So far, three atoms of the next member of the group, ununoctium (Uuo) have been synthesized in a supercollider, but very little is known of its properties due to the tiny amount produced and its short half-life. The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be "full", giving them little tendency to participate in chemical reactions, and only a few hundred noble gas compounds have been prepared as of 2008. Noble gases have several important applications in industries such as lighting, welding, and space exploration. Helium is often used in scuba diving to replace part of the breathing mixture. After the risks caused by the flammability of hydrogen became apparent, it was replaced with helium in blimps and balloons. (more...)
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