Inert Gases
Inert gases, also known as noble gases, are a group of elements characterized by their full valence electron shells, which grant them exceptional stability and a low reactivity level. This group includes helium, neon, argon, krypton, xenon, and radon, all located in group 18 of the periodic table. The stability of these gases means they rarely engage in chemical reactions, although there are minor exceptions, such as xenon and radon's ability to form certain compounds with fluorine.
Inert gases naturally occur in the earth's atmosphere and can also be found in clathrate minerals, where they occupy spaces between other atoms without forming chemical bonds. They are produced industrially through the fractional distillation of liquefied air. Each gas has unique applications: helium is commonly used in balloons and as a carrier gas in labs; neon is well-known for its use in signage; argon serves as an inert atmosphere in welding; and krypton and xenon are primarily utilized in lighting.
Radon poses health risks due to its radioactive nature and its association with cancer, particularly when it accumulates in poorly ventilated spaces. The recently discovered element oganesson is also part of this group, though its properties are less understood, and it may behave differently from the other inert gases. Overall, the unique characteristics of inert gases make them important in both scientific and industrial contexts.
Inert Gases
FIELDS OF STUDY: Inorganic Chemistry; Organic Chemistry; Metallurgy
Abstract
The basic structure and properties of the inert gases are described. The inert gases are a group of elements that have full valence shells and thus are very stable. Such elements include helium, argon, and radon.
The Nature of the Inert Gases
The inert gases consist of the elements helium, neon, argon, krypton, xenon, and radon. They belong to group 18, located at the extreme right-hand side of the periodic table of elements. Their atoms are characterized as having the full complement of electrons in the outermost, or valence, electron shells, which means that such gases rarely lose or gain electrons. This arrangement of electrons is responsible for the extreme stability of the inert gases.
Nearly all of the inert gases are technically breathable, though none has the ability to support respiration. The exception to this is radon, which is a radioactive element formed by the decay processes of naturally occurring radium, thorium, and actinium. It has been identified as a carcinogen that can be formed in minute quantities from minerals normally present in soils and concrete. The accumulation of radon gas in enclosed spaces, such as poorly ventilated basements, has been a cause of concern in some locations.
All of the inert gases are characterized by extreme stability that typically prevents them from undergoing reactions with other materials. This perceived unwillingness to associate with more common elements earned them the popular name of noble gases. That name is preferred by some scientists, as these gases can in rare cases interact with other elements and thus are not truly inert.
The synthetic element oganesson, discovered in 2002 and previously known by the placeholder name ununoctium, also belongs to group 18. Although little is known about its properties, it is expected to share some physical and chemical properties with the inert gases. However, calculations of the element's atomic structure by a team of scientists at Michigan State University and Massey University, featured in Physical Review Letters in February 2018, suggest that under normal conditions, oganesson would take the form of a solid rather than a gas. With the atomic number 118, oganesson is the heaviest known element and fills the very last available square in the current periodic table.
Occurrence of Inert Gases
The inert gases exist naturally in the atmosphere and can also be components of various clathrate minerals. In these, the atoms of the inert gases fill in the spaces between other atoms in a crystalline lattice without being chemically bonded to any. The inert gas atoms are essentially trapped in a cage, and clathrate compounds are thus commonly referred to as "cage compounds." The different gases are produced industrially by the fractional distillation of liquefied air.
Atomic Structure and Reactivity of the Inert Gases
The electron distribution of the inert gases is characterized by the presence of the full complement of valence electrons in the outermost shell of each atom. The completely filled valence shell arrangement prevents the gain or loss of a single electron to form an ion or a covalent bond. Atoms are at a minimum energy state when the electron shells are completely filled, with no odd electrons in the outermost orbitals (specific regions within the electron shells). The stability that this imparts is the reason for the lack of reactivity of the inert gases, although the effect becomes weaker as the size of the inert gas atom increases.
The inert gases typically do not form compounds, with the notable exceptions of the xenon and radon fluorides formed by direct fluorination. The high electronegativity (propensity to attract electrons) of fluorine (F) and the large size of xenon (Xe) and radon (Rn) atoms are sufficient to induce electron pair separation in the atoms of the latter two elements. This enables the formation of a limited number of compounds with fluorine, such as XeF6 and RnF6, in which the xenon and radon atoms take on a formal oxidation state of +6.
Uses of the Inert Gases
Several of the inert gases are well known and commonly used. Helium, the lightest, is less dense than air, which accounts for its use in balloons. It is also used as a carrier gas in analytical laboratory devices and provides an inert, unreactive atmosphere in which air-sensitive reactions can be carried out. Neon is familiar as the colored gas in lighted signs. Argon, which is denser than air, is used as both a carrier gas and an inert atmosphere in such laboratory and industrial applications as aluminum and magnesium welding operations. Krypton and xenon are used primarily in lighting applications. Although radon is best known as a hazard, it has also been used for various scientific applications.
Principal Terms
- fluorination: the addition or substitution of fluorine atoms as substituents in compounds.
- noble gases: a group of gases, including helium, neon, and argon, that occur naturally only as monatomic materials and do not normally form compounds.
- oxidation state: a number that indicates the degree to which an atom or ion in a chemical compound has been oxidized or reduced.
- reactivity: the propensity of a chemical species to undergo a reaction under applied conditions.
- valence electron: an electron that occupies the outermost or valence shell of an atom and participates in chemical processes such as bond formation and ionization.
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"Oganesson—Noble but Not a Gas." MSUToday, Michigan State U, 8 Feb. 2018, msutoday.msu.edu/news/2018/oganesson-noble-but-not-a-gas/. Accessed 23 Apr. 2018.