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The noble gases are a group of elements on the periodic table known for their lack of color, odor, and reactivity. Helium and neon are the most common in the universe, but not on Earth. Their full valence shells make them unlikely to react chemically, and they are used in various scientific and industrial processes.
The noble gases, sometimes referred to as inert gases, are elements that make up the 18th group of the periodic table. Elements in groups on the periodic table tend to share many chemical properties. For example, noble gases usually lack any color or odor; they are not flammable; and, in most cases, are unlikely to enter chemical reactions. All of these properties apply specifically under normal temperature and pressure conditions, as different properties can emerge under extreme temperature or pressure conditions. At extremely low temperatures and high pressure, for example, group 18 members become liquid and can be used as powerful cryogenic refrigerants.
The first six noble gases of group 18 are found in nature and some of them are among the most widespread elements known to man. Helium and neon, the first two of the noble gases, are the second and fourth most common elements in the known universe. Each successive noble gas is less prevalent in nature than the previous one. However, the abundance of gases on Earth does not reflect their relative abundance in the rest of the known universe. Helium, for example, is the second most common element in the known universe, but only the third most common noble gas in Earth’s atmosphere.
One of the most notable properties of the noble gases is the low chemical reactivity demonstrated under most conditions. The atomic properties of group 18 elements can be used to explain the low reactivity. The noble gases each have a complete valence shell, which essentially means that all available spaces for electrons are taken. An atom with a full valence electron shell has no particular inclination to react with other atoms or molecules because the reactions involve the sharing or exchange of electrons. Chemical reactions tend to occur because the sharing or exchange of electrons brings the atoms involved closer to a “noble gas configuration” with a full valence shell: a noble gas already has such a configuration, so it is unlikely to react chemically.
Many different scientific and industrial processes make use of various noble gases. For example, liquid helium and liquid neon exist at temperatures close to absolute zero, so they can be used as powerful coolants for superconductors and other devices that operate only at low temperatures. Helium is also commonly mixed with gases used by divers for breathing because it is not as readily absorbed by human tissue as other gases, such as nitrogen, are. The noble gases are also used to provide buoyancy for balloons and airships, to produce lights, and as components of powerful lasers.
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