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Group →18
↓ Period
12
He
210
Ne
318
Ar
436
Kr
554
Xe
686
Rn
7118
Uuo
Legend
Noble gas
Gas
Primordial element
From decay
Synthetic

The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with a very low chemical reactivity. They are placed in group 18 (8A) of the periodic table (previously known as group 0). Textflix 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 that element's properties because of 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. Textflix The melting and boiling points for each noble gas are close together, differing by less than 10 °C (18 °F); consequently, they are liquids only over a small temperature range.

Neon, argon, krypton, and xenon are obtained from air using the methods of liquefaction of gases and fractional distillation. Helium is typically separated from natural gas, and radon is usually isolated from the radioactive decay of dissolved radium compounds. Noble gases have several important applications in industries such as lighting, welding, and space exploration. A helium-oxygen breathing gas is often used by deep-sea divers at depths of seawater over 180 feet (55 m) to keep the diver from experiencing oxygen toxemia, the lethal effect of high-pressure oxygen, and nitrogen narcosis, the distracting narcotic effect of the nitrogen in air beyond this partial-pressure threshold. After the risks caused by the flammability of hydrogen became apparent, it was replaced with helium in blimps and balloons.